coastal flooding case study

East Coast flooding in UK – 5th December 2013

On Thursday 5th December 2013 large areas of the east coast of England were affected by coastal flooding on a scale not seen since the  Great floods of 1953 . A combination of factors led to the storm surge that was responsible for flooding. This included a high spring tide, an area of low pressure and high northerly winds.

Tidal surge graph spurn 2013 – source: http://www.tides4fishing.com/uk/england/spurn-head

The  tidal coefficient  was 94(very high). The  tide heights  were 0.9 m, 7.1 m, 1.1 m and 7.2 m. We can compare these levels with the maximum high tide recorded in the tide tables for Spurn Head which is of 7.6 m and a minimum height of 0.3 m.

What is a storm surge and why does it happen?

Video from the BBC –  http://www.bbc.co.uk/news/uk-25229885  Met Office Article –  http://www.metoffice.gov.uk/learning/learn-about-the-weather/weather-phenomena/storm-surge  The Atlantic storm, which brought the coastal flooding and gale-force winds of up to 100mph, caused widespread disruption across the UK and claimed the lives of two men – in West Lothian, Scotland, and in Retford, Nottinghamshire.

The Environment Agency said 800,000 homes in England had been protected by flood defences and better forecasting had given people “vital time” to prepare. The agency said sea levels had peaked at 5.8m (19ft) in Hull – the highest seen by the East Yorkshire city since 1953 – and 4.7m (15ft) in Dover, Kent, the highest recorded there in more than 100 years.

Preparing for the 2013 storm surge:

Video report:  http://www.bbc.co.uk/news/uk-25237082 Thousands evacuated:  http://www.bbc.co.uk/news/uk-england-norfolk-25228834

Warnings issued:  http://www.metoffice.gov.uk/news/releases/archive/2013/storm-surge Preparing your home:  http://www.bbc.co.uk/news/science-environment-20497598 Thames Barrier raised:  http://now-here-this.timeout.com/2013/12/05/thames-barrier-to-close-tonight-as-forcasts-predict-the-biggest-storm-surge-for-30-years/ How the barrier works:   http://www.environment-agency.gov.uk/homeandleisure/floods/38359.aspx  The Environment Agency estimates that 800,000 homes and businesses were saved due to flood defence schemes.

Impacts of December 2013 floods:   Social Impacts

Thousands of people were evacuated from Britain’s east coast of England. Victims of the most serious tidal surge in 60 years have been warned to avoid direct contact with floodwater and beware of rats moving into homes.More detail and pictures here:  http://www.dailymail.co.uk/news/article-2519891/Beware-invasion-flood-rats-Homeowners-hit-tidal-surge-told-avoid-contact-water-amid-fears-pest-invasion.html

People Urged to remain vigilant:  http://www.independent.co.uk/news/uk/uk-weather-warnings-scotland-and-north-battered-by-100mph-winds-as-biggest-tidal-surge-in-60-years-threatens-east-coast-8984542.html

Impacts of the December 2013 floods:  Economic Impacts

Economic impact in North Norfolk –  http://www.northnorfolk.org/files/Tidal-surge-combined-info.pdf Seven Cliff Top Homes Collapse in Hemsby –  http://www.bbc.co.uk/news/uk-england-norfolk-25254808

1,400 homes were flooded, including 300 in Boston, Lincolnshire, according to Environment Agency (EA) figures.

Some good images and videos on the Daily Mail website:  http://www.dailymail.co.uk/news/article-2518340/Britain-battered-worst-tidal-surge-60-years-Sea-walls-breached-20ft-waves-smash-string-east-coast-towns.html

VIDEO – Bungalow falls off cliff in Norfolk  http://www.bbc.co.uk/news/uk-25258149 VIDEO – Thousands evacuated:  http://www.bbc.co.uk/news/uk-25253733 VIDEO – Homes in Whitby flooded:  http://www.bbc.co.uk/news/uk-25257747  plus: http://www.bbc.co.uk/news/uk-25258150 VIDEO – Cleaning up after the floods:  http://www.bbc.co.uk/news/uk-25257754 VIDEO – Aerial footages of flood aftermath:  http://www.bbc.co.uk/news/uk-25260863

Today’s most popular pages

Coasts menu

Sea level rise, hard engineering, privacy overview.

Pin It on Pinterest

You must be logged in to post a comment.

• Open access
• Published: 29 October 2018

Coastal flood risk: improving operational response, a case study on the municipality of Leucate, Languedoc, France

• Paul Durand 1 , 2 ,
• Brice Anselme   ORCID: orcid.org/0000-0001-9048-7251 1 , 3 ,
• Stéphanie Defossez 4 , 5 ,
• Sylvain Elineau 2 , 6 ,
• Monique Gherardi 4 , 5 ,
• Lydie Goeldner-Gianella 1 , 2 ,
• Esméralda Longépée 7 , 8 &
• Alexandre Nicolae-Lerma 6  

Geoenvironmental Disasters volume  5 , Article number:  19 ( 2018 ) Cite this article

4228 Accesses

7 Citations

Metrics details

Climate change and rising sea level will certainly lead to significant changes in the management of low-lying coastal areas in the coming decades. While the most recent studies in the field of coastal storms-related flooding are increasingly integrated, simultaneously addressing hazards and vulnerability, as well as population risk perception, there is still little work to consider the preparedness of stakeholders to manage crises whose frequency and intensity are likely to increase in the next years.

The aim of this paper is to expose the major results of the CRISSIS research program, which proposed a multi-disciplinary approach to the management of coastal flood risk in a town particularly exposed on the French Mediterranean coast. The originality of the project was to offer both an integrated approach to risk by analysing its 3 dimensions (hazard, impact and vulnerability, and representations and perceptions held by populations and stakeholders, or « risk culture ») and a very operational section focused on the evaluation of crisis management measures led by local stakeholders. To achieve this objective, two crisis exercises were organized, the first one to test the assimilation by the municipality staff of existing crisis management procedures and the second to allow local actors to integrate in their crisis management procedures the new risk knowledge data issued from research conducted under the program.

The project has had three main features; (i) it accurately mapped the submersible areas that present a critical vulnerability, both material and human; (ii) it revelated the poor social representation of marine submersion risk, as well as the obvious lack of awareness of crisis management systems and tools and the behavior to adopt in the event of flooding; (iii) Finally, it highlighted the need, through the crisis exercises, for a better assimilation by the municipality staff of the crisis management procedures defined in the Municipal Rescue Plan.

The CRISSIS project has demonstrated the usefulness of an integrated and operational approach of coastal flood risk, not only in terms of studying hazards, stakes and vulnerability, but also in terms of crisis management, in particular through the organisation of crisis simulation exercises.

With global warming causing a rise of sea levels, the vulnerability of coastal towns to flooding risk during storms has increased. This issue is bound to become a key element in the management of low coastlines in decades to come, and multiple studies have been published on this subject in recent years (Cariolet et al. 2012 . Vinet et al., 2012; Hurlimann and al. , 2014; Duan et al. 2014 and Duan et al. 2015 ; King and al. , 2014; Rulleau et al., 2015). While earlier studies were often relatively segmented, focusing either on the hazard itself or on impact and vulnerability, more recent research programs on the topic have been much more integrated, simultaneously addressing hazards and vulnerability, as well as the population’s perception of risk – see for instance the French programs MISEEVA (2008–2011), JOHANNA (2010–2013), BARCASUB (2010–2013), COCORISCO (2011–2014), and European studies on the management of marine flooding and submersion risk (Samuels et al. 2008 ; Sorensen et al. 2017 ).

The two-year CRISSIS program (Characterizing Submersion Risks in Sensitive Sites), launched in 2015 in a coastal town of the French region of Languedoc (municipality of Leucate), falls under this last category: through a multi-disciplinary approach associating geographers, modelers, GIS specialists and crisis and risk management experts, the project offers an integrated perspective on coastal flooding by exploring this risk’s three dimensions in coastal areas (hazard; impact and vulnerability; and representations and perceptions held by populations and stakeholders, or « risk culture »). This study does however stand out from other literature, in that it also includes a very operational section focusing on the evaluation of crisis management measures led by local stakeholders – an aspect that has rarely considered by research programs so far.

The preparedness of stakeholders to manage crises whose frequency and intensity is likely to increase is a key element in the management of vulnerable coastal spaces. Several studies have shown that the damages caused by recent disasters in coastal areas have been aggravated by the local authorities’ lack of preparedness (Daniels et al. 2011 ; Genovese et al. 2011 ; Genovese and Przyluski 2013 ). It is not enough to know and prevent risk: we also need to be prepared to manage the resulting crises (Lagadec 1993 , 2001 , 2004 , 2012 ; Egli 2013 ). In this perspective, the CRISSIS project aims to help local stakeholders use the new findings produced through the analysis of the three dimensions of risk. Two crisis management exercises were thus organized from the outset: one took place halfway through the project to test the uptake of crisis management procedures (« Plan Communal de Sauvegarde » (PCS), or « Municipal Rescue Plan ») by local authority staff; a second more ambitious test took place at the end of the program, with the objective of testing the PCS again but this time by integrating new data produced as part of the program’s findings. Overall, the objective of CRISSIS has been to both generate new knowledge to improve risk prevention and help optimize crisis management by local stakeholders by facilitating the prioritization and classification of actions in the event of a flood. After a brief introduction of its study area, this paper will describe the methodology that guided its operational approach to coastal flood risk, before presenting its key findings.

The area chosen for this study is the municipality of Leucate, a town located on the French coastline of the Languedoc region. The municipality comprises of four seaside resorts located on both sides of the Leucate cape. These include from South to North: the resort of Port Leucate, built in the seventies as part of the Racine development scheme, on the coastal strip that cuts across the Salses-Leucate lake; the nudist village located on the narrowest part of the strip; Leucate Plage, at the foot of the cape’s southernmost cliff; and La Franqui, at the foot of the cape’s northern cliff. The area is affected by large-scale urban and touristic issues, as the town is densely populated during the summer season, growing from 5000 year-round residents to almost 100,000 during the high season. The urban areas of Port Leucate and Leucate Plage are also very exposed to coastal flood hazards, and in particular Port Leucate which was built on a strip of low altitude coastal land (for the most part under 3 m NGF). Both areas are periodically flooded when strong south-eastern storms occur (Ullmann 2009 ), during which the waves can cause the sea level to rise to up to 3 m NGF (Anselme et al. 2011 ). The floods can also be aggravated by a combination of wind and heavy rainfall, causing the lake’s level to rise and provoking major runoff down the cliffs of the cape (Fig. 1 ).

Location of study area

Paradoxically, in spite of its high vulnerability to risk (the state of natural disaster has been declared 14 times in the area since 1982, including 13 times for “flood/submersion” events, GASPAR database of the French Ministry of Ecological Transition, http://www.georisques.gouv.fr/acces-aux-donnees-gaspar ), the town of Leucate has been relatively slow in applying risk regulation measures in comparison with other municipalities located on the Languedoc-Roussillon coastline. According to a recent publication of the Department of Planning and Housing of the Rhône-Mediterranean basin (DREAL Rhône-Méditerranée 2016 ), the first PPRI (“ Plan de Prévention des Risques Inondation ”, or “Flood Risk Prevention Plan”) was only adopted in November 2012, while all the other municipality in the region subject to marine submersion risk had already had one for several years, and to this day this document has not made it past assessment stage. A local Municipal Safeguarding Plan (PCS) was adopted in December 2014 after the town was hit by two violent storms in March 2013 and November 2014.

In this context combining strong hazard and major vulnerability, the local authorities only appear to have become aware of risk very recently. The town of Leucate therefore provides an interesting site to experiment with the integrated and operational marine submersion risk management approach developed by the CRISSIS program.

Methodology: An integrated and operational approach to marine submersion risk

The CRISSIS approach integrates the three dimensions of submersion risk:

The hazard and its predictable evolution in the context of climate change: digital simulations of sea level variations caused by storms or other factors, and of runoff propagation into urban areas, and high-resolution mapping of findings;

Vulnerability: structural vulnerability of buildings and human vulnerability of inhabitants (based on age and mobility criteria), mapping of potential damages to constructions and associated human issues;

Perceptions and representations held by the population (or “risk culture”), captured through a geo-sociological survey aimed at quantifying risk culture levels; production of a map of findings to help improve information management and awareness-raising activities.

This project aims to improve both risk prevention and crisis management by local authorities. This aspect forms the fourth phase of the program: it consisted in developing exercises to test crisis management mechanisms and procedures based on existing operational documents (PCS), complemented by new data produced through our analysis of the three dimensions of risk.

Analyzing hazard using a numerical modeling system

In France, coastal flood hazards are still often approached through basic mapping methods obtained by cross-referencing the topography of exposed areas with extreme water levels, estimated through a statistical analysis of marine weather forcing conditions. This methodology was for instance used to elaborate official risk exposure documents (Coastal Flood Risk Prevention Plan or PPRSM) for the Mediterranean coastline. These basic methods are not however suited to optimal crisis management. They only produce schematic maps that do not include the event’s kinetics, the detail of the process that caused the flood (inundation, overtopping of a barrier, breaching of flood defense structures…), or the specificities of water propagation in urban area. Furthermore, this type of mapping associates the hazard with extreme statistical characteristics, which is not always compatible with the need for precise information in cases where the crisis might have been caused by a lower-intensity event.

Digital modeling is now increasingly used to map out hazards, using chains of models to recreate the process that caused the flood: inundation, overtopping, breaching of flood defenses, etc. (Gallien et al. 2014 ; Guimarães et al. 2015 ; Le Roy et al. 2015 ; Nicolae et al. 2018 ). Recent improvements, both in terms of technical developments and of pre- and post-data processing, have made it possible to integrate both the phenomena that contribute to floods (rise of average sea level, waves, river water) and their chronology (duration of floods, breaching of defense structures, synchronicity of the maximum values of sea and river levels). This has made it possible not only to identify risk areas, but also to evaluate timescales and potential response times between the start of an event and the point where communication lines or strategic buildings are damaged. Some important efforts are currently being deployed using meta-modeling or machine learning to achieve a real-time forecast of floods (Goulby et al., 2014; Jia et al., 2015; Rohmer et al., 2016). However, this work remains too experimental to be used in an operational setting. The most effective solution for mapping out such hazards remains combining a statistical analysis of the varying intensity of marine weather conditions with a field diagnosis of local vulnerabilities (coastal narrow dune, fragile seafront structures, water drainage system…): we can thus elaborate multiple scenarios in consultation with local stakeholders, and produce a tool to support decision-making in crisis situations.

The CRISSIS project therefore chose to work from a numerical modeling system to characterize flood hazard. The modeling is based on a chain of models – MARS (Lazure and Dumas 2008 ), SWAN (Booij et al. 1999 ), SWASH (Zijlema et al. 2011 ) – in order to model the variation in sea levels caused by storm conditions (atmospheric pressure, wind set-up) and the contribution of wave set-up to the rise of average sea levels, and to assess the volume of water overtopping the seafront and the propagation of the water on land (Nicolae et al. 2015 ; Nicolae et al. 2018 ). The modeling process comprised of two stages.

Stage 1: Testing and validating the modeling system

The test consisted in simulate two recent storms (March 2013 and November 2014) that presented diverse weather conditions and consequences in terms of flood on the area of study. The all description of the validation process is detailed in Nicolae et al. 2018 and only main results are presented here. Data, which was used to recreate similar weather conditions on the site of Leucate, is listed in Table  1 .

Information has been collected from multiple sources (press, photos, interviews, testimonies, report from technical services, etc.) to characterize flood events (intensity, sea level, chronology). We were thus able to retrace the affected areas and the chronology of events. These observations, although mostly of a qualitative nature, enabled us to estimate the level reached locally by the flood based on human landmarks (sidewalks, walls, quays). These points of observation were cross-referenced with LIDAR data and/or DGPS measurements collected through a field campaign, in order to quantify in term of water height each qualitative observation. The reach of the flood waters extension limit in the most heavily affected areas was also mapped out, consulting local authority staff who had worked on the ground during the storms. In the absence of local records of water levels in the port, the information collected and converted in water height (in reference to the French terrestrial datum, IGN69) provided a valuable information to assess the quality and precision of the modeling of water levels and submersion in various sites across the municipality. The water levels generated through the simulations were compared with those deduced from the analysis of topographic landmarks (quays, roads) that appeared on photographs to be submersed or not by the floods. By looking at various landmarks across the port area, we established that the average water level in the port was 0.85 m IGN +/− 5 cm IGN in 2013, and 1.05 m IGN +/− 5 cm in 2014. The water levels generated by simulations in the area were within a similar range to those estimated from photographic observations (a discrepancy of under 5 cm was observed for the 2013 simulation, and an underestimation of about 10 cm for 2014), which indicated that the performance of the modeling system was relatively reliable.

Stage 2: Elaboration of submersion scenarios

After validating the modeling system, we developed various submersion scenarios, based on a multivariate statistical analysis of extreme values (joint probability of waves/water levels). This analysis enabled us to define low-probability marine conditions (with a return period of 100 years), which were propagated to the shore and then to the land (Nicolae et al. 2018 ). These simulations enabled us to characterize the reach and intensity of floods for hundred-year events, and to anticipate the consequences of a gradual rise of the average sea level under the effect of global warming. This data was fed into a GIS in order to create relevant maps for crisis management exercises.

Assessing the vulnerability of buildings and populations

Over the past few years, the geographic understanding of natural hazards shifted from a hazard-centered approach to a vulnerability-centered approach, integrating the social dimension of hazard. Such a diagnosis and evaluation of vulnerability presents advantages in terms of anticipating risk and mitigating its impacts. Although this notion has evolved, vulnerability can be understood both in its primary meaning as the capacity to withstand damage (D’Ercole et al. 1994 ) but also as the capacity to cope with damage (Thouret and D’Ercole 1996 ), thus echoing the concept of resilience. Resilience is perceived as the positive counterpart to vulnerability, which usually carries negative connotations due to its association with fragility, although the two terms are not mutually exclusive (Reghezza Zitt and Rufat 2015 ).

This study considers the geographic dimension of risk on an infra-municipal scale, with a vulnerability diagnosis focusing on individual issues (on the scale of a building). The notion of vulnerability implies an assessment-centered approach (Leone et al. 1996 ; Becerra 2012 ), which must begin with the identification of criteria and indicators. Many recent studies on the subject show the relevance of this methodology (Barroca et al. 2005 ; Leone 2007 ).

As part of this research project in Leucate, the diagnosis of material and human vulnerability was evaluated on multiple scales. We first assessed the vulnerability of material goods exposed to hazards, considering that vulnerability also affects the rest of the area (D’Ercole and Metzger 2009 ). In addition, we carried out a comprehensive diagnosis of material and human vulnerability, considering the dangerousness of each building located in a high-risk area in the municipality. Within this sample, we carried out a diagnosis of first homes, second homes and tourist accommodation (about 4000 buildings) as well as commercial premises (about 100). However, to further elaborate our vulnerability criteria – and more specifically those relevant to human vulnerability – a diagnosis was drawn based on a perception survey (see below). Additional evaluation criteria were used for this sample, but they only covered 400 buildings (tourists who do not own their accommodation were excluded from the sample).

The criteria were set to capture the potential damages caused by coastal floods, assessing both material vulnerability (type and condition of building) and human vulnerability with indicators assessing people’s access to safety. The advantage of using two different samples was that they provided an operational diagnosis across the area affected by risk. This also helped us respond to the expectations of local authorities, by showing that a more in-depth diagnosis could be carried out to improve crisis management by identifying and locating vulnerable individuals.

The surveys included questions based on vulnerability criteria and indicators (extract: see Table  2 ). The methodology used to assess vulnerability was adapted to the local context of the municipality of Leucate, using evaluation criteria that had been designed for other locations and hazards and had been proven to be relevant to this site (Leone 2007 ; Meur-Ferec et al. 2011 ; Lagahé and Vinet 2014 ).

Some criteria capture both material and human vulnerability, while others only capture one type of vulnerability.

A vulnerability index was developed from these criteria. When taken individually, a criterion only captures a partial assessment of one specific type of vulnerability. However these criteria and indicators can be combined to provide a global assessment of vulnerability, where some criteria are compensated by others.

The methodology followed to create this index consisted in setting a hierarchy between indicators and criteria, by using an intra- and inter-criteria weighing system. The hierarchy was based on the bibliography and on past studies on this topic, as well as on a global reflection on the importance of a given criteria in comparison with another, always from the perspective of a scenario of potential damage. We were thus able to elaborate maps that were fed into the development of crisis exercise scenarios.

Perception analysis and representations of risk

An understanding of the perceptions, behaviors and reactions of individuals and groups of individuals in the face of any kind of risk should form a prerequisite to the development of prevention and management policies (Ruin 2010 ). This process can help researchers better grasp the discrepancy between the knowledge of experts and that of laypersons (Baggio and Rouquette 2006 ). The perception of risk varies between individuals: studies on this topic attempt to characterize groups of individuals that share a relatively similar perception of a given risk (Hellequin et al. 2013 ). An individual’s perception of risk is influenced by four factors: their experience of risk (through direct or indirect experience), their knowledge on this risk (lay or academic), their social and economic interests (attachment to a place, value of property, socio-economic standing of household, etc.), and their values (moral, political, etc.). Over the past twenty years, the analysis of perceptions and social representations has played an increasingly prominent part in research programs on French coastal towns’ vulnerability to marine hazards (Goeldner-Gianella and Chionne 2014 ; 2002–2004: PNEC, Nord-Pas-de-Calais; 2007–2011: ANR MISEEVA, Languedoc - Roussillon; 2011–2014: ANR COCORISCO, Bretagne, etc.). These studies have highlighted the weakness of social representations of coastal risks (erosion and marine submersion) and even the “blatant absence of a risk culture” (Chauveau et al. 2011 ). Most surveys show that the populations affected feel little concern for coastal risks. They do not reflect on their situation, and nor do they actively seek out information or design any action plans in the event of a disaster (Hellequin et al. 2013 ; Flanquart 2014 ; Krien 2014 ). When questioned, the people surveyed tend to make up a spontaneous discourse on the question by drawing from their memories, sensations and incomplete reflections on the question. Krien ( 2014 ) explains that people’s representation of coastal risks is the product of a social construct developed from their overall representation of risk, the sea, storms and the place where they live.

In order to measure risk culture levels in the municipality of Leucate, the methodology focused on three main angles: questionnaire-based surveys of inhabitants; semi-structured interviews with key stakeholders; and a discourse analysis of the local news bulletin, Cap Leucate . In total, we screened 46 issues ranging from January 2010 to June 2015 (the bulletin is monthly in theory), which underwent an assisted textual analysis using the Tropes software (Pont 2015 ). The term “ submersion ” ( “ submersion”) appears in the newsletter for the first time in the March 2015 issue, to refer to the municipal rescue plan established by the local authorities, and in an article that announces the launch of the CRISSIS research project. Before the creation of official documents (PCS and PPRL), municipal authorities would use the word “ inondation ” (“inundation”) when referring to coastal floods. The word “ inondation ” was written sixteen times, including three times during the 2013 flood that hit Leucate Plage, and three times in 2015 in relation to the announcement of this research program.

The questionnaire survey was communicated to 493 people including first home owners, holiday home owners and tourists living in Port Leucate, the naturist village and Leucate Plage (Table  3 ). The survey was carried out from april to june 2015. At this time of year, many holiday homes are unoccupied, making it easier for us to survey residents and secondary home owners. The surveys were conducted face-to-face at the respondents’ homes and lasted 20 to 40 min. The people present were rather suspicious, we had several refusals. Overall, the questionnaires were well completed, with respondents answering 93% of the questions. It would have been useful to base our population and location sampling on the modeling of submersible areas and of the vulnerability of buildings, which were described above. However, as the duration of the program was limited to two years, we had to carry out all research activities simultaneously, and were not able to use this sampling methodology. Individuals were surveyed on: (1) the appeal of the Leucate municipality and its leisure activities; (2) their perception of the area’s and of their accommodation’s exposure to coastal flood risk; (3) their awareness of this risk in Leucate; (4) their presumed reaction in the event of a submersion; and (5) their expectations in terms of communication about this risk. The final objective was to map out representations of risk, in order to help shape the local authorities’ information and awareness-raising activities on coastal flood risk.

Testing crisis management procedures through crisis exercises

Crisis exercises: a brief state of the art.

The last stage in the CRISSIS program’s integrated approach brought added operational value to the project. Recent research on risk assessment in coastal areas – for instance in the Languedoc Roussillon region, the projects RNACC (“ Risques Naturels, Assurances et Changement Climatique ” [“Natural Risk, Insurance and Climate Change”], Yates-Michelin et al. 2011 ) and ANR MISEEVA (2008–2011, Vinchon et al. 2011 ; Meur-Férec et al., 2011) – did not go as far as integrating crisis management. And yet the preparedness of local authorities is essential. Any failings on their part can significantly amplify the impact of extreme phenomena in coastal areas, turning a crisis into a full-blown disaster (Daniels et al. 2011 ; Genovese et al. 2011 ). This is particularly true in regions where the stakes are high and diverse, and where a crisis can involve multiple public and private stakeholders. Local players should therefore be trained in crisis management, including by organizing crisis exercises (Lagadec 1993 , 2001 , 2012 ; Stern 2014 ).

To meet this challenge, public authorities in many countries have developed emergency management systems for using by stakeholders and organize regularly large-scale crisis exercises to prepare institutions and populations to cope with major crises. Thus, in the USA, following huge forest fires in California and Arizona in the 1970s, which had highlighted a lack of coordination of emergency response between different actors, several states have developed the Incident Command System (ICS), which, after the attacks of September 11, 2001, was extended to all US states and integrated into the National Incident Management System (NIMS). NIMS is “a consistent nationwide approach for Federal State, and local governments to work effectively and efficiently together to prepare for, respond to, and recover from domestic incidents.. To provide for interoperability and compatibility among Federal, State, and local capabilities, the NIMS will include a core set of concepts, principles, terminology, and technologies covering multi-agency coordination systems; unified command; training; identification and management of resources ; qualifications and certification; and the collection, tracking, and reporting of incident information and incident resources” (Anneli 2006 ). To regularly train the stakeholders, the FEMA (Federal Emergency Management Agency) has a National Exercise Program, https://www.fema.gov/ned ) which regularly runs large-scale drills simulating the occurrence of cyclones, earthquakes and tsunamis. In Europe, this task is covered by the European Civil Protection Mechanism (ECPM, http://ec.europa.eu/echo/what/civil-protection/mechanism_en ) which organizes and funds a series of drills in the field of civil protection in different member countries every year. The French example provides a good gauge for a national policy for crisis drills. With a concern for optimizing the response from stakeholders and the public in a crisis, the 2004 law on the modernization of civil security (law #2004–811 dated 13 August 2004) makes regular exercises compulsory, with a requirement for large-scale drills several times a year at national and regional levels (Richter-type earthquake drills are a good example) and a requirement for all towns and villages where a major natural or technological risk has been identified to conduct at least one crisis drill per year (DGSCGC or Direction Générale de la Sécurité Civile et de la Gestion des Crises, 2008). According to the guidelines set by the General Directorate for Civil Security and Crisis Management (DGSCGC), a body whose equivalent can be found in most countries, there are two main types of exercises (Institut National des Hautes Etudes de la Sécurité et de la Justice (INHESJ) 2015 ): “table-top exercises” (“exercices cadres”) and “field conditions exercises” (“exercices terrain”). The former are desk-based and take place at the crisis headquarters. They do not involve the deployment of any resources on the ground. Participants receive information by radio, phone, fax, television, SMS and the social networks. They are required to analyze, and synthetize this information, react, report to others, make propositions, set priorities and make choices to manage the crisis for the better. The second type involves the deployment of men and equipment on the ground. One of its objectives is to test the transportation and deployment of equipment in real-life and real-time conditions. Good examples of such activities include the exercises organized periodically in the US by the FEMA or those organized by area prefectures in France. For instance, the European Sequana 2016 exercise, held in March 2016 and which simulated the occurrence of a 100-year flood of the Seine in Paris, involving public stakeholders at various levels (national, zonal, departmental and municipal) and an array of private operators (transport firms, telecommunications companies, banks, supermarkets, hospitals, and so on). On the one hand, the goal of this exercise was to test Paris area regional stakeholders’ ability to coordinate and to cope with response and crisis management. On the other hand, that test was also an opportunity to assess the relevance of operators’ crisis management plans as well as the consistency of operational procedures. Eventually, public authorities were also provided with a feedback and the scope of information for population was measured for ensuring their awareness can be improved in the event of a disaster. The exercise uncovered two points to improve in the emergency response: the coordination of public and private actors, very heterogeneous according to the sectors of activity, and the information of the population, which sometimes lacked efficiency (some instructions have not been well assimilated) (Creton-Cazenave and November 2017 ). However, in France, in spite of these efforts, crisis exercises remain all too rare, especially at local level. In its 2012 activity report, the French Committee for Civil Defense (Haut Comité Français pour la Défense Civile (HCFDC) 2012 ) pointed out that in France “crisis management procedures are too often untested” for high-intensity events. In addition, such exercises, whether they are “table-top” or “in real conditions” exercises, take place at the initiative of major public institutions (government agencies, prefectures, civil protection departments) but are rarely if ever initiated by the research sector.

In this context, the CRISSIS program aimed to test the municipality’s current crisis management procedures (set in the December 2013 PCS) and help optimize them through two crisis exercises involving local stakeholders, organized and designed according to a principle of progressivity.

Methodology of program exercises

The first exercise took place at the start of the program in March 2015. It consisted in a simple training session aimed at informing the municipality’s senior administrative staff (Head of municipal police, Head of technical department, Director General of administration) of the main procedures and mechanisms listed in the Municipal Rescue Plan, which had recently been adopted. This session did not include the program’s findings on hazard analysis, vulnerability and population perceptions/representations. The training followed the format of a framework exercise, which was organized in Paris by students from the Master’s degree “Gestion Globale des Risques et des Crises” (“Global Risk and Crisis Management”, or GGRC), working from a low-intensity crisis scenario. In practice, the exercise ran over three hours and the participants broke out into two units: (i) a “facilitation” unit where the participants played the parts of Préfecture staff, firefighters, security forces, the media and the population, who were responsible for sending “inputs” based on the chosen scenario to (ii) the crisis unit that simulated the work of the municipal command team (PCC).

Following this first training session, a second, more ambitious exercise took place locally a year later, in March 2016 (duration: 3 h). This time, the exercise involved all the municipal staff including elected members of the Council, as well as senior representatives of the local authorities: the Préfecture of the Aude département (where Leucate is located), département managers of the fire brigade and the DDTM (“Direction de l’Aménagement et du Territoire”, or “Planning and Territorial Directorate”, a devolved State body in charge of risk prevention). This time, the session included both framework and field activities. Some elements were performed in a real-life setting (on-the-ground deployment of technical staff and municipal police forces) to test the coordination of the municipal crisis unit (municipal command team, or PCC), with resources deployed on the ground. However, because of financial and public security constraints, it was not possible to perform the entire exercise in real-life conditions: for instance, civil safety (firefighters) and security forces (gendarmerie) were not involved in real life but fictionally. Facilitators played the part of the media (television, press), the social networks, the population affected by the crisis and the private operators involved.

This time, the scenario included new data (on hazard and vulnerability) acquired during the project’s previous stages. The main objective was to test the “marine submersion” section of the PCS to which detailed specific and intermediary objectives had been added, as shown in Table  4 .

The scenario was entirely designed by the students of the GGRC Master’s degree from Université Paris 1, under the supervision of crisis exercise specialists, and with the assistance of two senior members of municipal staff (the Head of environment and a Municipal Police manager) as well as a manager from the Aude préfecture (deputy risk manager) who brought their field experience on board and helped develop credible “inputs”. The danger when creating such exercises is that participants might in retrospect challenge their credibility – for instance because they consider that their impact was too low or too high, or too remote from real-life situations. If this had been the case, the exercise would not have achieved its learning objective of consolidating the municipal staff’s knowledge of crisis management tools and procedures, and where possible helping improve them. It was therefore essential for this scenario to be developed in collaboration with individuals who had an excellent knowledge of local realities and institutions.

Stimuli were produced on two levels: (i) at Préfecture level, by staff based at the Interdepartmental Service of Defense and Civil Protection (Service Interdépartemental de Défense et de Protection Civile, SIDPC) of the Aude Préfecture in Carcassone (sent out emergency notifications from the Préfecture , responded to the municipality’s requests for additional resources); (ii) at municipal level, from a site in Leucate, by the students from the GGRC Master’s and by the town’s two contact persons (sent out all other “inputs”: reports of local damage caused by the storm, requests from the population, media queries, pressure on the social networks, etc.). The crisis was simulated on the evening of Saturday 9 April 2016 – that is, over a weekend during mid-tourist season (the week-end before a major sporting event organized in Leucate, the “Mondial du Vent”). During this period the town usually hosts 8000 to 10,000 people (for a permanent resident population of 5000) staying in secondary homes, campsites and camper van parks. Figure  2 shows an overview of the roll-out of the three-hour exercise, which has also been documented in a film that is available on the program website ( http://crissis2015.free.fr/ ).

Flowchart of the roll-out of the crisis exercise, March 2016. Source: ©Master GGRC, 2016 (PCC: municipal post of command; PREDICT: consultancy, service provider for the local authority; DEBEX: start of exercise; FINEX: end of exercise)

Results and discussion

Production of high-resolution marine submersion maps.

The validation of the digital modeling system and the multivariate statistical analysis of extreme values on record (see above) enabled us to elaborate several submersion scenarios. Simulations were run to characterize the spread and intensity of submersions for a hundred-year event (Nicolae et al. 2018 ), and to forecast the consequences of a gradual rise of the average sea level under the effect of climate change. For this purpose, we estimated the impact of a minor rise in sea level working from a variation of + 0.2 m (the average global rise forecasted according to the median scenario for the 2046–2065 period in comparison with 1986–2005 – source: IPCC WG1 Ch13, Church et al. 2013 ) and + 0.6 m (the average sea level rise forecasted in the Mediterranean by 2100, Slangen et al. 2014 ).

For the March 2016 crisis exercise, our consultation with the two members of municipal staff who contributed to the script drove us to simulate a coastal flood caused by a twenty-year storm, which combined the characteristics of the last two major storms (March 2013 and November 2014) in terms of wave height and sea levels – the former had caused the breach of a seafront wall in Leucate Plage, and the latter had provoked a flood by overtopping on the seafront and overflowing in Port Leucate (Fig.  3 ). The objective was therefore to engage the municipal staff in a role play using a scenario that combined events they might already have encountered, but separately. This helped ensure that the scenario had enough impact to place the players under pressure, while not being too “overblown”, which could have been the case with a simulation of a hundred-year storm that factored in the rise of the average sea level.

Submersion scenario, a Leucate Plage, b naturist village, c Port Leucate, created from the digital model and used for the March 2016 field exercise

Mapping out critical vulnerability levels

The analysis of vulnerability using the method described above enabled us to establish a vulnerability index (see Table II), which was mapped out to highlight the most vulnerable buildings and populations. For Leucate, three categories were defined and prioritized, ranging from low to medium and high vulnerability (Figs.  4 and 5 ).

Material vulnerability of people surveyed in Leucate (source: field survey)

Location of vulnerable populations based on age and health status (source: field surveys)

Spatial mapping makes it possible to draw comparisons within one single entity, but also between entities themselves, highlighting in this case a variation in levels of material vulnerability between areas. After assessing vulnerability, this ongoing study aims to recommend strategies to adapt buildings depending on their exposure to risk. This diagnosis will be expanded to the totality of buildings in risk areas. By globalizing vulnerability, we will thus be able to assess not only material vulnerability but also territorial vulnerability (D’Ercole and Metzger 2009 ).

These maps of vulnerability were integrated to the PCS as appendixes, and made available to participants for the second exercise in May 2016. Their purpose was, where possible, to inform the first protection measures taken by municipal staff during the crisis (for instance, setting up coffer dams), as well as the organization of evacuation.

A poor risk culture

Our analysis of perceptions and representations showed a poor awareness of coastal flood risk amongst surveyed populations. For instance, of all residents and tourists surveyed in areas that were shown by our model to be potentially submersible, only 50% of people surveyed declared that they were living in a risk area (Fig.  6 ).

Perceptions of residents on their property’s exposure to marine submersion risk

43% of first and second homeowners declared that the municipality of Leucate was not threatened by coastal floods. This finding is combined with an underestimation of risk. In comments recorded as annexes to the questions, some people who had been informed of past marine submersion events explained that they did not consider the few intrusions of sea water into the streets and houses as floods. According to these people, the hazard does not exist until there are human casualties, and material damage is considered unimportant and remediable. We also sought to find out whether residents were aware of the systems set up by the municipality to alert them in the event of a risk, including the volunteer-run SMS alert system outlined in the PCS. On this point, we found a significant difference between first home and second home owners: 34% of the former had communicated their contact details to the local authorities, while 74% of the latter were unaware of the existence of this system – and this despite the fact that of all second home residents surveyed, only 29% declared they were never present in Leucate between October and March (the high-risk period for coastal floods).

Consequently, it appears necessary to implement a communication strategy to inform the population, and in particular second-home owners, of existing emergency alerts. Although the findings of this study of perceptions/representations were not used in the March 2016 exercise, they informed the recommendations drafted in our exercise debrief notes to improve the municipality’s information, awareness raising and communication strategy.

Lessons learned from the exercise debrief: A poor integration of crisis management systems and procedures

An exercise debrief includes a methodical analysis of the exercise, to highlight its strong points and improvement points in order to perfect the organization’s crisis management processes. In this case, the scope of the lessons learned went beyond a sole technical fixing of failing tools or processes. The aim was to question individual and organizational responses to extreme event that might pose a challenge to the system (Lagadec 1993 ).

Our debrief from the first exercise (March 2015) revealed a poor knowledge of the Municipal Rescue Plan (PCS) on the part of municipal staff, and helped us present a few observations on its contents. For instance, the PCS had no objective quantifiable milestones (in meters) regarding the water levels attained in submersed areas: the decision to activate the successive phases of the PCS (closing roadways, evacuating certain neighborhoods) were only based on field information communicated by technical staff who have been working for the municipality for years and therefore have an in-depth knowledge of local sites. However this lack of quantifiable milestones can be a disadvantage for inexperienced staff (for instance people who are new in post, or covering for more experienced permanent staff members who might be off work when a crisis occurs), leading to damaging delays in a context of emergency crisis management. Following these observations, the municipality of Leucate introduced geo-referenced flood markers into its PCS and committed to fully participating in the second exercise to improve municipal staff’s command of the PCS.

The debrief for the second exercise (March 2016) was captured in a report that was presented in early May 2016 to all municipal staff. It highlighted the municipal teams’ excellent field knowledge, as well as a good coordination between the municipal post of command (PCC) and the teams deployed on the ground. However, it also revealed the municipal staff’s obvious lack of knowledge of the PCS: most staff had no clear understanding of their respective roles and responsibilities within the crisis unit, and therefore faced difficulties in organizing and coordinating the PCC. Furthermore, these challenges were aggravated by the crisis headquarters’ lack of practicality: the functions of secretariat, command, logistics and coordination were all gathered in a single room, which caused a great deal of confusion. In this context, the fear of an error was a major source of stress, causing communication challenges both internally within the crisis unit (absence of situation updates) and externally (communication with Préfecture services and the media). Consequently, the debrief report included four main recommendations:

Reorganizing the PCC according to the traditional organizational structure of a crisis unit, to facilitate communication and decision-making in the event of a crisis. The space should be split into five open units (Fig.  7 ): decision-making and coordination unit; situation unit (secretariat/log); logistical unit; communication unit; forecasting unit)

Example of proposed reorganization of the PCC suggested in the exercise debrief report

Drafting concise post descriptions to be included into the PCS, so that from the moment of their arrival into the PCC each member of the crisis unit knows what their role is and what they are expected to do. Examples of post descriptions: crisis unit Director (DOS); unit Coordinator (needs to be very mobile and move between units); Secretary (keeping a log, handling calls); communication unit / forecasting unit / logistical unit Managers.

Writing a checklist to be inserted at the start of the PCS, outlining the key principles of crisis management: sharing the logbook; updating the schedule and map in real time; regular situation updates, and communication of human casualties to the higher echelons ( Préfecture ), etc.

In addition, the municipality should improve its communication with the population ahead of the crisis (for instance via the local news bulletin) on current crisis alert systems and in particular the SMS alert (this recommendation directly derives from the analysis of perceptions/representations of risk).

Discussion: What are the obstacles faced by an operational approach to coastal flood risk?

The resolutely operational approach adopted by the CRISSIS program faced three challenges. First of all, it has been difficult to convince local representatives to organize a crisis exercise locally. While the first exercise, which took place in Paris in March 2015, did not pose any major issues as its stakes were lower (low-intensity exercise, remote location, framework exercise only, involving only two technical staff members and the Director General of municipal services as observers), organizing the second proved markedly more complex. As this exercise needed to take place locally and involve large numbers of Council members and municipal staff, we were initially faced with a clear reluctance on their part. Eventually, only two Council members (two Deputy Mayors) did take part in the exercise, along with about twenty administrative and technical staff members. The 2004 Law for the modernization of civil security (Act 2004–811 of 13 August 2004) states that any municipality where at least one major natural or technological risk has been identified must organize at least one crisis exercise per year (DGSCGC, 2008). However, as highlighted by the French Committee for Civil Defense in its 2012 report (Haut Comité Français pour la Défense Civile (HCFDC) 2012 ), very few municipalities actually comply with this obligation. This reluctance may be due to the lack of municipal resources, or perhaps to the fear of being evaluated and judged. In this respect, a lot of educational work is needed to convince potential participants that the objective of such exercises is not to evaluate individuals but systems and procedures, in order to improve them and make them easier to memorize. Only when the exercise was completed did participants finally drop their guard and admit to its usefulness.

In addition, municipal staff made a variable use of the operational documents (maps) presenting the findings of the analysis of hazards and vulnerability. The submersion forecast maps that were provided to the PCC coordinator (Head of the municipal police) at various points during the crisis, in replacement for the maps he would normally had received from hydro-meteorological experts Predict (the municipality’s current service provider) were used properly. However, this was not the case with the maps showing people and buildings’ critical vulnerability levels, which could have informed the first protection measures (for instance, setting up coffer dams) taken by personnel on the ground. This challenge shows the necessity of providing the PCC staff with user-friendly documents that can be read quickly. Similar observations had been made during the crisis exercise organized for a group of municipalities in La Réunion by students from the École des Mines in Alès as part of the only other French program on submersion risk (Wassner et al. 2016 ) that also included an operational dimension and a crisis exercise.

Finally, the actual adoption of the recommendations presented in the exercise debrief report is a very long-term process. Although these recommendations were approved by the municipality when the report was first presented to them, over a year on only the first has led to concrete action being taken (the reorganization of the PCC). The PCS has still not been modified. Besides, this plan has never been tested in real-life conditions (as the last storm occurred in November 2014, before its adoption): it still remains unsure whether the municipality does have the capacity to tackle a high-intensity storm. The most “extreme” scenarios tested as part of the project’s hazard analysis show for instance that the spread and volume of the flood would increase by respectively 160% and 188% in the event of a hundred-year storm with a 0.6 rise of sea level (Nicolae et al. 2018 , Anselme et al. 2017 ). Just as it is necessary to implement a robust prevention policy (the Submersion Risk Prevention Plan for Leucate was approved in January 2017), improving crisis management procedures should also be a priority for the municipality in the years to come.

The initial objective of the CRISSIS program was to improve both the anticipation of risk and the implementation of adapted responses to better tackle its unpredictability and help with decision-making, in the context of a highly urbanized municipality that is periodically impacted by sea water floods (inundation, barrier overtopping, breaching of barriers). To achieve this, our research focused simultaneously on the natural (hazard), material and social (vulnerability, perception/representations) dimensions of risk. However, the objective was also to engage with local authorities by inviting them to work on the operational aspect of crisis management, which is usually neglected by research programs on flood risk. In this perspective, we worked to improve the various stakeholders’ operational response by using crisis exercises to assess the degree to which they had adopted the tools and systems placed at their disposal (PCC, PCS), but also by helping improve these tools and systems using the new findings produced by the program’s first three sections.

Overall, this project helped improve our understanding of submersible areas and create maps of critical vulnerability, both material and human. It also revealed the poor social representation of marine submersion risk, as well as a clear lack of awareness of crisis management systems and tools, and of behaviors that should be adopted in the event of a flood. These findings highlight the need for setting up a communication strategy, to raise awareness of risk and inform the population of current alert mechanisms. The crisis exercise conducted in March 2016 with relevant municipal departments showed the importance of creating such exercises working from a realistic scenario, to ensure that all staff in positions of responsibility are aware of procedures, but also to detect any potential gaps in the contents of the PCS. In a context where hazard and vulnerability are bound to become more extreme, this should be a key action in the necessary optimization of crisis management systems and procedures.

Anneli, J.F. 2006. 2006, the National Incident Management System: A multi-agency approach to emergency response in the United States of America. Rev. sci. tech. Off. int. Epiz. 25 (1): 223–231.

Article   Google Scholar  

Anselme, B., P. Durand, Y.F. Thomas, and A. Nicolae-Lerma. 2011. Storm extreme levels and coastal flood hazards. A parametric approach on the french coast of languedoc (district of Leucate). Comptes Rendus Geosciences 343 (10): 677–690.

Anselme, B., P. Durand, Y.F. Thomas, and A. Nicolae-Lerma. 2017. Coastal flood Hazard. Risk and crisis management : Questions raised by sea level rise ? 10–14. New York: International WRCP/IOC Conference, (poster) Columbia University.

Google Scholar  

Baggio, S., and M.-L. Rouquette. 2006. La représentation sociale de l’inondation : influence croisée de la proximité au risque et de l’importance de l’enjeu. Bulletin de Psychologie 59 (1): 103–117.

Barroca B., Pottier N., Lefort E . , 2005, Analyse et évaluation de la vulnérabilité aux inondations du bassin de l’Orge aval. Actes des septièmes rencontres de TheoQuant, Atelier 3 « Risques, vulnérabilité » , Besançon, 12p.

Becerra, S. 2012. Vulnérabilité, risques et environnement : l’itinéraire chaotique d’un paradigme sociologique contemporain. VertigO - la revue électronique en sciences de l’environnement [En ligne] 12 (1). URL : http://vertigo.revues.org/11988 ). https://doi.org/10.4000/vertigo.11988 .

Booij, N., R.C. Ris, and L.H. Holthuijsen. 1999. A third-generation wave model for coastal regions, part I: Model description and validation. Journal of Geophysical Research 104 (C4): 7649–7666.

Cariolet, J.-M., S. Suanez, C. Meur-Férec, and A. Postec. 2012, 2012. URL : https://journals.openedition.org/cybergeo/25077 . Cartographie de l’aléa de submersion marine et PPR : éléments de réflexion à partir de l’analyse de la commune de Guissény (Finistère, France). Cybergeo : European Journal of Geography [En ligne] , Espace, Société, Territoire, document 586, mis en ligne le 02 février. https://doi.org/10.4000/cybergeo.25077 .

Chauveau, E., C. Chadenas, B. Comentale, P. Pottier, A. Blanlœil, T. Feuillet, D. Mercier, L. Pourinet, N. Rollo, I. Tillier, and B. Trouillet. 2011. Xynthia : leçons d’une catastrophe. Cybergeo : European Journal of Geography [En ligne] , Environnement, Nature, Paysage, document 538, mis en ligne le 09 juin 2011. URL : https://journals.openedition.org/cybergeo/23763 . https://doi.org/10.4000/cybergeo.23763 .

Church, J.A., P.U. Clark, A. Cazenave, J.M. Gregory, S. Jevrejeva, A. Levermann, M.A. Merrifield, G.A. Milne, R.S. Nerem, P.D. Nunn, A.J. Payne, W.T. Pfeffer, D. Stammer, and A.S. Unnikrishnan. 2013. Sea level change. In Climate change 2013: The physical science basis . Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, ed. T.F. Stocker, D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex, and P.M. Midgley, 1137–1216. Cambridge: Cambridge University Press. https://doi.org/10.1017/%20CBO9781107415324.026 .

Chapter   Google Scholar  

Creton-Cazenave, L., and V. November. 2017. La gestion de crise à l’épreuve de l’exercice. EU SEQUANA , La documentation française, 240:237 p.

D’Ercole, R., and P. Metzger. 2009. La vulnérabilité territoriale : une nouvelle approche des risques en milieu urbain, Cybergeo. European Journal of Geography [En ligne] , Dossiers, document 447, mis en ligne le 31 mars 2009, consulté le 14 octobre 2016. URL : https://journals.openedition.org/cybergeo/22022 . https://doi.org/10.4000/cybergeo.22022 .

D’Ercole, R., J.-C. Thouret, O. Dolfus, and J.-P. Asté. 1994. Les vulnérabilités des sociétés et des espaces urbanisés : concepts, typologie, modes d’analyse. Revue de géographie alpine , tome 82, n°4: 87–96.

Daniels, R.J., D.F. Kettl, and H. Kunreuther. 2011. On risk an disaster: Lessons from hurricane Katrina , Philadelphia: University of Pensylvania Press, 304 p.

DREAL de bassin Rhône-Méditerranée, 2016, Plan de gestion des risques inondations , bassin Rhône-Méditerranée , 2016–2021, vol 2, 295 p.

Duan, W., B. He, K. Takara, P. Luo, M. Hu, N.E. Alias, and D. Nover. 2015. Changes of precipitation amounts and extremes over Japan between 1901 and 2012 and their connection to climate indices. Clim Dynam 45: 2273–2292.

Duan, W., B. He, K. Takara, P. Luo, M. Hu, N.E. Alias, et al. 2014. Climate change impacts on wave characteristics along the coast of Japan from 1986 to 2012. Journal of Coastal Research 68: 97–104.

Egli, D.S. 2013. Beyond the storms. Strengthning preparedness, Response & Resilience in the 21 st century. Journal of Strategic Security 6 (2): 32–45.

Flanquart, H. 2014. Perception versus représentation du risque de submersion et autres risques : ce que révèle une querelle sémantique, In Connaissance et compréhension des risques côtiers : aléas, enjeux, représentations, gestion, actes de colloque , 3-4 juillet 2014, Université de Bretagne occidentale, Brest, 353–364.

Gallien, T.W., B.F. Sanders, and R.E. Flick. 2014. Urban coastal flood prediction: Integrating wave overtopping, flood defenses and drainage. Coastal Engineering 91: 18–28. https://doi.org/10.1016/j.coastaleng.2014.04.007 .

Genovese, E., S. Hallegatte, and P. Dumas. 2011. Damage assessment from storm surge to coastal cities: Lessons from the Miami area. In Advancing Geoinformation Science for a Changing World. Lecture Notes in Geoinformation and Cartography , (eds). Geertman S., Reinhardt W., Toppen F. vol 1. 21–43. Berlin, Heidelberg: Springer.

Genovese, E., and V. Przyluski. 2013. Storm surge disaster risk management : The Xynthia case study in France. Journal of Risk Research 16(7):825–841.

Goeldner-Gianella L., Chionne D., 2014, Des enquêtes sociales sur les savoirs, les pratiques et les comportements face aux risques littoraux, Colloque international Réduire les risques littoraux et s’adapter au changement climatique , La Rochelle, 2-4 Avril 2014. https://lienss.univ-larochelle.fr/IMG/pdf/actes_colloque_la_rochelle_2-4_avril_2014.pdf .

Guimarães, P.V., L. Farina, E. Toldo Jr., G. Diaz-Hernandez, and E. Akhmatskaya. 2015. Numerical simulation of extreme wave runup during storm events in Tramandaí Beach, Rio Grande do Sul, Brazil. Coastal Engineering 95: 171–180. https://doi.org/10.1016/j.coastaleng.2014.10.008 .

Haut Comité Français pour la Défense Civile (HCFDC), 2012, Risques et menaces exceptionnels. Quelle préparation ? , Rapport d’activité 2011, 139p.

Hellequin, A.-P., C. Meur-Férec, H. Flanquart, and B. Rulleau. 2013. Perceptions du risque de submersion marine par la population locale du littoral languedocien : contribution à l’analyse de la vulnérabilité côtière. Natures Sciences Sociétés 21 (4): 385–399.

Institut National des Hautes Etudes de la Sécurité et de la Justice (INHESJ), 2015. La gestion de crise en Europe. In Vers une coexistence des organisations actuelles basée sur la culture des états membres ou vers une convergence structurelle dans un système européen? Rapport de la 26ème session « Sécurité et Justice » 2014–2015, Groupe de Sécurité stratégique, Paris, 147 p.

Krien N., 2014, Place des risques côtiers dans la représentation du cadre de vie d’individus possédant des enjeux sur des communes « à risque », thèse de l’Université de Bretagne occidentale, 237p.

Lagadec P., 1993, Apprendre à gérer les crises - société vulnérable, acteurs responsables, Editions d’Organisation, 120p.

Lagadec P., 2001, Les exercices de crise : pour des ruptures créatrices , La lettre des cindyniques, n° 34 .

Lagadec, P. 2004. Understanding the French 2003 heat wave experience: Beyond the heat, a multi-layered challenge. Journal of Contengencies and Crisis Management 12 (4): 160–169.

Lagadec, P. 2012. Du risque majeur aux mégachocs. Dossier spécial : la gestion de crise, méthodologies et retours d’expérience, Sécurité et stratégie 10: 50–52.

Lagahé, E., and F. Vinet. 2014. Evaluation de la vulnérabilité des logements face à la submersion sur l’île d’Oléron, Rapport de projet Risks , 103. Île d’Oléron: UMR Liens Université de la Rochelle, PAPI.

Lazure, P., and F. Dumas. 2008. An external–internal mode coupling for a 3D hydrodynamical model for applications at regional scale (MARS). Advances in Water Resources 31: 233–250.

Le Roy, S., R. Pedreros, C. André, F. Paris, S. Lecacheux, F. Marche, and C. Vinchon. 2015. Coastal flooding of urban areas by overtopping: Dynamic modelling application to the Johanna storm (2008) in Gâvres (France). Natural Hazards and Earth System Sciences 15: 2497–2510. https://doi.org/10.5194/nhess-15-2497-2015 .

Leone F., 2007, Caractérisation des vulnérabilités aux catastrophes « naturelles » : contribution à une évaluation géographique multirisque (mouvements de terrain, séismes, tsunamis, éruptions volcaniques, cyclones) – HDR de l’Université Paul Valéry Montpellier 3, 244 p. + annexes.

Leone F., Asté J-P., Leroi E., 1996, L’évaluation de la vulnérabilité aux mouvements de terrains : pour une meilleure quantification du risque, Revue de géographie alpine , tome 84, n°1, pp. 35–46. https://doi.org/10.3406/rga.1996.3846 . http://www.ano-omiv.cnrs.fr/images/Publications/PDFs/MasAvignonet/JournalManuscripts/1996-Leone_evaluation.pdf .

Meur-Ferec C., Flanquart H., Hellequin A.P., Rulleau B., 2011, Risk perception, a key component of systemic vulnerability of coastal zones to erosion-submersion. Case study on the French Mediterranean coast. Littoral 2010 - Adapting to Global Change at the Coast: Leadership, Innovation and Investment 2011 , Royaume-Uni (2010), 8p.

Nicolae, Lerma A., S. Elineau, T. Bulteau, F. Paris, P. Durand, B. Anselme, and R. Pedreros. 2018. High resolution flood modeling coupling overflowing and overtopping process, framing the hazard based on historical and statistic approach. Natural Hazards and Earth System Sciences 18: 207–229. https://doi.org/10.5194/nhess-18-2017-2018 .

Nicolae, Lerma A., S. Elineau, F. Paris, Y. Balouin, S. Lecacheux, P. Durand, B. Anselme, E. Longepe, S. Defossez, and Gianella L. Goeldner. 2015. Modélisation numérique de l’aléa de submersion appliquée à l’élaboration des plans d’évacuation et à la gestion de crise, exemple de la commune de Leucate . Ferrare: Paralia, In: Actes 3rd Coastal And Maritime Mediterranean Conference.

Pont C., 2015, Aborder et caractériser le risque de submersion marine sur les littoraux sableux méditerranéens : l’exemple de la commune de Leucate, mémoire de master, université Paris 1 Panthéon Sorbonne, 150 p.

Reghezza Zitt, M., and S. Rufat. 2015. Résiliences. Sociétés et territoires face à l’incertitude, aux risques et aux catastrophes , 226. London: ISTE Editions.

Ruin I., 2010, Conduite à contre-courant et crues rapides, le conflit du quotidien et de l’exceptionnel, Annales de la Géographie , v4, n°674, p. 419–432.

Samuels, P., Huntington S., Allsop W., Harrop W., 2008, Flood risk management : Research and Practice. Proceedings of the European conference on flood risk management research into practice (Floodrisk 2008), Oxford, extended abstracts volume, 332 p.

Book   Google Scholar  

Slangen, A.B.A., M. Carson, C.A. Katsman, R.S.W. van de Wal, A. Köhl, L.L.A. Vermeersen, and D. Stammer. 2014. Projecting twenty-first century regional sea-level changes. Climatic Change 124 (1): 317–332.

Article   CAS   Google Scholar  

Sorensen, C., M. Jebens, and T. Piontkowitz. 2017. Danish risk management plans of the EU flood directive. La Houille Blanche, n° 4: 31–39.

Stern, E. 2014. Designing Crisis Management Training and Exercises for Strategic Leaders. A Swedish and United States Collaborative Project. , 112. Stockholm: Swedish National Defense College, Elanders Sverige AB.

Thouret, J.-C., and R. D’Ercole. 1996. Vulnérabilité aux risques naturels en milieu urbain : effets, facteurs et réponses sociales. Cahiers des sciences humaines, ORSTOM 32 (2): 407–422.

Ullmann, A. 2009. Changement climatique et évolution des tempêtes dans le Golfe du Lion : approche par intégration d’échelles spatio-temporelles. Cybergeo : European Journal of Geography [En ligne] , Environnement, Nature, Paysage, document 441, mis en ligne le 18 mars 2009, consulté le 25 janvier 2017. URL : https://journals.openedition.org/cybergeo/22013 . https://doi.org/10.4000/cybergeo.22013 .

Vinchon C., Baron-Yelles N, Berthelier E., Hérivaux C., Lecacheux S., Meur-Ferec C., Pedreros R., Rey-Valette H., Rulleau B., 2011, MISEEVA: Set up of a transdisciplinary approach to assess vulnerability of the coastal zone to marine inundation at regional and local scale, within a global change context, Littoral 2010 – Adapting to Global Change at the Coast: Leadership, Innovation, and Investment, London 21-23 September 2010, 10p.

Wassner T.S., Sauvagnargues, P.A. Ayral, F. Tena-Chollet, N. Frealle, 2016. Retour sur l’exercice de simulation de crise au sein du simulateur de l’école des mines d’Alès , rapport WP4 - D4 - 3a, projet ANR SPICy "Système de prévision des inondations côtières et fluviales en contexte cyclonique", 142 p.

Yates-Michelin M., Le Cozannet G., Balouin Y., 2011, Etat des connaissances sur les effets potentiels du changement climatique sur les aléas côtiers en région Languedoc-Roussillon , rapport final BRGM/RP 58 872- FR, 83p., 26 III., 2 annexes.

Zijlema M., Stelling G., Smit P., 2011, “SWASH: An operational public domain code for simulating wave fields and rapidly varied flows in coastal waters”.

Download references

Acknowledgements

We would like to thank the Conseil Supérieur de la Formation et de la Recherche Stratégiques (CSFRS) for funding this research program. Our thanks also go to the municipality of Leucate who volunteered to take part in this program and greatly facilitated our work on the ground.

This research work was supported by the French Conseil Supérieur de la Formation et de la Recherche Stratégiques (CSFRS), within the framework of the call for non-thematic projects 2012. The funding body has played no role in the design of the study, the collection, analysis and interpretation of data, or the writing of the manuscript.

Author information

Authors and affiliations.

Université Paris 1 Panthéon-Sorbonne, 191 rue Saint Jacques, F-75005, Paris, France

Paul Durand, Brice Anselme & Lydie Goeldner-Gianella

Laboratoire de Géographie Physique, UMR 85911 place Aristide Briand cedex, F-92195, Meudon, France

Paul Durand, Sylvain Elineau & Lydie Goeldner-Gianella

Pôle de Recherche pour l’Organisation et la Diffusion de l’Information Géographique, UMR 8586 2 rue Valette, F-75005, Paris, France

Brice Anselme

Université Paul Valéry, 2 rue du Professeur Henri Serre, 34080, Montpellier, France

Stéphanie Defossez & Monique Gherardi

UMR GRED – IRD (Gouvernance, Risque, Environnement, Développement), route de Mende, 34199, Montpellier, France

BRGM, 3 Avenue Claude Guillemin, 45100, Orléans, France

Sylvain Elineau & Alexandre Nicolae-Lerma

Centre universitaire de formation et de recherche de Mayotte, Dembéni, Mayotte

Esméralda Longépée

UMR Espace Dev, 500 rue JF Breton cedex 5, 34093, Montpellier, France

You can also search for this author in PubMed   Google Scholar

Contributions

BA CRISSIS program manager, manuscript’s redaction: intro, conclusion, study area, figures design and layout. PD preparation of crisis simulation exercises, manuscript’s redaction: general structure of the paper, intro, conclusion, method, results and discussion (crisis exercises). ALN and SE numerical modeling, manuscript’s redaction: method, results and discussion (hazard). SD and MG vulnerability survey, vulnerability index design, manuscript’s redaction: method, results and discussion (vulnerability mapping). LG-G and EL survey ’ s conception, survey in the field, statistical treatment, survey ’ s analysis method, results and discussion (risk perceptions and representations). All authors read and approved the final manuscript.

Corresponding author

Correspondence to Brice Anselme .

Ethics declarations

Ethics approval and consent to participate.

Not applicable

Consent for publication

Competing interests.

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/ ), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Reprints and permissions

About this article

Cite this article.

Durand, P., Anselme, B., Defossez, S. et al. Coastal flood risk: improving operational response, a case study on the municipality of Leucate, Languedoc, France. Geoenviron Disasters 5 , 19 (2018). https://doi.org/10.1186/s40677-018-0109-1

Download citation

Received : 04 May 2018

Accepted : 03 October 2018

Published : 29 October 2018

DOI : https://doi.org/10.1186/s40677-018-0109-1

Share this article

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Coastal flood risk
• Numerical modeling
• Vulnerability
• Risk perception
• Crisis exercise

• Air Pollution
• Architecture
• Bioengineering
• Boundary Elements
• Computational Methods for Engineering
• Damage & Fracture Mechanics
• Design & Nature
• Earthquake Engineering
• Electrical Engineering & Electromagnetics
• Environmental Engineering
• Environmental Health
• Fluid Mechanics
• Heat Transfer
• Historical Interest
• Information Systems
• Marine & Offshore Engineering
• Materials & Manufacturing
• Mathematics & Statistics
• Risk and Security
• Structural Engineering
• Sustainable Development
• Transport Engineering
• Urban Development
• Water Resources
• International Journals
• International Journal of Computational Methods and Experimental Measurements
• International Journal of Design & Nature and Ecodynamics
• International Journal of Ecodynamics
• International Journal of Energy Production and Management
• International Journal of Environmental Impacts
• International Journal of Heritage Architecture
• International Journal of Safety and Security Engineering
• International Journal of Sustainable Development and Planning
• International Journal of Transport Development and Integration
• Transactions of the Wessex Institute

WIT Transactions on Engineering Sciences

• WIT Transactions on The Built Environment
• WIT Transactions on Information and Communication Technologies
• WIT Transactions on Ecology and the Environment
• WIT Transactions on Modelling and Simulation
• WIT Transactions on Biomedicine and Health
• WIT Transactions on State-of-the-art in Science and Engineering
• About WIT Press
• About the Wessex Institute
• Frequently Asked Questions
• Obituary - Professor Carlos A Brebbia
• Privacy Policy
• Returns Policy
• WIT Transactions
• WIT Transactions Editorial Board
• Publish with WIT Press
• Submit a Conference Paper

Risk Analysis XI

COASTAL FLOODING: DAMAGE CLASSIFICATION AND CASE STUDIES IN CALABRIA, ITALY

Related conference

Short Course on Disaster and Resilience 2023

12-13 September 2023

New Forest, UK

Related Book

Edited By: S. Mambretti, Polytechnic of Milan, Italy; A. Fabbri, University of Milano-Bicocca, Italy

Transaction

10.2495/RISK180081

ANTONELLA NUCERA, GIANDOMENICO FOTI, CATERINA CANALE, PIERFABRIZIO PUNTORIERI, FRANCESCA MINNITI

Coastal flooding is a topic of particular interest both in scientific research and for public administration. In fact, effective management of both coastal erosion and coastal flood risk requires a mapping of flooding areas by current European legislation (Directive 2007/60/EC). Regarding Italy, coastal erosion is widely studied and mapped, but coastal flooding has not been uniformly examined across all regions. This paper analyses the main factors that influence coastal flooding, being mainly tidal excursion and run-up, and a new methodology is proposed for the classification of storm damage based on the effects produced by the coastal wave action. In fact, six classes of damage have been defined, sorted by increasing severity, namely: traffic interruption, infrastructure damage, maritime works damage, erosion of beaches and dunes, flooding to homes, and a combination of these various factors. The new classification was applied to two case studies, both in Calabria (Italy): Scilla on the Tyrrhenian coast, and Monasterace on the Ionian coast. The two locations were chosen because in Scilla the coastal morphology makes it particularly subject to storms that overreach the beach and reach local houses, even those located upstream of the seafront. In Monasterace, on the other hand, there is an important archaeological site on a coastal dune that, over the years, has often been damaged by sea storms. The analysis of the events was conducted starting with data present in the A.Si.Cal. (Historically flooded areas in Calabria) of the CNR-IRPI of Cosenza, which containing data relating to events of hydrogeological instability, including sea storms which have occurred in Calabria over the last few centuries, and from the MeteoCean group of the University of Genoa, which contains wave data for the period 1979–2017, which is reconstructed from the Climate Forecast System Reanalysis (CFSR) data.

coastal flooding, coastal management, damage classes, storm, tide, run-up, set-up

Other papers in this volume

HOW CREDIBLE IS MY HAZARD MAP? DISSECTING A PREDICTION PATTERN OF LANDSLIDE SUSCEPTIBILITY

A STUDY OF THE COMBINATION OF RISK ANALYSIS WITH A CITYWIDE LANDSLIDE EARLY WARNING SYSTEM

RESPONSE OF A LEBANESE ROCK-FILLED DAM TO SEISMIC EXCITATION

A MULTI-AGENT SYSTEM APPROACH IN EVALUATING HUMAN SPATIO-TEMPORAL VULNERABILITY TO SEISMIC RISK USING SOCIAL ATTACHMENT

STOCHASTIC CHARACTERISTIC OF SITE AMPLIFICATION FACTOR AND ITS EFFECT ON EARTHQUAKE GROUND MOTION

METHODOLOGICAL FRAMEWORK TO INTEGRATE SOCIAL AND PHYSICAL VULNERABILITY IN THE PREVENTION OF SEISMIC RISK

POLICY DIFFUSION IN COMMUNITY-SCALE FLOOD RISK MANAGEMENT

Keep me updated

WIT Press, Ashurst Lodge, Ashurst, Southampton SO40 7AA, UK. Registered in England as a limited company No. 4741634

Copyright 2024 WIT Press All Rights Reserved - Prices are Subject to Change - Returns Policy - Privacy Policy - Site Map

ORIGINAL RESEARCH article

Coastal flooding in the maldives induced by mean sea-level rise and wind-waves: from global to local coastal modelling.

• 1 Instituto Mediterráneo de Estudios Avanzados (UIB-CSIC), Esporles, Spain
• 2 Departament de Física, Universitat de les Illes Balears, Palma, Spain
• 3 French Geological Survey (BRGM), Orléans, France
• 4 Global Climate Forum, Berlin, Germany
• 5 Ministry of Environment, Malé, Maldives

The Maldives, with one of the lowest average land elevations above present-day mean sea level, is among the world regions that will be the most impacted by mean sea-level rise and marine extreme events induced by climate change. Yet, the lack of regional and local information on marine drivers is a major drawback that coastal decision-makers face to anticipate the impacts of climate change along the Maldivian coastlines. In this study we focus on wind-waves, the main driver of extremes causing coastal flooding in the region. We dynamically downscale large-scale fields from global wave models, providing a valuable source of climate information along the coastlines with spatial resolution down to 500 m. This dataset serves to characterise the wave climate around the Maldives, with applications in regional development and land reclamation, and is also an essential input for local flood hazard modelling. We illustrate this with a case study of HA Hoarafushi, an atoll island where local topo-bathymetry is available. This island is exposed to the highest incoming waves in the archipelago and recently saw development of an airport island on its reef via land reclamation. Regional waves are propagated toward the shoreline using a phase-resolving model and coastal inundation is simulated under different mean sea-level rise conditions of up to 1 m above present-day mean sea level. The results are represented as risk maps with different hazard levels gathering inundation depth and speed, providing a clear evidence of the impacts of the sea level rise combined with extreme wave events.

1. Introduction

Increased coastal flooding damages are among the potentially most hazardous and costliest aspects of global warming ( Hinkel et al., 2014 ), impacting populations, ecosystems and assets. Coastal flood exposure is currently increasing at rates higher than inland due to population growth, urbanisation and the coastward migration of people ( Merkens et al., 2018 ), and also due to coastal extreme water levels being raised by mean sea-level rise ( Marcos and Woodworth, 2017 ). The Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) of the Intergovernmental Panel on Climate Change (IPCC) projects that if greenhouse gas (GHG) emissions continue to rise unmitigated (i.e., RCP8.5) global-mean sea levels are likely to rise by 0.6–1.1 m by 2100, and 2.3–5.4 m by 2300 ( Oppenheimer et al., 2019 ). Projected mean sea-level rise during the twenty-first century and beyond ( Kopp et al., 2014 ) will inevitably increase the intensity of flood events and will thus exacerbate the exposure and vulnerability of coastal areas in the decades to come, with highest impacts expected in low-lying regions. Hinkel et al. (2014) estimated that, without adaptation, by 2100 almost 5% of the global population will be potentially flooded annually, with losses of up to 10% of the global GDP, under a 1.20 m mean sea-level rise. This will require the implementation of extensive and ubiquitous coastal adaptation solutions to avoid such large impacts ( Hinkel et al., 2019 ). But also if emissions are reduced to meet the goal of the Paris Agreement to limit global warming “well bellow 2°C” (i.e., RCP2.6), global mean sea-level is likely to rise by 0.3–0.6 m in 2100 and 0.6–1.1 m by 2300, which will still be a tremendous challenge, in particular for very low lying regions such as atoll states.

The threats of flooding events are particularly worrisome in low-lying coastal zones, including large deltas and sinking coastal mega-cities; but the regions with the largest expected relative impacts are small island states ( Nurse et al., 2014 ). The Maldivian archipelago is an iconic case of vulnerability to mean sea-level rise. Located in the equatorial region of the Tropical Indian Ocean, the Maldives consist of 1192 islands, dispersed across 860 km from 8° north to 1° south in latitude, of which 188 are inhabited ( NBS, 2017 ; Wadey et al., 2017 ) (see Figure 1 ). The resident population in 2014 was 437,000 people and is estimated to reach 557,000 in 2020, with 40% of the population living in the capital, Malé, and its surrounding islands Villimalé and Hulhumalé ( NBS, 2019 ). Average land elevations range from 0.5 m to 2.3 m above present-day mean sea level ( Woodworth, 2005 ), with 80% falling below 1 m. Since the 1950s several land reclamation projects have been carried out to address land scarcity, for example in the southern lagoon of Malé in 1954 ( Maniku, 1990 ). With the rapid economic development of the Maldives, land reclamation projects have also increased. The Maldivian government estimates that over 1300 hectares of reef or lagoon area have been reclaimed up until 2016 ( MEE, 2017 ). This new land is required to be elevated between 1.5 and 1.75 m above mean sea-level. However, this static approach to island elevation ignores the differing wave exposure across the archipelago.

Figure 1 . Map of the Indian Ocean with the Maldivian archipelago inside the black box. The four black arrows indicate the main wave direction identified. The red arrow indicates the location of the Haa Alif atoll in which is located Hoarafushi island (satellite image in the bottom-right corner extracted from Google Earth. Image © 2019 Maxar Technologies; Image © 2019 CNES/Airbus; Data SIO, NOAA, U.S. Navy, NGA, GEBCO).

A lot of land reclamation is taking place in the Maldives and a new long-term regional development strategy is currently being prepared that prioritises islands for development ( Gussmann and Hinkel, 2021 ). While it is known that wave exposure differs across islands, this has so far not been taken into account in land reclamation and regional development. The development of adaptation plans in the framework of coastline management aimed to address flood hazards requires accurate information and a deep understanding of the driving processes. Coastal flood events are caused by extreme coastal water levels that in turn result from the combination of relative mean sea-level, tides, storm surges, wind-waves, precipitation and/or river run-off ( Woodworth et al., 2019 ). The design of adaptation strategies therefore involves the knowledge of every individual driver and their future projections at the local scale, as well as their possible interactions ( Nicholls et al., 2014 ). In the case of the Maldives, the tidal range is relatively small (<1 m of maximum high waters) and the storm surge contribution is negligible, as corresponds to an equatorial region ( Wadey et al., 2017 ). Earlier studies have pointed at wind-waves as the primary mechanism causing flooding events in the Maldives, similarly to other Indian and Pacific islands ( Hoeke et al., 2013 ). One of the first works was presented by Harangozo (2013) , who investigated an event that occurred in April 1987 that flooded Mal?é, including reclaimed land below 1 m above mean sea-level and during which the hard structures designed to protect this land were destroyed. Based on altimetric wave measurements and in-situ sea-level observations, this event was attributed to prolonged swell waves originated in the Southern Indian Ocean and reaching the island during high tides. Similarly, in 2007, the Fares island, located in the southernmost atoll of the Maldives was flooded due to a series of remotely-generated swell events reaching the island ( Wadey et al., 2017 ; Beetham and Kench, 2018 ) which also affected other areas of the eastern Indian Ocean (e.g., Lecacheux et al., 2012 in La Réunion Island). This event was particularly hazardous as it flooded almost the entire island and affected more than 1500 people as well as the limited water resources of the island. An extensive study was carried out in response to this event and a protective offshore breakwater was built to avoid future damages. For a comprehensive list of flooding events in the Maldives, the reader is referred to Wadey et al. (2017) , where the available information of several flooding events has been collected from a number of sources.

Despite the recurrent flooding episodes associated with swells, overall, in the Maldivian archipelago a complete and accurate assessment on the wind-wave climate, including extreme waves, is hindered by the lack of observations and regionalisation of model runs. Numerical wind-wave simulations are available with a global coverage, including both re-analyses (i.e., Saha et al., 2010 ) and projections (i.e., Hemer and Trenham, 2016 ; Morim et al., 2019 ), although with a coarse resolution that prevents their use for many practical purposes, such as accurate local assessments. This work intends to fill this gap by providing the necessary information on waves to perform coastal studies along the Maldivian shorelines. The objectives of the present study are three-fold: first, we fully characterise the wave climate around the Maldives on the basis of global, coarse resolution numerical wave dynamical simulations for present-day, and we further evaluate the projected changes under climate change scenarios (section 3). Secondly, we downscale the extreme wave climate through propagation of the main extreme waves from the dominant directions toward the coastlines with a much higher resolution (section 4). And finally, we illustrate how this information can be translated into a flood hazard assessment in a selected location that is exposed to the largest incoming swell waves in the archipelago. To do so, we propagate wave conditions from the nearshore to the coastline under different mean sea-level rise scenarios and quantify the flooding extent with and without land reclamation (section 5). Data, methods and numerical models are described in section 2, while all the results are discussed together in section 6.

2. Data and Methods

This section describes the global wave data that is used to characterise and downscale wave information to the nearshore in the Maldives, together with the numerical models and their implementation. Local wave modelling is used as the basis of flood hazard assessment for a case study. To do so, waves are combined with a set of mean sea-level changes using a scenario-independent approach. That is, waves are propagated toward the shoreline under prescribed mean sea-level increments of 0.25, 0.5, 0.75, and 1 m with respect to present-day averaged value. Note that these values are not necessarily interpreted as climate-induced mean sea-level rise; they can also be associated to tidal oscillations or to a combination of tides and mean sea-level rise.

2.1. Global Wind-Wave Datasets

We have used the CAWCR Global wind-wave data set that is freely distributed through the CSIRO data server ( Hemer et al., 2015 ). This set, generated with the WaveWatch III wave model (version 3.14, Tolman, 2009 ) in a common 1° × 1° resolution global grid, consists of a hindcast, historical runs (late twentieth century), and projections for the twenty-first century. The hindcast has been forced with surface wind fields from the NCEP CFSR ( Saha et al., 2010 ) and covers the period from 1979 to 2009 with a temporal resolution of 1 h (this simulation is referred to as CFSR hereinafter). The historical runs and projections were generated using the output fields of 8 different CMIP5 models (ACCESS1.0, BCC-CSM1.1, CNRM-CM5, GFDL-ESM2M, HadGEM2-ES, INMCM4, MIROC5, and MRI-CGCM3), covering three different time periods with a temporal resolution of 6 h: historical runs for 1980-2005; and projected waves for mid-(2026–2045) and late-(2081–2100) twenty-first century. The projections for mid- and late-twenty-first century were run under two different emission scenarios, RCP4.5 and RCP8.5, although we will use only the latter. A detailed description of the wave climate dataset can be found in Hemer et al. (2013) .

Global wave models are used to characterise the present-day and future projected changes of wave climate around the Maldivian archipelago, with emphasis on the extreme wave climate. Return levels of Hs for a set of prescribed return periods are calculated by fitting the top 1% waves to a Generalised Pareto Distribution. Given the coarse spatial resolution of the model configuration, we do not expect the small islands as the Maldives to be accurately represented by these global simulations. Given that the wave fields are modified by the presence of the islands (see for example Supplementary Video 1 from Amores and Marcos, 2019 ), the global fields must be downscaled in order to be usable for practical purposes. This process is described in the following.

2.2. Regional Wave Modelling

Global waves have been dynamically downscaled in the Maldives using the WaveWatchIII wave model (version 4.18, Tolman, 2014 ). The model was implemented on an unstructured mesh with 33160 nodes and 64456 elements over a domain ranging from 71.5 to 75.5° E in longitude and from −1.5° N to 8.5° N in latitude (black rectangle surrounding the Maldives in Figure 1 ). The spatial resolution of the unstructured mesh varied from 50 km along the boundaries of the domain down to 500 m in the channels between the atolls. Only the external coasts of the atoll islands were considered due to the lack of bathymetric information inside the atolls. The regional bathymetry used to build the model grid was the GEBCO bathymetry 2014 in a global 30 arc-second interval grid ( https://www.gebco.net/ ). The wave spectrum was defined by a directional resolution of 10° and 24 frequency bands ranging non-linearly from 0.0373 to 1.1 Hz. Dynamical downscaling was preferred instead of statistical approaches because there is no local information on waves that can be used to calibrate the model.

2.3. Local Wave Modelling

Nearshore downscaled waves have been propagated toward the coastline for a case study site. The selected location corresponds to Haa Alif atoll (HA) at Hoarafushi island, located at the north of the archipelago ( Figure 1 ). Hoarafushi has a maximum length of 2,500 m and a maximum width of 500 m ( Figure 1 ). This site has been chosen for two main reasons: firstly, at the start of this study a land reclamation project to build a new airport next to the island was foreseen. The development of the regional airport on the newly reclaimed island on the reef of HA Hoarafushi is part of the government's regional development and decentralisation plans, which puts extra focus on the northernmost atoll Ihavandhippolhu. We therefore aimed at evaluating the exposure of this new reclaimed land to incoming waves and how its presence can alter the wave propagation over the reef and the exposure of the current island. The process of land reclamation was started on April 16th, 2019 ( https://edition.mv/news/10159 ) and finished almost 5 months later, on September 5th, 2019 ( https://edition.mv/news/12266 ; see Supplementary Figure 1 , to see the construction process on June 15th, 2019). Secondly, information on the local bathymetry and land elevation is available and allows to simulate the wave propagation. A bathymetry around the island was generated by combining measurements on the reef flat performed by the Maldives Transport and Contracting Company, who was in charge of the design of the land reclamation project. We completed these data with reef slope measurements taken during a field trip on February 2018 (using a single beam echosounder). Our measurements included a total of 10 profiles across-slope separated around 200–500 m between them as well as several along-slope transects. The minimum depth measured in the across-slope profiles was around 3 m, that was the closest the boat could get to the reef crest, and the maximum depth recorded, that was fixed by the maximum range of the echosounder, was around 50 m. Unfortunately, there is no detailed information on the topography of the island. Instead, a constant land height of 1.5 m above present-day mean sea level has been used, according to visual inspections and in accordance with existing regulations. The coastline of the island has been represented with a constant slope, given that there are not hard structures in the oceanward side. Two topo-bathymetries have been implemented, with and without the presence of the airport. Finally, it is worth mentioning that HA Hoarafushi island is exposed to the highest incoming waves around the archipelago, as will be shown below.

The local wave propagation has used the SWASH model ( Zijlema et al., 2011 , code available at http://swash.sourceforge.net/ ) in a 2D regular grid of 6,220 m in the W-E direction and 7,320 m in the S-N direction with 10 m of spatial resolution (see the domain in Figure 8 ). This model is suitable for our purposes as it is capable of simulating wave setup and runup and predicting infragravity waves in the nearshore ( Rijnsdorp et al., 2012 ), a relevant process that contributes to the amount of flooding by raising temporary the sea level near the coast. The West and South boundaries were considered active introducing the wave forcing in the domain with Jonswap spectra with a wave dispersion of 20° and a peak enhancement parameter γ of 3.3. A different combination of wave dispersion and γ was tested (5° and 10°, respectively), resulting in essentially the same results in terms of flooding. A 150 m sponge layer was placed in the eastern boundary and 1,000 m sponge layer in the northern boundary, to avoid unrealistic wave forcing from the interior of the atoll given by spurious wave reflection from the those boundaries. The lack of in-situ measurements of wave propagation and transformation along the domain made it impossible to calibrate the Manning's friction coefficient. The values for coral reefs found in the literature vary from 0.01 to 0.2. For example, Zijlema (2012) used 0.01, Prager (1991) used 0.05, Kraines et al. (1998) used 0.1, and Cialone and Smith (2007) used spatially-varying Manning's coefficient values of 0.02, 0.19, and 0.2 depending on the region of their domain. The Manning's coefficient value was finally fixed to 0.019 following Suzuki et al. (2018) , who investigated the most suitable value for SWASH model applied to overtopping computation along a beach profile with defined defenses. In our case, there is not a complete beach profile, but the overtopping, which is the process of interest here, is occurring at the shoreline of a sandy beach.

With this configuration, the total simulated time for each combination of parameters was 70 min, with an initial integration time of 0.05 s and having outputs every 5 s. This is computationally intensive but still feasible for the range of experiments and for the two topographies (with and without the airport).

3. Characterisation of Wave Climate Around the Maldives

3.1. present-day wave climate.

The outputs of the CFSR wave hindcast at 24 grid points around the Maldives are used to describe the large-scale present-day wave climate in the archipelago ( Figure 2 ). Wave roses in Figure 2 identify, for each grid point, the direction of the dominant wave regimes with their corresponding significant wave heights ( H s ) and peak periods ( T p ). One prominent feature is that the largest significant wave heights are usually accompanied by peak periods longer than 10–12 s (and reaching up to 24 s), which suggests that these are remotely generated waves, i.e, swell waves. This is in agreement with the location of the Maldives in the Equatorial region, where winds are weak, and in a region exposed to swell waves from the Southern Ocean ( Wadey et al., 2017 ; Amores and Marcos, 2019 ) and is further examined below.

Figure 2 . Distribution of the ocean wave climate around the Maldives from the CFSR Hindcast. Each wind-rose-plot corresponds to one point of the central map. The radial distance of each single point in each wind-rose indicates the wave height (m) while the azimutal value indicates the direction that the waves are coming from in nautical convention. The colour of each point shows the peak period. The continuous black (grey) line indicates the quantile 50 (99) for each direction while the dashed black like shows the quantile 50 averaging all the directions. Shadowed areas in the wave roses indicate the most frequent incoming wave directions in a 1° bins (% referred to the radial axis).

Waves from the south-west (~205°) are the most common with H s reaching values larger than 4 m (note that the angles follow the maritime convention, as indicated by the labels in the wave rose of point #1). This finding is in line with Amores and Marcos (2019) that demonstrated that between 80 and 90% of the swell events impacting along the Maldivian coastlines are from SW and originated in a region located between south of Africa and east of South America. The second most frequent direction is the south-east (~145°). These waves reach maximum values of H s around 3 m, thus smaller than ~205° waves, and with peak periods between 10 and 12 s. In addition to these two dominant swell wave directions, two other cases much less frequent but with non-negligible H s are detected. In the north of the archipelago the largest waves with H s of up to 5 m are from the west direction (~275°, see wave-rose #17 in Figure 2 ). And finally, waves from 60° are also found in the points of the northeastern side of the archipelago (see, for example, wave-rose #10 in Figure 2 ) with peak periods smaller than 10 s and H s smaller than around 2.5 m.

The characteristics of the incoming large-scale waves are further analysed in greater detail for three grid points capturing the entire range of directions: point #17 (northwest), point #3 (south), and point #10 (northeast). Figure 3 examines the annual and seasonal distribution of incoming waves for every direction and their classification in terms of wind-seas and swells, according to the spectral partitioning provided by the global wave models. These histograms, representing the number of events per year, have been constructed with wave events separated at least 3 days to avoid over-representation of the dominant directions and with a minimum peak prominence H s of 0.2 m to remove noise from smaller waves. The three points are representative of the four incoming wave directions identified above and all register a similar number of waves during the hindcasted period (between 45 and 50 per year, as listed in the title of the panels in Figure 3 ). Their distribution in directions is, however, different, and depends on their position. The most frequent wave direction, around 205°, is evident in points #17 and #3 and is equally likely throughout the entire year (see panels d, e, g, h for comparison among seasons). A composite of the wave and wind fields corresponding to these events is mapped in Supplementary Figure 2 , demonstrating that these waves indeed correspond to remotely generated southwestern swells, in line with the findings in Amores and Marcos (2019) . Waves from the west direction, around 275°, are the second most frequent in point #17 with a marked seasonal character, being only detected between May and October (panel d) and classified as a mixed sea+swell. These waves are generated by the Indian monsoon and only affect the northernmost area of the archipelago. The corresponding composites are shown in Supplementary Figure 3 . The presence of waves generated by the Indian monsoon likely has an impact on the wave type distribution of the southwestern swell at point #17, since its percentage of sea+swell is larger between May and October; also, the wind fields of the composites corresponding to both types of waves are identical (see last rows in Supplementary Figures 2, 3 ).

Figure 3 . Histograms of wave direction (in nautical convention) registered at the three points selected as being representative (point #17 in the first column ( a,d,g ), #3 in the second ( b,e,h ), and #10 in the third) ( c,f,i ). The first row shows the annual histograms ( a,b,c ), May-October histograms are shown in the second row ( d,e,f ) and November-April histograms are in the last row ( g,h,i ). Each pie chart indicates the spectral separation by type of wave produced by WaveWatch III model [pure sea ( H s of swell = 0), pure swell ( H s of sea = 0), sea + swell dominated by sea ( H s of sea > H s of swell) and swell + sea dominated by swell ( H s of swell > H s of sea)] corresponding to each wave component identified (grey shadows).

The second peak in point #3, seven times less frequent that the southwestern swell and also observed in point #10, corresponds to the direction around 145°, with waves detected throughout the entire year. According to the wave and wind fields composites ( Supplementary Figure 4 ) these are waves generated in the Southern Ocean, in a region off the southeastern coast of Australia ( Amores and Marcos, 2019 ). Finally, the fourth incoming direction, around 55°, is clearly detected in point #10, with a strong seasonal character. These waves correspond to the northeast monsoon ( Wadey et al., 2017 ) and are only relevant between November and April, contrasting with the Indian monsoon (panel f and i).

Return levels of H s for every direction and for the three grid points are shown in Figure 4 and listed in Supplementary Table 1 . Noteworthy are the flat tails for the southeastern swells evident in points #10 and #3. Independence among wave events is ensured with the 3-day declustering. A Generalised Pareto Distribution (GPD) has been fitted to the top 1% of the largest H s ; in the case that this subset is too small as to reliably fit the distribution, the 30 largest values (1 event per year on average) were used. The largest return levels correspond to waves generated by the Indian monsoon in point #17 ( Figure 4D ). This direction has a H s of 4.75 m for a 10 year return period that is larger than all the return levels for the 500 year return periods for all cases (with the exception of the southeastern swell affecting point #3 that has 4.99 m as H s associated with 500 year return period). On the other side, the lowest return levels correspond to the northeast monsoon affecting point #10 with a H s equal to 2.74 m for a return period of 500 years, around 1 m lower from the closest return level (3.61 m for 500 year return period for the swell coming from southeast in point #3).

Figure 4 . Return levels associated with each return period (thick continuous lines) for the three representative points (point #17 in the first column (a,d) , #3 in the second (b,e) , and #10 in the third) (c,f) for the wave directions identified at each point (for example, panel a corresponds to the first grey shadow in Figure 3a ). The uncertainty bands correspond to ±σ (dashed lines) and the 5−95 % intervals (dotted lines) and have been computed using the delta method. The return period indicated in the top of the panels (10, 20, 50, 100, and 500 years) are the ones selected to perform the regional downscaling with WaveWatch III. Note that the y -axis are different for each panel and do not allow a direct comparison.

3.2. Wave Projections During the Twenty-First Century

The same three grid points analysed above are used as proxies to evaluate the projected changes in waves around the Maldives, using the output of historical simulations and projections during the twenty-first century. Figure 5 represents changes in the frequency of arrival of waves for each direction of propagation by the end of the twenty-first century under RCP8.5 with respect to present-day values for each point. The median of the 8 climate model projections is shown in red (blue) when the projected changes indicate an increase (decrease) in the number of wave events and the grey area represents the model spread. Global models project an increase (~3%) of the southwestern swells, consistent with the findings in Amores and Marcos (2019) , who showed a greater activity in swell generation in the region of formation of these waves later in this century. For the waves generated by the Indian monsoon, models show a smaller decrease in the number of waves. Other directions do not show robust projected changes, as the model spread is larger than the median change. The same applies to projected variations in median and extreme H s in all directions of propagation ( Supplementary Figure 8 ).

Figure 5 . Projected changes in wave direction by the CMIP5 models described in section 2.1 for each one of the representative points selected ( a point #17, b point #3, and c point #10). Black line represents the CFSR hindcast histogram (same as the first row in Figure 3 ); grey shadow indicates the spread of the CMIP5 models (RCP8.5 - Historical); red (blue) shadows show where the models agree to project a frequency increase (decrease) of a given direction.

Overall, projected changes in H s are smaller than the multi-model spread even under RCP8.5 climate scenario. Variations are expected to be even smaller under RCP4.5. In consequence, present-day significant wave height is considered to be largely representative of future wave climate for the purposes of this work and only CFSR wave fields will be downscaled and propagated toward the shorelines. It is worth noting that changes in the frequency of each wave direction ( Figure 5 ) can be relevant to the transport of sediments and could modify current erosion patterns.

4. Regional Wave Downscaling

Global wave information needs to be downscaled to become representative and usable in the nearshore; however, downscaling the full hourly 30-year CFSR hindcast is computationally too intensive. On the other hand, in terms of coastal impacts assessments and, in particular when coastal flooding is concerned, it is extreme values that are the most relevant metric. Therefore, our approach consists of dynamically downscaling the return levels for H s calculated for 6 different return periods (namely, 10, 20, 50, 100, 500, and 1000 years) and the four main wave directions that were previously identified. To do so, we have used the Wave-WatchIII model configuration described in section 2.2. The H s return level associated with a given wave direction is defined at a reference grid point and propagated along the corresponding boundary. In order to insert consistently the H s at the rest of the grid points in the same boundary, the linear relationships between simultaneous events (±24 h ), arriving from the same direction and reaching the reference point and the other boundary points were computed. This procedure is illustrated in Supplementary Figures 9–12 , where also the reference grid points at each boundary are marked. The linear relationships between the reference grid point and the others are used to scale H s at each active boundary point. The boundary points where no simultaneous events with the reference point were found or, alternatively, for which there is no correlation (we set the limit value of R 2 of the linear adjustment to 0.2), were assigned a linear slope of 0.01 in order to avoid introducing spurious waves. The peak period ( T p ) of the incoming waves associated with each return level for H s , have been determined using a linear relationship between all the ( H s , T p ) events extracted at each reference point for each of the four directions of the incoming waves ( Supplementary Figure 13 ).

The resulting downscaled wave fields consist of a set of four return level curves at every coastal grid point with a spatial resolution of ~500 m. This resolution permits to model wave propagation at the scale of the archipelago. Although it is not accurate enough to perform local assessments inside an atoll, it provides, instead, the necessary boundary condition for the forcing. The full data set is provided at the Zenodo repository under this doi: 10.5281/zenodo.3886273 . Figure 6 shows the results for the 100-year return level of the four directions over the entire domain, sorted by decreasing H s . Note that the spatial patterns of different return levels will be the same for each wave direction and only the magnitude changes. Due to the limited resolution of the GEBCO topobathymetry (~1 km ), an accurate representation of the islands and the inner part of the atolls is not feasible. Thus, the atolls have been considered as whole entities. This assumption implies that the side of the islands that faces toward the atoll's interior is not solved by our regional downscaling. Nevertheless, it is not relevant at this scale because this side of the islands is not directly impacted by waves. We consider that, given the limited depth on the atoll rims (roughly 1 m), this assumption is reasonable, especially because a more accurate assessment would require tide-current local modelling to capture lagoon/ocean interactions.

Figure 6 . Regional downscaling of the 100 year return period wave event performed with WaveWatch III model (see section 2.2 for the details) for each one of the wave components identified [ (a) Indian Monsoon, (b) Southwestern Swell, (c) Southeastern swell, and (d) Northeastern Mosoon]. Black arrow in each panel indicated the wave direction. Black stars indicate the position of Malé, the main city of the Maldives, and Hoarafushi, the island where the local modelling was done.

Figure 6 shows that the largest waves in the Maldives ( H s >5 m ) are generated by the Indian monsoon (panel a) in the northwestern part of the archipelago, with values of H s exceeding 2 m in the area northwards from 3°N (note that the same colour scale is used for the four maps). One remarkable feature is that these waves, although attenuated, reach the western side of the Kaafu atoll, the most populated atoll in the Maldives and where the capital city Malé is located. Because of the absence of shadow effects, the western coast of the Kaafu atoll, is the inner region of the Maldives exposed to waves with larger H s , reaching values between 2.5 and 3.0 m. The southwestern swell (panel b), the second direction with largest H s after the Indian monsoon, is the component that spreads larger H s to a broader scale. More precisely, it generates ocean waves with H s >3 m (even than 3.5 m) to all the western sides of the atolls comprising the Maldives. The third ocean wave direction in terms of H s is the southeastern swell (panel c), that affects all the eastern side of the Maldives with H s ranging from 2 to 3.5 m. Finally, the northeastern monsoon (panel d) is the ocean wave component with smaller H s (<2 m ). Its effects are concentrated in the central region of the eastern side of the archipelago, from 2 to 6.5°N. It does not strongly affect the northernmost part of the Maldives because this region is located under the shadow of the Indian continent to the monsoon winds ( Supplementary Figure 6 ).

Combining the results of the four wave directions shown in Figure 6 , we can identify the wave component with greater H s at each grid point along the coastlines ( Figure 7a ), the value of this greater H s ( Figure 7b ), as well as how many different directions each coastal point is exposed to Figure 7c ; H s ≥1.5 m . In relative numbers, 33% of the coastlines are exposed to the large waves from the Indian monsoon, in 25% of them the highest waves arrive from the southwestern swell, in 28% from southeastern swell, and only 14% from the northeastern monsoon. As in the case of the Kaafu atoll mentioned above, a similar effect is found in the eastern part of the Faafu and Dhaalu atolls, also located in the interior of the Maldives. Here the dominant wave component reaching the eastern coast of these atolls is the southeastern swell that penetrates in the middle of the Maldives between Thaa Atoll and Meemu Atoll.

Figure 7 . Products derived by combining the regional downscaling for the 100 year return period of the 4 wave components in Figure 6 along the Maldivian coastlines. (a) shows the wave component causing the largest H s at each coastal point; (b) the maximum H s at the coast; and (c) , the number of wave directions with H s larger than 1.5 m that hit each coastal location for the 100 year return period.

In terms of maximum H s ( Figure 7b ), around 15% of the coastal points, most of them located in the interior of the archipelago, are affected by waves with 100-year return periods smaller than 1 m. The most common values are between 1 and 2 m, affecting 35% of the coastal locations. In 22% of the coasts, the 100-year return levels of H s vary between 2 and 3 m and in 17% H s between 3 and 4 m. The largest values, over 4 m, affect around 11% of the coastal points which are found, as expected, in regions where the Indian Monsoon dominates ( Figure 7b ).

Another metric for the exposure of the coasts to incoming waves is the number of swell directions reaching every coastal point. This is illustrated in Figure 7c , where we have quantified how many wave directions, from the 4 represented in Figure 6 , reach each coastal point with H s ≥1.5 m for the 100 year return period. The choice of the H s threshold and the return period selected is arbitrary and used only for illustration purposes; it is not determinant for the resulting map. We conclude that, in 32% of the coastal points, the 100-year return level of H s is always smaller than 1.5 m (grey points in Figure 7c ), with these areas located mainly in the interior of the archipelago. In 29% of the coastal points waves arrive from a single direction (blue points) and in 38% from two directions (yellow points), with the latter case mainly affecting the eastern and western side of the Maldives. In only 1% of the coastal grid points waves arrive from 3 directions (red points), but these are concentrated in the easternmost side of the Vaavu atoll.

5. Local Wave Modelling and Flood Hazard in Hoarafushi Island

The outputs of the regional wave downscaling developed in the previous section are used here in a local flood hazard assessment, illustrating its direct applicability. To do so, downscaled nearshore wave information in a coastal grid point next to Hoarafushi island is propagated toward the shoreline and used to assess coastal flooding under different mean sea-level rise scenarios. The are two reasons that make this location particularly interesting for local wave modelling: first, it is affected by the two largest wave components in the archipelago, i.e., the Indian Monsoon and the southwestern swell; and second, a new island was reclaimed to host a regional airport, which raises questions of present and future climate hazards (see section 2.3). The projected airport, that will have a length of around 1.5 km and a width of 300 m in its wider section, will be located in the reef of the island that faces toward the outer side of the atoll. This means that the shoreline of the airport will be substantially closer to the reef edge than the original island (150–200 m instead of 600 m), reducing the amount of wave energy that can be absorbed by the reef. This local-case study does not pretend to give any recommendation to stakeholders on the airport island height for this specific site. To do so, detailed local information, such as a high-resolution topo-bathymetry or ocean waves in-situ data to validate the model outputs would be required. This example illustrates the applicability of the regional wave downscaling developed here to a local study if precise local information was available.

Wave propagation with SWASH was carried out in the domains in Figure 8 . In total, 60 different runs were completed by combining 3 different return periods of H s (10, 50 and 100 years), two wave directions (Indian Monsoon and the southwestern swell), and 5 different mean sea levels (0, +0.25, +0.50, +0.75, and +1 m ) for the island configuration with and without airport. We have followed a scenario-independent approach for mean sea-level rise, with 0 m corresponding to present-day mean sea level. Mean sea-level changes with respect to the current situation may be interpreted in terms of projected mean sea-level rise (e.g., +0.50 m is the median projected mean sea-level rise in 2068 under RCP8.5 and 2088 under RCP2.6, according to Kopp et al., 2014 ) or as a combination of mean sea-level rise and high tides (e.g., +0.50 m is the mean rise in 2041 under RCP8.5 plus +0.25 m of tidal amplitude). The mean sea-level changes tested may also include, besides projected mean sea-level rise and tides, other physical processes that can cause mean sea-level variations from seasonal to decadal time scales. We recall here that tides in the Maldives reach a maximum range of around 1 m (0.7 m median range, Wadey et al., 2017 ). Note that precise geodetic references relating altitudes and tidal levels are lacking in the Maldives, so these values should be considered as an order of magnitude only. Four examples of selected simulations can be found in Supplementary Videos 1, 2 .

Figure 8 . Example of local downscaling simulations with SWASH model (see section 2.3 for details) for the 10 year return period southwestern swell event with 0.5 m of sea level rise (this increase in sea level could mean permanent sea level or high tide with present sea level) for the case without the airport (a) and with the new airport (b) . Grey (purple) stripe indicates the coastal region where the box plots from Figure 9 ( Supplementary Figure 15 ) are computed.

It has not been possible to validate the model outputs for the present-day situation due to the lack of observations. We are providing, nevertheless, a qualitative validation by comparing the velocity field obtained with the configuration that includes the airport to a satellite photography in which the airport is under construction ( Supplementary Figure 1 ). There is a consistency between higher current velocities in the model and the imprint of sediment transport from the new-built airport that are likely driven away by the currents.

The outputs of the first set of 30 model runs, that correspond to the spatial configuration without the airport ( Figure 8a ), are used to evaluate the exposure of the island in terms of the amount of flooding under different forcing conditions. The outputs along a 100-m wide coastal strip covering the western coast of the island (plotted as grey area in Figure 8a ) have been gathered together. To do so, the strip is divided in 25-m long sections resulting in 25 × 100 m boxes. Simulated water level time series were extracted for each box and used to compute median and maxima water levels for each model run in each of them. Figure 9 represents the boxplots along the entire coastal strip of these median (left panel) and maxima (right panel) values under all mean sea levels and return levels considered. The horizontal black thick line in both panels marks the height of the island and the two incoming directions are separated by vertical shadowed areas for comparison. Median values of total water level, that correspond to the superposition of the mean sea level and wave setup, do not reach the threshold of land elevation, indicating that there is no overflow at any point along the coastline under all the forcing conditions considered. The results also point at the southwestern swells as the potentially most hazardous waves, as these systematically induce higher water levels than the Indian monsoon waves (shadowed areas against blanked areas). The reason lies in the longer T p associated with the southwestern waves (~20 s ) in front of the monsoon waves ( ~12 s ). As expected, the larger wave setup for a given return period is obtained for the lowest mean sea level of 0 m : wave setup reaches almost 0.4 m under present-day mean sea level conditions and reduces to 0.3 m with an increase of 1 m . This is because in shallower waters the effects of wave shoaling and breaking leading to wave setup are larger. It is worth noting here that while an increased water level leads to a decreased setup, deeper water allows for larger H s on the reef flat and an increased run-up potential which could be relevant in terms of impact to infrastructures and erosion. On the other hand, maximum values along the coastal strip have been used to measure whether there has been overtopping generated by the incoming waves. Overtopping occurs whenever these values exceed the island elevation, with their magnitude indicating the severity of the flooding. The boxplots for the maximum values (right panel in Figure 9 ) point to the occurrence of overtopping under several forcing configurations. For example, 100-year return level waves from southwestern swell and +0.5 m mean sea level increase. Note that this may correspond to a 1 in 100-year events reaching the coast during the spring tides and under present-day mean sea level conditions. It also occurs for moderate extreme waves with a return period of 10-years in combination with +1 m of mean sea level (this case is also provided in the Supplementary Video 1 ) and for all the return periods for the southwestern swell with +0.75 m of mean sea level rise.

Figure 9 . Box plots along Hoarafushi coast without airport computed with time series of simulated water levels: (a) median values; (b) Maximum values. Box plot colours indicate the sea level of the simulation (dark blue 0 m; light blue 0.25 m; green 0.5 m; orange 0.75 m; dark red 1 m) and are referenced from the dashed line with the same colour. Box plots on grey (white) background are for the simulations for the southwestern swell (Indian Monsoon). The thicker line of the box plots shows the median values; the lower (upper) limit of the boxes indicates the 25th (75th) quantile; and the lower and upper whiskers indicate the minimum and maximum values. The horizontal thick black line indicates the island height.

With the construction of the airport connected to Hoarafushi ( Figure 8b ), the median and maximum water level values computed along the coast (grey area in Figure 8b ) slightly increased for all combinations of mean sea level, extreme waves and wave directions (see the equivalent figure to Figure 9 in Supplementary Figure 14 ). On average, the median values of water level along the coast increase around 0.05 m solely due to the presence of the airport, that partially blocks the channel between Hoarafushi and the island located southwards, leading to higher wave setup. The new reclaimed land is also exposed to incoming waves, and this exposure has been measured in a similar manner as for Hoarafushi, i.e., along a coastal strip on its western coast (blue area in Figure 8b ). We remark that the airport has been built 150-200 m away from the reef edge, reducing to a large extent the protection of the wave damping induced by the reef flat. Consequently, both median and maxima water level values are significantly higher than in Hoarafushi island ( Supplementary Figure 15 ). For example, with +1 m of increase in mean sea level, even moderate extreme waves would cause overtopping (e.g., 10-year return levels or less under high tide), and under current conditions a 50-year return level southwestern swell would partially flood the airport.

The flood hazard of the new reclaimed land is summarised in Figure 10 , using the set of 30 simulation runs with the airport. The flood hazard has been defined following the French standards, that define four different flooding hazard levels (low, moderate, high, and very high) that arise as combinations of inundation level and the water speed over land (see Supplementary Figure 16 ). The artificial island built for the airport is completely flooded with a high level of hazard for most part of the island for both wave directions and all return periods with an increase in mean sea level of ≥0.75 m (with the only exception of the Indian monsoon 10-year return period). It is foreseen that the reclaimed land suffers from partial flooding under a southwestern swell extreme of 50-year return period with current conditions of mean sea level. It is worth mentioning that, given the lack of topographic data for the new airport island, flooding hazard is possibly biased high. We simulated the island as being completely flat and without any coastal defenses. This is unlikely to be the case for a critical infrastructure. However, the actual defense height remains unknown, which is why we assume compliance to land reclamation regulations i.e., 1.5 m land elevation. Coastal defenses would only delay the impact of coastal flooding, but would not avoid it.

Figure 10 . Level of hazard on the new airport for all the SWASH simulations. The colourscale indicates the level of hazard defined by a combination of water height on the airport and water velocity (see Supplementary Figure 16 ). Different sea levels are represented at each row while the columns indicate return periods of H s (10, 50, and 100 years) as defined in the text for the regional wave climate. For each combination of sea level and return period, the result for the Indian Monsoon and Southwestern swell are shown at left and right, respectively.

6. Summary and Discussion

6.1. global to local coastal modelling.

Mean sea-level rise, despite having a global origin, has severe local coastal impacts, as it raises the baseline level on top of which extreme events reach the coastlines. Yet, projections of changes in mean sea-level as well as assessments of marine extremes are often provided on a large-scale basis (e.g., Vousdoukas et al., 2017 ), while understanding the causes of coastal flooding and anticipating the impacts require quantitative information at the local scale. This can be feasible to implement in regions where monitoring networks, forecasting and operational systems and development programs for sustainable coastlines are well established and mature (for example, the Flood and Coastal Erosion Risk Management Programme in the UK, or the Delta Programme in the Netherlands). In many cases, however, even local assessments rely on coarse resolution, large-scale global climate information.

In this work we have focused on the Maldivian archipelago, a region where recurrent flooding episodes occur driven by remotely generated waves. These events are, furthermore, projected to become more frequent as mean sea level rises due to the low elevation of the islands. Despite their exposure to waves, to our knowledge, the only source of wave climate information in the region so far are the outputs of global wave reanalysis with a spatial resolution of the order of a degree. Our work illustrates how these global wave fields from coarse resolution climate models can be translated into usable information for regional and local studies and how it can be combined with regionalised projections of mean sea-level rise and local topo-bathymetries.

The first step consisted of a detailed analysis and characterisation of the global wave climate around the Maldives using the closest grid points from the CFSR wave reanalysis (section 2.1). This is a prior mandatory step before the design of the regionalisation. We identified four dominant incoming wave directions from remotely generated waves: the two most common, that originate in the Southern Ocean ( Amores and Marcos, 2019 ), and swells generated by the Indian and Northwestern monsoons. In a second step, for each direction, extreme waves have been characterised in terms of H s and T p and a set of five return levels have been dynamically-downscaled using the spectral model WWIII (section 2.2). We have focused on extreme waves only because these are the most relevant for risk analyses; furthermore, the alternative of dynamically-downscaling a 35-year long reanalysis is unfeasible due to computational constraints (this worsens if historical runs and projections are considered). The regionalisation has resulted in a major product of the present work: a valuable data set of extreme waves along the Maldivian coasts with spatial resolutions down to 500 m in the points nearest to the coast. The data set is published at doi: 10.5281/zenodo.3886273 . The output of our regionalisation provides quantitative information on extreme waves, in the form of return level curves, at the regional scale in the Maldives and for the first time. This dataset is useful for coastal engineering studies, for feeding local coastal models of flooding hazards and for planning land reclamation and other regional developments. It also serves to compute the inundation potential at every location and for every incoming swell direction, that depends on wave energy, H s 2 · T p , in line with the “response approach” discussed in Sanuy et al. (2020) . Overall, it is expected to become a compelling source of scientific information that can be embedded in coastal climate services ( Le Cozannet et al., 2017 ; Kopp et al., 2019 ). The users should, nevertheless, ensure that the inherent uncertainties in the method and data are considered. This means that regional waves are representative of ocean swells in the vicinity of the atolls and that, for practical purposes, a detailed topobathymetry is needed is these regional outputs are to be used as boundary forcings. Also, the four main swell directions arriving to the archipelago are considered separately, since the generation mechanisms are independent; thus, every coastal location may be exposed to a different number of incoming wave directions, and all of them should be explored in a local case study, as illustrated in section 5 above.

There is a number of limitations in our regionalised wave fields. The bathymetry used in the regional wave model (GEBCO, see section 2.2) has a spatial resolution of ~ 1 km, which is not enough to resolve the features inside the atolls. We have therefore included every atoll as a single entity in the model domain, neglecting the wave propagation in the inner region and the exchanges between the lagoon of the atoll and the ocean. We consider, nevertheless, that this assumption is reasonable because our results provide evidence that shadow effects of the atolls to incoming waves are realistically simulated from all directions. That implies that we account for the waves that reach the external coast of the atolls everywhere in the Maldives. This limitation can be overcome in areas where mesoscale (~ 100 m resolution) bathymetric data sets exist, in which case the interactions with the inner lagoon can also be accounted for. Another caveat of the regional product is that only selected return periods of H s are provided, instead of an entire high-frequency time series at every coastal grid point. While the quantification of return levels is central to risk assessments, no information on averaged wave fields (useful for erosion studies, for example) is provided. Finally, it is worth pointing out that the regional product has not been validated against observations due to the lack of data.

6.2. Application for Coastal Flood Hazard

We have conducted a local flood hazard modelling experiment that demonstrates the applicability of the regionalised wave fields. Our case study is in the North of the archipelago, exposed to the largest incoming waves, and includes a land reclamation project. We have used the regionalised wave information to feed the wave propagation model SWASH around Hoarafushi island, where local bathymetry has been measured. We have estimated the flooding hazard under present-day conditions and also under projected future scenarios. Our analysis of the global wave climate revealed that projected changes in the large-scale wave characteristics during the twenty-first century are small in comparison to the multi-model spread even under the RCP8.5 scenario. Therefore, we rely on the downscaled regional wave reanalysis and assume that future changes in marine hazards will be driven only by mean sea-level rise. The local model does take into account the modification of the wave propagation due to higher mean sea levels, though. The set of the model experiments included the island configuration with and without the airport in order to determine how the presence of the new reclaimed land alters the flood hazard, the wave propagation and the associated currents.

Our results identified the southwestern swells as the potentially most hazardous waves in Hoarafushi, with 100-year return levels of H s up to 4 m and associated T p of ~20 s. This is, in addition, the most common wave direction that reaches this part of the archipelago, although not the one with largest H s (that are associated with the Indian monsoon). Our findings indicate that a moderate incoming southwestern swell corresponding to a return period of only 10 years will cause overtopping in Hoarafushi island if it reaches the shoreline under a mean sea level 0.75 m higher than its present-day value ( Figure 9 ). The presence of the reclaimed land slightly increases these impacts ( Supplementary Figure 14 ). The flood hazard is much stronger in the reclaimed land, that will experience overtopping episodes with sea levels only 0.25 m above present-day mean value ( Supplementary Figure 15 ). The reason is its location close to the reef that reduces the wave damping over the reef flat. We recall here that we have adopted a scenario-independent approach for mean sea level increases; this may be justified given that the range of mean sea level changes that we are considering (below 1 m) will be reached even under strong mitigation, as the maximum value lies within the committed global mean sea-level rise of past GHGs emissions ( Nauels et al., 2019 ). Thus, it is not about whether these higher mean sea levels will be reached, but when it will occur. Impact studies based on scenario-independent approaches in combination with ongoing monitoring of regional mean sea-level rise can facilitate the design of adaptive solutions to climate-induced hazards.

In addition, this approach also allows to evaluate the wave-induced flood hazard under particular tidal conditions. In the example above, mean sea level 0.75 m higher than present-day values can be interpreted as a combination of climate-induced mean sea-level rise and tidal oscillations. For instance, 0.75 m can be reached with 0.5 m of climate-induced mean sea level that, according to Kopp et al. (2014) , corresponds to the median projected value in 2068 under the RCP8.5 scenario, plus 0.25 m of tidal amplitude. In consequence, according to our estimates, the recently developed (in 2019) regional airport will be flooded under present-day mean sea-level conditions and 0.25 m of tidal amplitude if a moderate extreme swell event (10-year return period) reaches the area, that is, within the present decade. Note that we are not computing the likelihood of co-occurrence of extreme swells and high tides. The reasons for that are, firstly, that these two processes are uncorrelated (astronomical tides and remotely-generated swell events have independent driving mechanisms) which means that their joint probability could be computed as the product of their marginal probability distributions ( Pugh and Woodworth, 2014 ). However, this would require a complete set of time series of the two processes at every grid point. Although there are methods to generate a set of full synthetic time series from their statistical characterisation (e.g., Solari and Losada, 2011 ), this is a different type of product that is beyond the scope of the present work. Secondly, our approach is more flexible since it does not constrain the interpretation of the increments in mean sea level (either climate-induced sea level rise or tides or both), hence, allowing final users to tailor our approach to their needs, based on their respective risk-taking propensity.

The modification of the island configuration with the presence of the reclaimed land significantly modifies the patterns of the currents ( Supplementary Figure 1 ). Such changes are determinant for coastal erosion, as they control the sediment transport along the coastlines. Coastal erosion is considered a central problem in the Maldives, especially in densely populated islands ( Zahir et al., 2016 ; Duvat and Magnan, 2019 ). Erosion can be prevented or enhanced by many factors, including land reclamation, dredging and building coastal defenses. Here we demonstrate that our regional wave fields are a valuable tool also for anticipating possible erosion and changing spatial patterns in particular case studies.

The major limitation of our local coastal modelling exercise is the lack of a detailed topography of Hoarafushi and its nearby reclaimed airport. While we have measured bathymetric profiles during a field trip, the information on the topography is limited to the averaged elevation of the island. Likewise, the elevation of the reclaimed land (which was not yet built when the field trip took place) has been defined according to the national regulations. In consequence, we have not included coastal defenses and we have instead considered that both the island and the new reclaimed land are flat. This implies that our estimates of overtopping and flooding could be biased high; however, the presence of coastal defenses would not completely avoid the flood hazard, they would simple delay the impacts of mean sea-level rise.

Another point worthy of discussion is the assumption of static bathymetry and null reef response to changing climatic conditions. It is clear that reefs can change over time. For example, they can accrete following sea level rise ( Woodroffe and Murray-Wallace, 2012 ), they can degrade due to human activities (the construction of the airport is a good example) or they can die as a consequence of warmer temperatures ( Bruno and Selig, 2007 ) (indeed, warm reefs are projected to significantly decline even with global warming only 1.5°C above pre-industrial levels ( Bindoff et al., 2019 ) and to be virtually extinct with 2°C of warming ( Hoegh-Guldberg et al., 2018 ). In any of these cases, changes in the reef would imply changes in the wave propagation and level of protection of the island ( Sheppard et al., 2005 ). We disregard these potential changes in our local flood hazard modelling experiment because we analyse an artificially reclaimed island. Here, human activities generally have severe negative effects on the reef ( Duvat, 2020 ) and the island is protected with hard measures. This is also to urban atoll islands, as Hoarafushi, that are continuously adapting to increased hazard potential by building coastal infrastructures or artificially raising the land ( Duvat and Magnan, 2019 ; Esteban et al., 2019 ; Hinkel et al., 2019 ; Brown et al., 2020 ). This reduces the ability of the island to naturally increase its elevation by sediment deposition during overtopping events ( Kench and Beetham, 2019 ). Hence, we argue that in this case human interventions are probably more important for wave propagation than changes in the reef ( Duvat and Magnan, 2019 ). Contrastingly, in a natural island, assuming a static bathymetry and null reef response, would bias the results of model overtopping ( Beetham et al., 2017 ; Beetham and Kench, 2018 ). Nevertheless, the regional downscaling that we provide serves as a boundary condition for subsequent studies of wave-induced flooding under future conditions, which then have to account for these uncertainties of future reef responses.

7. Concluding Remarks

Our study provides the framework to fill the gap between global information of marine climate drivers, including mean sea level and extremes, and local coastal flood hazard modelling. In particular, we demonstrate the feasibility of using large-scale data sets (regionalised sea-level projections and global wind-waves simulations) to inform regional planning and local decision-making. Our work focused in the Maldives, but our technique can be applied to any coastal region, being most relevant where regional and local climate information is not available. Together with the outputs, we have discussed a number of uncertainties in regional as well as local coastal modelling that are inherent to the methodology. Some of the limitations, though, stem, to a large extent, from the lack of coastal observations (i.e., local topo-bathymetries). Our study thus advocates for improved monitoring systems and data collection to reduce uncertainties and better inform final users.

We have generated a valuable regional wave data set that fulfils the purposes of characterisation of the wave climate in a sparsely observed area. This dataset, in combination with detailed local information (e.g., high-resolution topo-bathymetries), serves as a milestone for informing adaptation policy and Maldivian decision-makers facing the challenge of adapting to rising sea-levels.

Data Availability Statement

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below: https://zenodo.org/record/3886273#.YCFTAOhKhPY .

Author Contributions

AA, MM, GL, and JH conceived the work. AA, MM, RP, and SL designed the numerical experiments. AA, MM, and JR analysed the return periods. AS and ZK retrieved the topobathimetric data. All authors contributed to the outline and writing of the manuscript.

This study was supported by the FEDER/Ministerio de Ciencia, Innovación y Universidades Agencia Estatal de Investigación through the MOCCA project (grant no. RTI2018-093941-B-C31) and by the INSeaPTION Project that is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by Ministerio de Economía, Industria y Competitividad Agencia Estatal de Investigación (ES) (grant no. PCIN-2017-038), BMBF (DE), NOW (NL), and ANR (FR) with co-funding by the European Union (Grant 690462). This research has been also supported by the ANR project Storisk supported by the French Research Agency. AA was funded by the Conselleria d'Educació, Universitat i Recerca del Govern Balear through the Direcció General de Política Universitària i Recerca and by the Fondo Social Europeo for the period 2014–2020 (grant no. PD/011/2019). MM was supported by the Ministerio de Ciencia e Innovación and la Agencia Estatal de Investigación through grant no. IED2019-000985-I.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We are grateful to Dr. Aurélie Maspataud for her support with bathymetric data and Dr. Fernando Méndez for advice on numerical wave modelling. We thank the Ministry of Environment, the Environmental Protection Agency, the Maldives Transport and Contracting Company and Water Solutions for their support during the field trip and data collection. AA is grateful to M. A. Blázquez for his support and comments during the preparation of the manuscript.

Supplementary Material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fmars.2021.665672/full#supplementary-material

Amores, A., and Marcos, M. (2019). Ocean swells along the global coastlines and their climate projections for the 21st century. J. Clim. 33, 185–199. doi: 10.1175/JCLI-D-19-0216.1

CrossRef Full Text | Google Scholar

Beetham, E., and Kench, P. S. (2018). Predicting wave overtopping thresholds on coral reef-island shorelines with future sea-level rise. Nat. Commun. 9:3997. doi: 10.1038/s41467-018-06550-1

PubMed Abstract | CrossRef Full Text | Google Scholar

Beetham, E., Kench, P. S., and Popinet, S. (2017). Future reef growth can mitigate physical impacts of sea-level rise on atoll islands. Earths Fut. 5, 1002–1014. doi: 10.1002/2017EF000589

Bindoff, N. L., Cheung, W. W., Kairo, J. G., Arístegui, J., Guinder, V. A., Hallberg, R., et al. (2019). “Changing ocean, marine ecosystems, and dependent communities,” in IPCC Special Report on the Ocean and Cryosphere in a Changing Climate , eds H. -O. Pörtner, D. C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N. M. Weyer, 477–587, in press.

Google Scholar

Brown, S., Wadey, M. P., Nicholls, R. J., Shareef, A., Khaleel, Z., Hinkel, J., et al. (2020). Land raising as a solution to sea-level rise: an analysis of coastal flooding on an artificial island in the maldives. J. Flood Risk Manag. 13:e12567. doi: 10.1111/jfr3.12567

Bruno, J. F., and Selig, E. R. (2007). Regional decline of coral cover in the indo-pacific: timing, extent, and subregional comparisons. PLOS ONE 2:e711. doi: 10.1371/journal.pone.0000711

Cialone, M. A., and Smith, J. M. (2007). “Wave transformation modeling with bottom friction applied to southeast oahu reefs,” in 10th International Workshop on Wave Hindcasting and Forecasting & Coastal Hazard Assessment , (Citeseer), 1–12.

Duvat, V. K. (2020). Human-driven atoll island expansion in the maldives. Anthropocene 32:100265. doi: 10.1016/j.ancene.2020.100265

Duvat, V. K. E., and Magnan, A. K. (2019). Rapid human-driven undermining of atoll island capacity to adjust to ocean climate-related pressures. Sci. Rep. 9:15129. doi: 10.1038/s41598-019-54659-0

Esteban, M., Jamero, M. L., Nurse, L., Yamamoto, L., Takagi, H., Thao, N. D., et al. (2019). Adaptation to sea level rise on low coral islands: lessons from recent events. Ocean Coas. Manag. 168, 35–40. doi: 10.1016/j.ocecoaman.2018.10.031

Gussmann, G., and Hinkel, J. (2021). A framework for assessing the potential effectiveness of adaptation policies: coastal risks and sea-level rise in the maldives. Environ. Sci. Policy 115, 35–42. doi: 10.1016/j.envsci.2020.09.028

Harangozo, S. A. (2013). Flooding in the Maldives and Its Implications for The Global Sea Level Rise Debate (First Published: 01 January 1992) , (American Geophysical Union (AGU)), 95–99.

Hemer, M., Trenham, C., Durrant, T., and Greenslade, D. (2015). Cawcr global wind-wave 21st century climate projections (v2). CSIRO Service Collect . doi: 10.4225/08/55C991CC3F0E8

Hemer, M. A., Katzfey, J., and Trenham, C. E. (2013). Global dynamical projections of surface ocean wave climate for a future high greenhouse gas emission scenario. Ocean Model. 70, 221–245. doi: 10.1016/j.ocemod.2012.09.008

Hemer, M. A., and Trenham, C. E. (2016). Evaluation of a cmip5 derived dynamical global wind wave climate model ensemble. Ocean Model. 103, 190–203. doi: 10.1016/j.ocemod.2015.10.009

Hinkel, J., Church, J. A., Gregory, J. M., Lambert, E., Le Cozannet, G., Lowe, J., et al. (2019). Meeting user needs for sea level rise information: a decision analysis perspective. Earths Fut. 7, 320–337. doi: 10.1029/2018EF001071

Hinkel, J., Lincke, D., Vafeidis, A. T., Perrette, M., Nicholls, R. J., Tol, R. S. J., et al. (2014). Coastal flood damage and adaptation costs under 21st century sea-level rise. Proc. Natl. Acad. Sci. U.S.A. 111, 3292–3297. doi: 10.1073/pnas.1222469111

Hoegh-Guldberg, O., Jacob, D., Bindi, M., Brown, S., Camilloni, I., Diedhiou, A., et al. (2018). Impacts of 1.5°c Global Warming on Natural and Human Systems . Global warming of 1.5°C. An IPCC Special Report.

Hoeke, R. K., McInnes, K. L., Kruger, J. C., McNaught, R. J., Hunter, J. R., and Smithers, S. G. (2013). Widespread inundation of pacific islands triggered by distant-source wind-waves. Glob. Planet. Change 108, 128–138. doi: 10.1016/j.gloplacha.2013.06.006

Kench, P., and Beetham, E. P. (2019). Evidence of vertical building of reef islands through overwash and implications for island futures. Coastal Sediments 916–929. doi: 10.1142/9789811204487_0080

Kopp, R. E., Gilmore, E. A., Little, C. M., Lorenzo-Trueba, J., Ramenzoni, V. C., and Sweet, W. V. (2019). Usable science for managing the risks of sea-level rise. Earths Fut. 7, 1235–1269. doi: 10.1029/2018EF001145

Kopp, R. E., Horton, R. M., Little, C. M., Mitrovica, J. X., Oppenheimer, M., Rasmussen, D. J., et al. (2014). Probabilistic 21st and 22nd century sea-level projections at a global network of tide-gauge sites. Earths Fut. 2, 383–406. doi: 10.1002/2014EF000239

Kraines, S., Yanagi, T., Isobe, M., and Komiyama, H. (1998). Wind-wave driven circulation on the coral reef at bora bay, miyako island. Coral Reefs 17, 133–143. doi: 10.1007/s003380050107

Le Cozannet, G., Nicholls, R., Hinkel, J., Sweet, W., McInnes, K., Van de Wal, R., et al. (2017). Sea level change and coastal climate services: The way forward. J. Mar. Sci. Eng. 5, 49. doi: 10.3390/jmse5040049

Lecacheux, S., Pedreros, R., Le Cozannet, G., Thiébot, J., De La Torre, Y., and Bulteau, T. (2012). A method to characterize the different extreme waves for islands exposed to various wave regimes: a case study devoted to reunion island. Natural Hazards Earth Syst. Sci. 12, 2425–2437. doi: 10.5194/nhess-12-2425-2012

Maniku, H. A. (1990). Changes in the Topography of the Maldives . Forum of Writers on Environment (Maldives).

Marcos, M., and Woodworth, P. L. (2017). Spatiotemporal changes in extreme sea levels along the coasts of the north atlantic and the gulf of mexico. J. Geophys. Res. 122, 7031–7048. doi: 10.1002/2017JC013065

MEE. (2017). State of the Environment 2016. Ministry of Environment and Energy . Available online at: https://www.environment.gov.mv/v2/wp-content/files/publications/20170202-pub-soe-2016.pdf

Merkens, J.-L., Lincke, D., Hinkel, J., Brown, S., and Vafeidis, A. T. (2018). Regionalisation of population growth projections in coastal exposure analysis. Clim. Change 151, 413–426. doi: 10.1007/s10584-018-2334-8

Morim, J. L. M., Wang, H. X., Cartwright, N., Trenham, C., Semedo, A., Young, I., et al. (2019). Robustness and uncertainties in global multivariate wind-wave climate projections. Nat. Clim. Change 9, 711–718. doi: 10.1038/s41558-019-0542-5

Nauels, A., Gütschow, J., Mengel, M., Meinshausen, M., Clark, P. U., and Schleussner, C.-F. (2019). Attributing long-term sea-level rise to paris agreement emission pledges. Proc. Natl. Acad. Sci. U.S.A. 116, 23487–23492. doi: 10.1073/pnas.1907461116

NBS (2017). “Statistical yearbook of maldives 2016,” in National Bureau of Statistics Ministry of Finance and Treasury, Republic of Maldives (Malé).

NBS (2019). “Maldives population projections 2014-2054, assumption and results analysis,” in National Bureau of Statistics Ministry of Finance and Treasury, Republic of Maldives (Malé)

Nicholls, R. J., Hanson, S. E., Lowe, J. A., Warrick, R. A., Lu, X., and Long, A. J. (2014). Sea-level scenarios for evaluating coastal impacts. WIRES Clim. Change 5, 129–150. doi: 10.1002/wcc.253

Nurse, L., McLean, R., Agard, J., Bibruglio, L., Duvat, V., Pelesikoti, N., et al. (2014). “Small islands (chapter 29),” in Climate Change 2014 : Impacts, Adaptation, and Vulnerability. Part B : Regional Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change , eds V. R. Barros, C. B. Field, D. J. Dokken, M. D. Mastrandrea, K. J. Mach, T. E. Bilir, M. Chatterjee, K. L. Ebi, Y. O. Estrada, R. C. Genova, B. Girma, E. S. Kissel, A. N. Levy, S. MacCracken, P. R. Mastrandrea, and L. L.White (Cambridge, UK; New York, NY: Cambridge University Press), 1613–1654. Available online at: https://www.ipcc.ch/site/assets/uploads/2018/02/WGIIAR5-Chap29_FINAL.pdf

Oppenheimer, M., Glavovic, B., Hinkel, J., van de Wal, R., Magnan, A., Abd-Elgawad, A., et al. (2019). “Sea level rise and implications for low-lying islands, coasts and communities,” in IPCC Special Report on the Ocean and Cryosphere in a Changing Climate , eds H.-O. Pörtner, D. C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N. M. Weyer. Available online at: https://www.ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities/

Prager, E. J. (1991). Numerical simulation of circulation in a caribbean-type backreef lagoon. Coral Reefs 10, 177–182. doi: 10.1007/BF00336771

Pugh, D., and Woodworth, P. (2014). Sea-Level Science: Understanding Tides, Surges, Tsunamis and Mean Sea-Level Changes . Cambridge: Cambridge University Press. doi: 10.1017/CBO9781139235778. Available online at: https://www.cambridge.org/core/books/sealevel-science/C5E551D95DA4E8AF116FED9F0DEB289B

Rijnsdorp, D. P., Smit, P. B., and Zijlema, M. (2012). Non-hydrostatic modelling of infragravity waves using swash. Coast. Eng. Proc. 1:currents.27. doi: 10.9753/icce.v33.currents.27

Saha, S., Moorthi, S., Pan, H.-L., Wu, X., Wang, J., Nadiga, S., et al. (2010). The ncep climate forecast system reanalysis. Bull. Am. Meteorol. Soc. 91, 1015–1058. doi: 10.1175/2010BAMS3001.1

Sanuy, M., Jiménez, J. A., Ortego, M. I., and Toimil, A. (2020). Differences in assigning probabilities to coastal inundation hazard estimators: Event versus response approaches. J. Flood Risk Manag. 13:e12557. doi: 10.1111/jfr3.12557

Sheppard, C., Dixon, D. J., Gourlay, M., Sheppard, A., and Payet, R. (2005). Coral mortality increases wave energy reaching shores protected by reef flats: examples from the seychelles. Estuarine Coast. Shelf Sci. 64, 223–234. doi: 10.1016/j.ecss.2005.02.016

Solari, S., and Losada, M. A. (2011). Non-stationary wave height climate modeling and simulation. J. Geophys. Res. 116:C09032. doi: 10.1029/2011JC007101

Suzuki, T., Altomare, C., De Roo, S., Vanneste, D., and Mostaert, F. (2018). Manning's Roughness Coefficient in Swash: Application to Overtopping Calculation . FHR Reports. Available online at: https://publicaties.vlaanderen.be/view-file/32905 .

Tolman, H. (2009). User manual and system documentation of wavewatch iii version 3.14. NOAA/NWS/NCEP/MMAB Technical Note 276 , (Appendices), 194.

Tolman, H. (2014). User manual and system documentation of wavewatch iii version 4.18. NOAA/NWS/NCEP/MMAB Technical Note 316 .

Vousdoukas, M. I., Mentaschi, L., Voukouvalas, E., Verlaan, M., and Feyen, L. (2017). Extreme sea levels on the rise along europe's coasts. Earths Fut. 5, 304–323. doi: 10.1002/2016EF000505

Wadey, M., Brown, S., Nicholls, R. J., and Haigh, I. (2017). Coastal flooding in the maldives: an assessment of historic events and their implications. Natural Hazards 89, 131–159. doi: 10.1007/s11069-017-2957-5

Woodroffe, C. D., and Murray-Wallace, C. V. (2012). Sea-level rise and coastal change: the past as a guide to the future. Quatern. Sci. Rev. 54, 4–11. doi: 10.1016/j.quascirev.2012.05.009

Woodworth, P. L. (2005). Have there been large recent sea level changes in the maldive islands? Glob. Planetary Change 49, 1–18. doi: 10.1016/j.gloplacha.2005.04.001

Woodworth, P. L., Melet, A., Marcos, M., Ray, R. D., Wöppelmann, G., Sasaki, Y. N., et al. (2019). Forcing factors affecting sea level changes at the coast. Surveys Geophys. 40, 1351–1397. doi: 10.1007/s10712-019-09531-1

Zahir, H., Asis, M., Rasheed, A., Musthafa, Z. M., Latheef, A. T., and Mohamed, I. (2016). “Second national communication of maldives to the united nations framework convention on climate change,” in Ministry of Environment and Energy. Republic of Maldives: Malé .

Zijlema, M. (2012). “Modelling wave transformation across a fringing reef using swash,” in ICCE 2012: Proceedings of the 33rd International Conference on Coastal Engineering, Santander, Spain, 1-6 July 2012 . Coastal Engineering Research Council. doi: 10.9753/icce.v33.currents.26. Available online at: https://journals.tdl.org/icce/index.php/icce/article/view/6479

Zijlema, M., Stelling, G., and Smit, P. (2011). Swash: an operational public domain code for simulating wave fields and rapidly varied flows in coastal waters. Coast. Eng. 58, 992–1012. doi: 10.1016/j.coastaleng.2011.05.015

Keywords: coastal flooding, wind-waves, sea-level rise, global-to-local modelling, climate services

Citation: Amores A, Marcos M, Pedreros R, Le Cozannet G, Lecacheux S, Rohmer J, Hinkel J, Gussmann G, van der Pol T, Shareef A and Khaleel Z (2021) Coastal Flooding in the Maldives Induced by Mean Sea-Level Rise and Wind-Waves: From Global to Local Coastal Modelling. Front. Mar. Sci. 8:665672. doi: 10.3389/fmars.2021.665672

Received: 08 February 2021; Accepted: 19 May 2021; Published: 21 June 2021.

Reviewed by:

Copyright © 2021 Amores, Marcos, Pedreros, Le Cozannet, Lecacheux, Rohmer, Hinkel, Gussmann, van der Pol, Shareef and Khaleel. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Angel Amores, angel.amores@uib.es

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

Advertisement

Flooding trends and their impacts on coastal communities of Western Cape Province, South Africa

• Published: 25 June 2021
• Volume 87 , pages 453–468, ( 2022 )

Cite this article

• Kaitano Dube   ORCID: orcid.org/0000-0002-7482-3945 1 ,
• Godwell Nhamo 2 &
• David Chikodzi 2  

29k Accesses

41 Citations

22 Altmetric

Explore all metrics

Climate change-induced extreme weather events have been at their worst increase in the past decade (2010–2020) across Africa and globally. This has proved disruptive to global socio-economic activities. One of the challenges that has been faced in this regard is the increased coastal flooding of cities. This study examined the trends and impacts of coastal flooding in the Western Cape province of South Africa. Making use of archival climate data and primary data from key informants and field observations, it emerged that there is a statistically significant increase in the frequency of flooding and consequent human and economic losses from such in the coastal cities of the province. Flooding in urban areas of the Western Cape is a factor of human and natural factors ranging from extreme rainfall, usually caused by persistent cut off-lows, midlatitude cyclones, cold fronts and intense storms. Such floods become compounded by poor drainage caused by vegetative overgrowth on waterways and land pollution that can be traced to poor drainage maintenance. Clogging of waterways and drainage systems enhances the risk of flooding. Increased urbanisation, overpopulation in some areas and non-adherence to environmental laws results in both the affluent and poor settling on vulnerable ecosystems. These include coastal areas, estuaries, and waterways, and this worsens the risk of flooding. The study recommends a comprehensive approach to deal with factors that increase the risk of flooding as informed by the provisions of both the Sustainable Development Goals framework and the Sendai Framework for Disaster Risk Reduction 2015–2030 in a bid to de-risking human settlement in South Africa.

Similar content being viewed by others

Externalities of Climate Change on Urban Flooding of Agartala City, India

Flood risk and adaptation in Indian coastal cities: recent scenarios

Causes and Management of Damaging Flood Incidences in Rapidly Urbanizing Areas of Kathmandu Valley: A Case Study of Flood Event in Bhaktapur District, Nepal

Avoid common mistakes on your manuscript.

Introduction

The world over, many people are resident in coastal areas. The romantic connection between humanity and coastal communities has a long history dating back to the pre-civilisation era. According to Hallegatte et al. ( 2013 ), coastal cities are witnessing an increase in the frequency, intensity and impact of coastal flooding. The cost of flooding can be attributed to several factors such as rapid urbanisation, the increased construction and installation of other assets along the coastal line and climate change (Amoako & Frimpong Boamah, 2015 ; Dhiman et al., 2019 ). Chan ( 2018 ) argue that hydrological hazards faced by coastal cities emanate from a combination of factors such as uncontrolled urban development, climate change, and sea level rise.

Climate change has ushered in a new era of challenges for coastal towns and cities. These areas experience nature’s backlash in the form of intense rainfall, sea level rise, in some instances, tropical cyclones and increasing tidal activity and storm surges (Dube et al., 2020a , 2020b ). The increasing incidence of extreme weather events is worrying as it presents complex challenges for coastal communities' socio-economic development. According to Ogie et al. ( 2018 ), critical coastal infrastructure such as pumps, flood gates, and embankments are particularly vulnerable to increased floods. In addition, transport networks remain vulnerable to coastal flooding (Duy et al., 2019 ). This is likely to threaten the achievement of the global inclusive Sustainable Development Goals (SDGs) that are set to be achieved in 2030 (United Nations, 2015 ).

There is, therefore, a growing consensus and worry that coastal areas are increasingly becoming global hotspots for climate change-induced extreme weather disasters (Chan et al., 2018 ). Balica et al. ( 2012 ) indicate the need to enhance understanding of global vulnerability by explicitly focusing on coastal flooding, which is becoming more common and problematic across the world. Regardless of coastal flooding's recognition as a significant challenge to most areas, the knowledge of the actual extent of climate change risk to coastal areas remains a challenge to most areas in Africa (Kithiia, 2011 ). As a consequence, addressing flood resilience in that context is problematic. According to Handayani et al. ( 2019 ), resilience-building must be a key focus in ensuring coastal areas’ sustainability in the wake of climate change. In light of this call, this study examines and documents the trends and impacts of flooding in the coastal province of Western Cape, South Africa. Although the principal aim of the study is to examine trends and impact of floods in the Western Cape province in general, the main focus will be on urban areas where the greatest socio-econimic impacts occur. Two critical research questions are raised: (1) What has been the long-term flood occurrence in the Western Cape province? (2) What has been the socio-economic impact of these floods on the Western Cape province?.

Literature survey

Extreme weather events remain among the global challenges that both inland and coastal communities must contend with in the quest to ensure sustainable development. Apart from the COVID-19 pandemic, which has had a devastating impact on global economies in 2020 (Nhamo et al., 2020 ), climate change is a wicked problem that the world must battle with going forward if development target aspirations are to be met. The challenge of extreme weather events is particularly pronounced and felt by most developing countries, which still lack the means for adaptation or maladapt (Leal Filho, 2018 , 2019 ; Mirza, 2003 ). In most cases, there is a clear link between communities’ income levels and adaptive capacity. By nature, adaptation requires that nations and states invest more resources into climate change resilience initiatives. Experience has often shown that such resources are often not available for most developing countries, even for basic needs. Therefore, it is anticipated that climate change will likely worsen marginalised communities’ poverty levels due to the impacts pf extreme weather events and costs associated with the damage.

One of the impacts of extreme weather events that has caused challenges for development agencies and planners is the issue of flooding in coastal urban spaces. Besides flooding (a process of submerging of land that is usual dry by overflowing water), coastal communities must battle with other climate change induced challenges such as sea level rise, coastal erosion, ocean pollution, rising sea surface temperature, coral bleaching and severe droughts (IPCC, 2019 ). These coastal challenges have disturbed coastal communities' lives and livelihoods with far-reaching implications for inland communities, which often depends on coastal areas for recreation, food, and other critical supplies. This presents severe challenges for coastal urban communities in Sub-Saharan Africa, where coastal areas are also battling the challenges caused by rapid urbanisation (Cian et al., 2019 ; Dodman et al., 2017 ).

Cities and communities in Southern and Eastern Africa have not been spared from climate change-related hazards, with many cities battling flooding. A study by Braccio ( 2014 ) reveals that in Maputo, a coastal city in Mozambique, there have been increasing incidences of flooding due to the compounded impact of rising sea levels and intense rainfall activity attributed to climate change. As Kabanda ( 2020 ) finds, Mombasa's vulnerability in Kenya due to rising sea level has placed infrastructure such as roads and buildings under flood threat. On the other hand, the threat of flooding in South Africa’s coastal areas is not well documented, with very few studies focussing on the issue (see, for example, Fitchett et al., 2016 ; Dalu et al., 2018 ). This is also the picture across many other places in Southern Africa. Consequently, there are fears that this will curtail the adoption of adequate adaptation and resilience measures.

Despite fears by communities and preliminary evidence of the catastrophic impact of floods in coastal areas there has been little effort to adequately address this challenge. According to Fitchett et al. ( 2016 ), the challenge of coastal flooding is a real perceived threat by tourism businesses operating in the coastal towns of the Eastern Cape province of South Africa. In another study, Dalu et al. ( 2018 ) found that informal settlements that were located on high slopes, degraded slopes and those close to drainage channels were likely to experience significant damages from flooding. This raises concerns as to the impact of such shocks on vulnerable groups and their capacity to recover and adapt from such threats.

Cape Town, which is located in the Western Cape, has not been immune to flooding. Taylor and Davies ( 2019 ) note that the city of Cape Town, the 10th most populous city in Africa often suffers from the impacts of flooding with a devastating impact on railway lines, parking lanes, roads, and power supply and communication infrastructure. Fears are also rife that these impacts will worsen due to climate change induced sea level rise in the city and other areas surrounding it (Dube et al., 2021 ). Due to increased urbanisation, stormwater is also presenting unique challenges for the City of Cape Town (Taylor, 2019 ). Climate change studies have established that there are also fears that with the increased frequency and incidence of the El Niño‐Southern Oscillation in the Southern Hemisphere, there is an anticipation that this will likely see an increased frequency in coastal flooding. Rasmusson and Wallace ( 1983 ), established that the El Niño‐Southern Oscillation is closely linked to sea levels’ variability, which can worsen sea level rise and lead to increased coastal flooding.

Western Cape is one of the most urbanised communities and one of the most unequal societies in South Africa (Gwaze et al., 2018 ). As such the threat of flooding affects different communities differently, with the marginalised communities bearing the brunt of such events. The recent drought in Cape Town exposed the vulnerabilities along these economic and social lines (Enqvist & Ziervogel, 2019 ). Given past experiences, droughts require attention as they often result in mass displacements, which undermines peoples’ livelihood security and infrastructural damage (Dube & Nhamo, 2020a , 2020b ). The devastating impacts of floods were also witnessed in 2019 in Mozambique and other Southern African Development Community (SADC) countries in the wake of Tropical Cyclones Idai and Kenneth (Phiri et al., 2020 ). There is therefore a need for a thorough understanding of flood occurrences and associated risks. Such an undertsnading is more critical now than ever before to allow communities to build resilience and adopt risk reduction measures. In as much as single cases of flood events are documented, there is no study in the SADC area that looks at the long-term trends of floods. Hence, this study examines and documents the trends and impact of floods that have occurred in the Western Cape over the last 120 years. The study seeks to understand flood frequency and its impact on the community, development, and society at large.

Research design

The Western Cape Province is an area located on the southernmost part of South Africa and the African continent (Fig.  1 ). It is the same place that is home to the populous city of Cape Town and the iconic Table Mountain (Dube et al., 2020a , 2020b ). The province lies between coastlines from two oceans namely: the Indian Ocean on the east and the Atlantic Ocean on the west coast. The two oceans separate at the Cape Agulhas. The province has a predominantly Mediterranean climate that is typified by warm and mostly dry summers and cold wet winters. The two oceans play a critical role in shaping the climatic and weather patterns of the area. The Western Cape Province has been in the news for the devastating impacts of extreme weather events, particularly the recent drought of 2017/18 that threatened the water supply system of one of South Africa’s most populous cities and tourism destinations (Dube et al., 2020a , 2020b ). The City of Cape Town and other places in the Western Cape Province are well known for their vulnerability to extreme weather events, with the City of Cape Town often dubbed the “Cape of Storms” by many of its citizens. Rouault, ( 2002 ) notes that the Agulhas Current, whose location is the east coast of South Africa, with a bearing on and off the Eastern and Western Cape coast, is partly responsible for severe weather events in the province.

Source : Authors

Location of Western Cape Province in relation to South Africa and Africa

In Western Cape latent heat fluxes often causes low-level advection of moisture, which in turn causes the intensification of storms and tornadoes, causing flooding. Stramma and Lutjeharms ( 1997 ) noted that the Agulhas Current is one of the most intense western current boundaries in the Southern Hemisphere, and White ( 2000 ) observed two such severe storms during 1998/99 summer on the Agulhas Current. According to Mukheibir and Ziervogel ( 2007 ), the March 2003 and April 2005 intense storms and flooding were reported in Cape Town and the Western Cape province.

A case study research approach was adopted for this study. The study utilised data obtained from the South African Weather Services’ (SAWS) archives for the period 1900 to 2018. Additional data were obtained from field observations and key informant interviews from various Western Cape admimisttrative districts that took place between February and December 2020. A snow ball sampling technique was followed in the selection of 15 key informants, which formed part of the study. Key informants comprised of staff from the City of Cape Town that included planners, environmental engineers, museum curators, protected area personnel, tradtional community leaders and climate experts from the province. Such key informant interviews took between 45 and 60 min. Questions for key infrmants centered on documenting the climate history of the area, experiences with the floods, possible causes and possible solutions to flooding among other key questions pertinent to the study. The use of key informants interviews is an acceptable standard, methodological approach, which has been used in previous similar studies by Lo et al. (2017) and Twongyirwe et al. (2018). The approach can yield valid results and allows researchers to collect high quality data within a short period of time from fewer people in a cost effective manner. This methodological approach also addreses the constraints posed by the COVID-19 pandemic of ensuring phsycical and social distancing as it minimised contact with a lot of people. SAWS is one of the most resourced meteorological organisations in terms of weather stations that boasts a wide array of weather and climate equipment networks (Fig.  2 ).

Some Key assets utilised by South African Weather Services

Data analysis was conducted using XLSTAT 2020.5.1 that was run on a Microsoft Excel sheet. A time series was analysed using the Mann–Kendall trend test to determine the presence of trends. The Confidence interval was set at 95%, and the Significance level was set at 5%. The Mann- Kendall trend test was also used to plot the Sen’s Slope. The Mann–Kendall trend test is a commonly used parametric tool used in climate and hydrological studies that enjoys wide usage and has been used in similar studies by other scholars (Hamed, 2008 ; Hu et al., 2020 ). Choropleth maps showing flood hotspots in the study area were produced in a Geographic Information System using flood incident count at local municipality level as a measure. Frequently flooded areas were denoted by increasing the colour intensity on the map. Primary and secondary qualitative data was analysed using content and thematic analysis.

Results and discussion

The study found that between 1900 and 2018, at least 334 major flood events occurred in the Western Cape, with a mean annual number of floods being 2.9. The highest number of annual flood events over the period of study is 20, which occurred in 2008. The second-highest number of flood events were recorded in 1981, where 15 floods were recorded. The third-highest flood years were recorded in 2004, 2005 and 2006, where 13 floods were recorded in each year. Consequently, the frequency of floods has been higher during the past four decades as compared to earlier periods (Fig.  3 ). In the first half-century, the average number of floods was at less than two flood events per year in the province, with the last century having peaked up to slightly more than four flood events per year. Figure  3 shows that there is a statistically significant ( p  = 0.0001, α = 0.5) increase in the number of flooding events occurring in Western Cape province over the period of study.

Source : Authors, Data from SAWS (2020)

Flooding frequency and trends in Western Cape province 1900–2018

The observed increase in coastal flooding in the Western Cape Province in Fig.  3 confirms earlier findings in other parts of the world where coastal flooding is on the increase due to extreme weather events induced by climate change and other urban challenges as reported by Hirabayashi, ( 2013 ) and also Kim, ( 2017 ). One of the critical drivers of coastal flooding in Western Cape Province is high sea tides and intense rainfall activity. A study by Dube et al. ( 2021 ) found that some of the recent floodings observed in the City of Cape Town, for example, were worsened by sea level rise confirming earlier findings by Park and Lee ( 2020 ). Flooding in the Western Cape Province is worrying as it has far reaching socio-economic impacts on one of the most urbanised provinces and areas in the entire Southern Africa.

The study found that flooding was mainly concentrated in the areas close to the coast, with the highest flood prevalence concentrated around the City of Cape Town and areas that are to the east of the province (Fig.  4 ). Areas to the South East of the Cape Winelands district and areas to the South of the Cape Winelands seems to be most affected by the number of floods, whereas central Eden also experiences the highest number of floods. In the Cape Winelands District, the areas between Montagu and Ashton town are also considerably affected by flooding. The area which lies along the R62 road is prone to flooding due to several factors. The interviews were conducted with key informants where it was revealed that the area is susceptible to flooding due to its mountainous terrain with water being channelled towards a mountain gorge which the R62 road runs through. Other flood hotspots include areas near South East coastal areas of Overberg District east of Cape Agulhas near Strus Bay. In the Garden route area, areas around Plettenberg Bay were identified as flooding hotspots. From Fig.  4 it emerges that floods tend to be concentrated along the coastline. However, by and large, the West Coast and Central Karoo areas are not as affected due to semi-arid and desert conditions that prevail, with flush floods occurring once in a while.

Flood count and risk analysis map of Western Cape province between 1900 and 2018

Information gathered from the key informants revealed that heavy rainfall along the Kogmanskloof Mountain Pass along the R62 road often results in flooding in areas around the pass. Based on evidence from the Western Cape Provincial Government report and key informants in the area, one of the most memorable floods in the area is the Montagu flood of March 2003 which went on to be declared a national disaster. The record flood occurred as a consequence of a cut-off low that resulted in the Montagu area receiving 178 mm of rainfall in 1 day on the 23rd of March 2003. The total monthly rainfall for that month went up to 241 mm, which became one of the wettest days in the history of the area. That particular flood event damaged roads, factories in Ashton town, farms, schools and had a huge impact on tourism. The De Hoop Nature Reserve’s main road was washed away, and Goukamma Nature Reserve access road was also badly damaged in a development that costed Cape Nature more than R1 million. The traditional leadership in the area fears that the flood event and other subsequent floods washed away several archaeological artefacts from the Khoisan San community in mountains in the area leading to a loss of important historical heritage. The flood also had an adverse impact on the Klein Karoo Arts Festival as the area was declared a disaster zone because of that flood event. The access road between Ashton and Montagu was disrupted just in time for the festival cutting off tourist access.

Field observations and information from key informants revealed that given a significantly large basin and water channelled from mountain zones, flood risk is also high in that area. Another factor that promotes occasional floods is that the area seems to be experiencing successive years of flooding and drought, given its geographic location, which is transitional to the central Karoo, which is semi-desert. Pollution from urban and farming activities in the catchment further promotes the heavy growth of weeds within the Kogmanskloofrivier river. This reduces the rate of water outflow from the area and ultimately increases the risk of flooding in the area.

It emerged during fieldwork that the government is working on upgrading road infrastructure in the area so as to mitigate the increased impact of flooding on human settlements and infrastructure. The infrastructure includes elevating the road and making bigger elevated bridges to allow for more water to flow at any given time without causing flooding. The bridge in Ashton town, for example, was being upgraded to allow more water flow. It remains to be seen how such upgrades will limit the disruptions caused by floods to Montagu and Ashton town’s two communities.

Socio-economic impact of floods in Western Cape

It emerged from the SAWS records, damages induced by flooding in the Western Cape ranged from infrastructure (roads, bridges, and rail lines), loss of properties, homes, damages to vineyards, damages to informal settlements, and injury and loss of human lives. In as much as the increased socio-economic and human cost can be tracked back to increased frequency of flooding events, increased urbanisation and affluence has over the years worsened this phenomenon.

Table 1 shows some of the most significant and high impact floods that have been witnessed in the Western Cape between 1901 and 2018. The flooding incidences recorded in various places in the Western Cape show that the flooding events in the province have led to the death of more than 129 people across province. There were very few deaths witnessed before 1980, with only three fatalities attributed to floods. The single highest number of fatalities were recorded in 1981 when a staggering 104 people were killed in a single incident by a raging flood that wiped away almost the entire small town of Laingsburg. On 25 January 1981, a cloud outburst caused one of the greatest floods in the Great Karoo. Given the geohydrological makeup of the area, where the soil cannot absorb much water, the cloud outburst resulted in a 6 m high flood after the Baviaans and Buffels rivers. The two rivers have their confluence in the town, and they bursted their banks, destroying 185 houses and 23 businesses.

That flooding incident went on to be labelled as one of the worst natural disasters in South Africa. In addition to the destruction of properties and businesses, the flood led to the washing away of animals and the town’s tourism infrastructure. During this 1 in 100 year flood incident, the Great Trek Monument, which is an important Dutch historical monument, which was constructed in 1938, was washed away. While the greater part of the monument was recovered after the flood, the monument’s pedestal was lost and was only found after another flood in June 2015. The impacts of floods are well documented, which have played both a positive and negative role in heritage properties (Liu, 2019 ; Reimann, 2018 ). While floods destroyed the monument, they also created another historical monument. Post the flood a Flood Museum was constructed in the same town.

It would appear from key informants’ accounts that the 1981 Laingsburg natural disaster was partial caused settlements that were established without proper risk analysis and consideration. Settlements, which are established without a proper risk assessment in the form of environmental impact assessment remain a worry across the country. This is particularly so, given the additional vulnerabilities induced by climate change-induced weather extreme events. Climate change-induced extreme weather events have the potential to amplify natural events, including rainfall patterns and intensity. Field observation revealed that even after the disaster, a look at the area shows that human development, including commercial infrastructures such as hotels, lodges, restaurants, and a hospital, is still located in flood zone. The adjustment to address the risk is crucial to current and future urban sustainability as part of disaster risk reduction. In that vein, the 2030 Agenda for Sustainable Development, particularly the Sustainable Development Goal Target 11.5, seeks to reduce the number of fatalities and economic losses relative to the gross domestic product caused by disasters, focusing on the poor (United Nations, 2015 ). Similar aspirations are encompassed in the Sendai Framework for Disaster Risk Reduction 2015–2030 (United Nations Office for Disaster Risk Reduction, 2015 ).

The Western Cape Province case study reveals that flood risks in urban areas are on the increase. Such risks primarily affect the poor. Extreme weather events such as floods often destroys homes and livelihoods. Evidence from the study reveals that flooding has in the past destroyed several shacks and homes. The worst affected areas in the past have been areas around George, Cape Town, Hermanus, Cape Flats and Khayelitsha. Apart from the Western Cape Province, similar observations have been made elsewhere in African states and other developing states that are located in coastal areas. Some of the affected areas includes Manila, Philippines (Zoleta-Nantes, 2002 ), Nigeria, (Adelekan, 2010 ; Echendu, 2020 ) and China (Jiang et al., 2018 ).

According to Douglas ( 2008 ) and Douglas ( 2017 ), the unjust water and climate are flooding the poor along with the coastal towns in Africa. The situation can be attributed to increasing urban poverty and rapid urbanisation and urban sprawl that has left many condemned to a life of squalor. Most urban councils in the coastal Western Cape and, in many respects, other urban areas in South Africa are failing to meet the demands of an ever-increasing housing backlog. Consequently, most urban migrants are settled in informal settlements where the settlements are unplanned and often in disaster-prone areas such as waterways and, in some instances, fragile ecosystems prone to flooding and other disasters. In Cape Town, for example, field observations revealed that the mushrooming of informal settlements magnified by the ongoing land grabs in the Cape Flats resulted in many building houses on waterways and fragile ocean sand dunes in densely populated areas, which exposed thousands to flood and fire disasters (Fig.  5 ). Therefore, it is not surprising that the City of Cape Town has witnessed increased incidences and cost of residents' displacement and property loss due to the combined effect of extreme weather events, urban sprawl and invasion of disaster areas by city dwellers.

Source : Authors, Fieldwork 2020

Informal settlement built on unstable dunes and waterway in Khayelitsha, Cape Town

The debate of flooding and climate change becomes central, as flooding disasters are driving many people around the globe into poverty. This sentiment is shared by Jordhus-Lier et al. ( 2019 ), who noted that the City of Cape Town flooding is a growing concern that requires focus and attention by developing climate change adaptation. In doing so, there is a need to address factors that induce vulnerabilities. According to Ribot ( 2014 ), addressing vulnerabilities requires an approach that considers the root causes of the crises so that transformative solutions can be found, often lacking in climate change adaptation studies. In this regard, addressing vulnerabilities must consider various matrices at play. These include climatic factors and factors that push people into settling in eco-sensitive areas and waterways and considering aspects that deal with rapid rural to urban migration. Finally, dealing with aspects of refuse waste and drainage clogging in many urban setups in the Western Cape and across the country. In recent years, urban inequality has featured storngly in the mix, with politics playing a central role in urban settlement issues, resulting in wanton settlement development and land grabs, in some instances in areas that are not suitable for settlement.

A recent study by Dube et al. ( 2020a , 2020b ) noted that flooding in Cape Town was not only a factor of poverty as the affluent were also being hit hard by the compounded effect of sea-level rise and intense storm activity in the coastal city. Addressing vulnerabilities is, therefore, a wicked problem that requires a holistic approach. It is common knowledge that climate change, apart from civil unrest and wars that ravage the continent, is one of the contributory factors and drivers of rural poverty, which drives rural to urban migration. Therefore, addressing sustainability becomes a complex issue that requires the reconfiguration of governance systems to ensure urban transformation in line with the aspirations of SDG11 as espoused by Patel ( 2017 ).

Besides the City of Cape Town, other coastal urban areas have been threatened by floodings, such as George and Hermanus. There are also other important tourist resort towns where millions of rand worth of property have been damaged. The floods have been blamed for the destruction of tourism infrastructure, often located in pristine areas close to nature. Floods in the Western Cape have often cut off routes to some of the province's tourism destinations, such as Agulhas National Park, where the primary link road becomes flooded during intense rainfall as the road runs through a significant wetland area. Flooding, therefore, undermines economic activities in the province. Figure  6 shows the damage which occurred in May 2005 on the R43 highway, which links Hermanus to Stanford.

Source : Overstrand Municipality

Impacts of severe flooding in Hermanus on transport infrastructure.

Looking at the global scale, addressing global warming that leads to climate change, and in turn, weather extreme events, in this case, the threat of flooding, will require both local and national governments to embrace climate change mitigation strategies. This, therefore, demands implementing measures aimed at reducing the carbon footprint of the province and all its metros. The province has an obligation to reduce its emissions under the Paris Agreement, and one way of doing this is an investment in clean energy such as wind and solar, which requires an investment in energy efficiency technologies. Investment in clean energy should address challenges of energy, climate change and unemployment in the province. One of the ways of decreasing disaster vulnerability in Africa is through the addressing of poverty and inequality.

SDG 16 Target 16.3 speaks about the need to ensure the rule of law. This is a critical issue with regards to developing a sustainable urban community within the province of the Western Cape. One of the challenges faced by urban areas in South Africa is non-adherence to city by-laws and national legislative provisions, with environmental laws often being flouted for political expediency. Strict adherence to environmental laws and enforcement of environmental laws can ensure that people do not settle in fragile and eco-sensitive areas such as wetland, waterways and protected coastal zones and estuaries, which are often risky areas. Adherence and enforcement of environmental laws will ensure that some of the populations now located in risk and disaster areas are relocated to safe zones where proper urban planning has been taken into consideration to reduce flood risk.

Colenbrander ( 2019 ) argues that despite the transition to democracy and adopting a white paper on sustainable development fairness and inclusivity, the paper is still elusive regarding reducing risk and vulnerability in coastal management in South Africa. SDG Targets 16.6 and Target 16.7 further speak about ensuring the need to develop effective and transparent, and accountable institutions at all levels. They also speak about the need to foster responsive, inclusive, participatory and representative decision making at all levels. The Western Cape government has often come under fire for directing a considerable share of its resources towards the wealthy elite at the expense of the marginalised (Black et al., 2020 ). This has entrenched and extended inequality in many respects, which has negated the poor to live in squaller conditions. In a bid to reduce risk, the provincial government might need to relook at resource allocation to provide the much needed essential services and deliver on promises of housing for all as a strategy of reducing the housing backlog. This should also provide affordable housing, which will take large segments of the population out of informal settlements. Given the scope and demand for safe housing, there might be a need for the national government, civil society, and private players to roll out housing for the poor and low, middle-income earners who are often at the receiving end of the flooding disasters that affect the province. While there is evidence (Fig.  7 ) that there has been an increase in people living in formal housing, there is a need to arrest the increasing number of people living in informal settlements, most of whom are at the mercy of extreme weather events such as flooding in the Western Cape. A reduction in housing backlog is one good starting point. The Western Cape’s housing backlog is estimated at a staggering 600,000 as of the year 2020, according to a report by Gontsana ( 2020 ).

Source : Authors, Data from Stats SA

Western Cape Household by dwelling type 1995–2016.

One of the challenges that are likely to be faced in housing is the issue of land to relocate people located in climate disaster zones. Releasing state land for human settlement to construct affordable housing and rural development houses is a must in addressing the problem. This has to be done in a holistic manner that does not seek to score cheap political points, as we have seen during the Day Zero drought phenomenon (Nhamo & Agyepong, 2019 ). One other problem from flooding has been the clogging of water systems with either overgrown vegetation or waste, or both. Work by Echendu ( 2020 ) in Nigeria, Abass et al. ( 2020 ) in Ghana, Mahmood et al. ( 2017 ) in Khartoum, and Dalu et al. ( 2018 ) in the Eastern Cape, South Africa, show that poor drainage and drainage clogging, compounds flooding in urban areas. The Western Cape is not unique, as in high density suburbs, the infrastructure maintenance and refuse collection is rather lax. The phenomenon has worsened the impacts of flooding in the city with calls for dredging of weeds overgrowth in waterways; improved refuse collection and waste management calls being made to ensure that there is a substantial reduction of risk of flooding.

Conclusions

The study sought to investigate the trends and impacts of floods in the Western Cape Province of South Africa. Making use of the Mann–Kendall Trend test, the study established that there is a statistically significant increase in the number of flood events that are taking place in the Western Cape province. The study also found that some of the most vulnerable areas to flooding includes Knysna, George, Hermanus and cape flats in Cape Town, to mention but a few. Floods compounded with other urban challenges have led to an increase in the human and economic costs of floods, with some floods costing millions and, in some cases, billions of rand. The loss of property, infrastructure and human lives makes floods an urgent concern that requires urgent attention from development practitioners, city planners, government and ordinary residents to ensure sustainability. Given that flood risk is a result of multiple factors that interact to produce disaster situations for mainly urban areas, there is a need for concerted efforts to put in place measures that build community resilience to floods and build back better thereby producing climate smart societies. The study recommends an integrated approach to the management of flooding in the Western Cape province as part of ensuring urban sustainability. Addressing the flooding challenges further requires a holistic approach that takes into account climate change and other urban challenges such as land grabs, urban sprawling and associated challenges. Lastly, both the private and public sector players need to work together to build climate start infrastructure and insure critical infrastructure against flood hazards given their significant increase over time.

Abass, K., Buor, D., Afriyie, K., Dumedah, G., Segbefi, A. Y., Guodaar, L., Garsonu, E. K., Adu-Gyamfi, S., Forkuor, D., Ofosu, A., & Gyasi, R. M. (2020). Urban sprawl and green space depletion: Implications for flood incidence in Kumasi, Ghana. International Journal of Disaster Risk Reduction, 51 (2), 433.

Google Scholar  

Adelekan, I. O. (2010). Vulnerability of poor urban coastal communities to flooding in Lagos Nigeria. Environment and Urbanization, 22 (2), 433–450.

Article   Google Scholar  

Amoako, C., & Frimpong Boamah, E. (2015). The three-dimensional causes of flooding in Accra, Ghana. International Journal of Urban Sustainable Development, 7 (1), 109–129.

Balica, S. F., Wright, N. G., & Van der Meulen, F. (2012). A flood vulnerability index for coastal cities and its use in assessing climate change impacts. Natural Hazards, 64 (1), 73–105.

Black, G. F., Liedeman, R., & Ryklief, F. (2020). Using hand maps to understand how intersecting inequalities affect possibilities for community safety in Cape Town. Community Development Journal, 55 (1), 26–44.

Braccio, S. (2014). Flood-prone areas due to heavy rains and sea level rise in the municipality of Maputo. Climate change vulnerability in Southern African cities (pp. 171–185). Cham: Springer. https://doi.org/10.1007/978-3-319-00672-7_11 .

Chapter   Google Scholar  

Cian, F., Blasco, J., & Carrera, L. (2018). Towards resilient flood risk management for Asian coastal cities: Lessons learned from Hong Kong and Singapore. Journal of Cleaner Production, 187 (3), 576–589.

Cian, F., Blasco, J. M. D., & Carrera, L. (2019). Sentinel-1 for monitoring land subsidence of coastal cities in Africa using PSInSAR: A methodology based on the integration of SNAP and staMPS. Geosciences, 9 (3), 124.

Colenbrander, D. (2019). Dissonant discourses: Revealing South Africa’s policy-to-praxis challenges in the governance of coastal risk and vulnerability. Journal of Environmental Planning and Management, 62 (10), 1782–1801.

Dalu, M. T., Shackleton, C. M., & Dalu, T. (2018). Influence of land cover, proximity to streams and household topographical location on flooding impact in informal settlements in the Eastern Cape, South Africa. International Journal of Disaster Risk Reduction, 28 , 481–490. https://doi.org/10.1016/j.ijdrr.2017.12.009 .

Dhiman, R., VishnuRadhan, R., Eldho, T. I., & Inamdar, A. (2019). Flood risk and adaptation in Indian coastal cities: Recent scenarios. Applied Water Science, 9 (1), 5.

Dodman, D., Leck, H., Rusca, M., & Colenbrander, S. (2017). African urbanisation and urbanism: Implications for risk accumulation and reduction. International Journal of Disaster Risk Reduction, 26 , 7–15. https://doi.org/10.1016/j.ijdrr.2017.06.029 .

Douglas, I. (2017). Flooding in African cities, scales of causes, teleconnections, risks, vulnerability and impacts. International Journal of Disaster Risk Reduction, 26 (1), 34–42.

Douglas, I., Alam, K., Maghenda, M., Mcdonnell, Y., McLean, L., & Campbell, J. (2008). Unjust waters: climate change, flooding and the urban poor in Africa. Environment and urbanization, 20 (1), 187–205.

Dube, K., & Nhamo, G. (2020a). Evidence and impact of climate change on South African national parks. Potential implications for tourism in the Kruger National park. Environmental Development, 33 , 1–11. https://doi.org/10.1016/j.envdev.2019.100485 .

Dube, K., & Nhamo, G. (2020b). Vulnerability of nature-based tourism to climate variability and change: Case of Kariba resort town, Zimbabwe. Journal of Outdoor Recreation and Tourism, 29 , 100281. https://doi.org/10.1016/j.jort.2020.100281 .

Dube, K., Nhamo, G., & Chikodzi, D. (2020). Climate change-induced droughts and tourism: Impacts and responses of Western Cape province, South Africa. Journal of Outdoor Recreation and Tourism . https://doi.org/10.1016/j.jort.2020.100319

Dube, K., Nhamo, G., & Chikodzi, D. (2021). Rising sea level and its implications on coastal tourism development in Cape Town, South Africa. Journal of Outdoor Recreation and Tourism, 33 , 100346. https://doi.org/10.1016/j.jort.2020.100346 .

Dube, K., Nhamo, G., & Mearns, K. (2020). &Beyond’s Response to the twin challenges of pollution and climate change in the context of SDGs. In G. Nhamo, G. Odularu, & V. Mjimba (Eds.), Scaling up SDGs implementation. Sustainable development goals series (pp. 87–98). Cham: Springer. https://doi.org/10.1007/978-3-030-33216-7_6 .

Duy, P. N., Chapman, L., & Tight, M. (2019). Resilient transport systems to reduce urban vulnerability to floods in emerging-coastal cities: A case study of Ho Chi Minh city Vietnam. Travel Behaviour and Society, 15 , 28–43. https://doi.org/10.1016/j.tbs.2018.11.001 .

Echendu, A. J. (2020). The impact of flooding on Nigeria’s sustainable development goals (SDGs). Ecosystem Health and Sustainability, 6 (1), 1791735.

Enqvist, J. P., & Ziervogel, G. (2019). Water governance and justice in Cape Town: An overview. Wiley Interdisciplinary Reviews: Water, 6 (4), e1354.

Fitchett, J. M., Grant, B., & Hoogendoorn, G. (2016). Climate change threats to two low-lying South African coastal towns: Risks and perceptions. South African Journal of Science, 112 (5–6), 1–9.

Gontsana, M., 2020. Daily Maverick . [Online] Available at: Retrieved from 4 January 2021 https://www.dailymaverick.co.za/article/2020-03-26-housing-backlog-exceeds-half-a-million-in-western-cape/ .

Gwaze, A., Hsu, T. T., Bosch, T., & Luckett, S. (2018). The social media ecology of spatial inequality in Cape Town: Twitter and instagram. Global Media Journal-African Edition, 11 (1), 1–20.

Hallegatte, S., Green, C., Nicholls, R. J., & Corfee-Morlot, J. (2013). Future flood losses in major coastal cities. Nature Climate Change, 3 (9), 802–806.

Hamed, K. H. (2008). Trend detection in hydrologic data: The Mann–Kendall trend test under the scaling hypothesis. Journal of Hydrology, 349 (3–4), 350–363.

Handayani, W., Fisher, M. R., Rudiarto, I., Setyono, J. S., & Foley, D. (2019). Operationalizing resilience: A content analysis of flood disaster planning in two coastal cities in Central Java, Indonesia. International Journal of Disaster Risk Reduction, 35 , 101073. https://doi.org/10.1016/j.ijdrr.2019.101073 .

Hirabayashi, Y., Mahendran, R., Koirala, S., Konoshima, L., Yamazaki, D., Watanabe, S., Kim, H., & Kanaen, S. (2013). Global flood risk under climate change. Nature Climate Change, 3 (9), 816–821.

Hu, Z., Liu, S., Zhong, G., Lin, H., & Zhou, Z. (2020). Modified Mann-Kendall trend test for hydrological time series under the scaling hypothesis and its application. Hydrological Sciences Journal, 45 (14), 2419.

IPCC, 2019. Special report on the ocean and cryosphere in a changing climate, s.l.: IPCC.

Jiang, Y., Zevenbergen, C., & Ma, Y. (2018). Urban pluvial flooding and stormwater management: A contemporary review of China’s challenges and “sponge cities” strategy. Environmental Science & Policy, 80 , 132–143. https://doi.org/10.1016/j.envsci.2017.11.016 .

Jordhus-Lier, D., Saaghus, A., Scott, D., & Ziervogel, G. (2019). Adaptation to flooding, pathway to housing or ‘wasteful expenditure’? Governance configurations and local policy subversion in a flood-prone informal settlement in Cape Town. Geoforum, 98 , 55–65. https://doi.org/10.1016/j.geoforum.2018.09.029 .

Kabanda, T. (2020). GIS modeling of flooding exposure in Dar es Salaam coastal areas. African Geographical Review, 39 (2), 134–143.

Kim, Y., Eisenberg, D. A., Bondank, E. N., Chester, M. V., Giuseppe Mascaro, B., & Underwood, S. (2017). Fail-safe and safe-to-fail adaptation: decision-making for urban flooding under climate change. Climatic Change, 145 (3–4), 397–412.

Kithiia, J. (2011). Climate change risk responses in East African cities: Need, barriers and opportunities. Current Opinion in Environmental Sustainability, 3 (3), 176–180.

Leal Filho, W., Balogun, A. L., Ayal, D. Y., Bethurem, E. M., Murambadoro, M., Mambo, J., & Mugabe, P. (2018). Strengthening climate change adaptation capacity in Africa-case studies from six major African cities and policy implications. Environmental Science & Policy, 86 , 29–37. https://doi.org/10.1016/j.envsci.2018.05.004 .

Leal Filho, W., Balogun, A. L., Olayide, O. E., Azeiteiro, U. M., Ayal, D. Y., Muñoz, P. D., & Saroar, M. (2019). Assessing the impacts of climate change in cities and their adaptive capacity: Towards transformative approaches to climate change ada. Science of The Total Environment, 692 , 1175–1190. https://doi.org/10.1016/j.scitotenv.2019.07.227 .

Liu, J., Xu, Z., Chen, F., Chen, F., & Zhang, L. (2019). Flood hazard mapping and assessment on the Angkor world heritage site Cambodia. Remote Sensing, 11 (1), 98.

Mahmood, M. I., Elagib, N. A., Horn, F., & Saad, S. A. (2017). Lessons learned from Khartoum flash flood impacts: An integrated assessment. Science of the Total Environment, 601 , 1031–1045. https://doi.org/10.1016/j.scitotenv.2017.05.260 .

Mirza, M. M. Q. (2003). Climate change and extreme weather events: Can developing countries adapt? Climate Policy, 3 (3), 233–248.

Mukheibir, P., & Ziervogel, G. (2007). Developing a municipal adaptation plan (MAP) for climate change: The city of Cape Town. Environment and Urbanization, 19 (1), 143–158.

Nhamo, G., & Agyepong, A. O. (2019). Climate change adaptation and local government: Institutional complexities surrounding Cape Town’s day zero. Jàmbá: Journal of Disaster Risk Studies, 11 (3), 1–9.

Nhamo, G., Dube, K., & Chikodzi, D. (2020). Counting the Cost of COVID-19 on the global tourism industry (1st ed.). Switzerlerland: Springer International Publishing. https://doi.org/10.1007/978-3-030-56231-1 .

Book   Google Scholar  

Ogie, R. I., Holderness, T., Dunn, S., & Turpin, E. (2018). Assessing the vulnerability of hydrological infrastructure to flood damage in coastal cities of developing nations. Computers, Environment and Urban Systems, 68 , 97–109. https://doi.org/10.1016/j.compenvurbsys.2017.11.004 .

Park, S. J., & Lee, D. K. (2020). Prediction of coastal flooding risk under climate change impacts in South Korea using machine learning algorithms. Environmental Research Letters, 15 (9), 094052.

Patel, Z., Greyling, S., Simon, D., Arfvidsson, H., Moodley, N., Primo, N., & Wright, C. (2017). Local responses to global sustainability agendas: learning from experimenting with the urban sustainable development goal in Cape Town. Sustainability science, 12 (5), 785–797.

Phiri, D., Simwanda, M., & Nyirenda, V. (2020). Mapping the impacts of cyclone Idai in Mozambique using Sentinel-2 and OBIA approach. South African Geographical Journal, 103 (2), 237–258.

Rasmusson, E. M., & Wallace, J. M. (1983). Meteorological aspects of the El Nino/southern oscillation. Science, 4629 (222), 1195–1202.

Reimann, L., Vafeidis, A. T., Brown, S., Hinkel, J., & Tol, R. S. J. (2018). Mediterranean UNESCO world heritage at risk from coastal flooding and erosion due to sea-level rise. Nature communications, 9 (1), 1–11.

Ribot, J. (2014). Cause and response: Vulnerability and climate in the Anthropocene. The Journal of Peasant Studies, 41 (5), 667–705.

Rouault, M., White, S. A., Reason, C. J. C., Lutjeharms, J. R. E., & Jobard, I. (2002). Ocean–atmosphere interaction in the Agulhas current region and a South African extreme weather event. Weather and Forecasting, 17 (4), 655–669.

South African Weather Service , 2019. Annual state of climate 2019, s.l.: South African Weather Service.

Stramma, L., & Lutjeharms, J. (1997). The flow field of the subtropical gyre of the South Indian Ocean. Journal of Geophysical Research, 102 (C3), 5513–5530.

Taylor, A. (2019). Managing stormwater and flood risk in a changing climate: Charting urban adaptation pathways in Cape Town. In D. Scott, H. Davies, & M. New (Eds.), Mainstreaming climate change in urban development: Lessons from Cape Town (pp. 224–241). Cape Town: Cape Town University Press.

Taylor, A. & Davies, H., 2019. An overview of climate change and urban development in cape town. Climate change and urban development: lessons from Cape Town. Cape Town: UCT Press.

United Nations, 2015. Agenda 2030 on sustainable development . [Online] Available at: Retrieved from 11 July 2020 https://sustainabledevelopment.un.org/content/documents/21252030%20Agenda%20for%20Sustainable%20Development%20web.pdf .

United Nations Office for Disaster Risk Reduction, 2015. Sendai Framework for Disaster Risk Reduction 2015–2030, s.l.: United Nations Office for Disaster Risk Reduction.

White, S. A., 2000. The influence of the Agulhas Current on two South African extreme weather events , Cape Town: (Doctoral dissertation, University of Cape Town)..

Zoleta-Nantes, D. B. (2002). Differential impacts of flood hazards among the street children, the urban poor and residents of wealthy neighborhoods in Metro Manila, Philippines. Mitigation and Adaptation Strategies for Global Change, 7 (3), 239–266.

Download references

Author information

Authors and affiliations.

Department of Ecotourism Management, Vaal University of Technology, Private Bag X021, Vanderbijlpark, 1911, South Africa

Kaitano Dube

Institute of Corporate Citizenship, University of South Africa, PO Box 392 Pretoria 002, Pretoria, South Africa

Godwell Nhamo & David Chikodzi

You can also search for this author in PubMed   Google Scholar

Corresponding author

Correspondence to Kaitano Dube .

Ethics declarations

Conflict of interest.

There is no conflict of interest in conducting and writing the article.

Compliance with ethical standards

This serves to declare that myself Kaitano Dube on my behalf and on behalf of the co-authors Godwell Nhamo and David Chikodzi all from University of South Africa are the sole authors of the article Trends and impacts of floods in coastal communities of the Western Cape province in South Africa which we have submitted for publication consideration in GeoJournal. All the authors participated enough to be considered authors of the article. We further attest that all third-party material has been acknowledged. The research was conducted in line with ethical provisions as provided by researcher institutions.

Additional information

Publisher's note.

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Reprints and permissions

About this article

Dube, K., Nhamo, G. & Chikodzi, D. Flooding trends and their impacts on coastal communities of Western Cape Province, South Africa. GeoJournal 87 (Suppl 4), 453–468 (2022). https://doi.org/10.1007/s10708-021-10460-z

Download citation

Accepted : 15 June 2021

Published : 25 June 2021

Issue Date : October 2022

DOI : https://doi.org/10.1007/s10708-021-10460-z

Share this article

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Coastal flooding
• Natural hazards
• Western Cape
• Climate change
• Find a journal
• Publish with us
• Track your research

Information

• Author Services

Initiatives

You are accessing a machine-readable page. In order to be human-readable, please install an RSS reader.

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited. For more information, please refer to https://www.mdpi.com/openaccess .

Feature papers represent the most advanced research with significant potential for high impact in the field. A Feature Paper should be a substantial original Article that involves several techniques or approaches, provides an outlook for future research directions and describes possible research applications.

Feature papers are submitted upon individual invitation or recommendation by the scientific editors and must receive positive feedback from the reviewers.

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

Original Submission Date Received: .

• Active Journals
• Find a Journal
• Proceedings Series
• For Authors
• For Reviewers
• For Editors
• For Librarians
• For Publishers
• For Societies
• For Conference Organizers
• Open Access Policy
• Institutional Open Access Program
• Special Issues Guidelines
• Editorial Process
• Research and Publication Ethics
• Article Processing Charges
• Testimonials
• Preprints.org
• SciProfiles
• Encyclopedia

Article Menu

• Subscribe SciFeed
• Recommended Articles
• Google Scholar
• on Google Scholar
• Table of Contents

Find support for a specific problem in the support section of our website.

Please let us know what you think of our products and services.

Visit our dedicated information section to learn more about MDPI.

JSmol Viewer

Long-term dynamic of land reclamation and its impact on coastal flooding: a case study in xiamen, china.

1. Introduction

2. materials and methods, 2.1. study area, 2.2. methods, 2.2.1. methodology overview, 2.2.2. coastline and land reclamation extraction, 2.2.3. coastal flood modeling and exposure analysis, 3.1. dynamics and drivers of sea reclamation, 3.2. impact of land reclamation on coastal inundation, 3.3. impact of sea reclamation on population exposure, 3.4. extra pressures from future sea-level rise, 4. discussion, 4.1. explanation of results, 4.2. implications for coastal flood resilience and adaptation, 4.3. limitations, 5. conclusions, author contributions, conflicts of interest.

• Sengupta, D.; Chen, R.; Meadows, M.E. Building beyond land: An overview of coastal land reclamation in 16 global megacities. Appl. Geogr. 2018 , 90 , 229–238. [ Google Scholar ] [ CrossRef ]
• Lai, L.W.C.; Chau, K.W.; Lorne, F.T. “Forgetting by not doing”: An institutional memory inquiry of forward planning for land production by reclamation. Land Use Policy 2019 , 82 , 796–806. [ Google Scholar ] [ CrossRef ]
• Meng, W.; Hu, B.; He, M.; Liu, B.; Mo, X.; Li, H.; Wang, Z.; Zhang, Y. Temporal-spatial variations and driving factors analysis of coastal reclamation in China. Estuar. Coast. Shelf Sci. 2017 , 191 , 39–49. [ Google Scholar ] [ CrossRef ]
• Zhang, Y.; Chen, R.; Wang, Y. Tendency of land reclamation in coastal areas of Shanghai from 1998 to 2015. Land Use Policy 2020 , 91 , 104370. [ Google Scholar ] [ CrossRef ]
• Duan, H.; Zhang, H.; Huang, Q.; Zhang, Y.; Hu, M.; Niu, Y.; Zhu, J. Characterization and environmental impact analysis of sea land reclamation activities in China. Ocean Coast. Manag. 2016 , 130 , 128–137. [ Google Scholar ] [ CrossRef ]
• Li, F.; Ding, D.; Chen, Z.; Chen, H.; Shen, T.; Wu, Q.; Zhang, C. Change of sea reclamation and the sea-use management policy system in China. Mar. Policy 2020 , 115 , 103861. [ Google Scholar ] [ CrossRef ]
• Stocker, T. Climate Change 2013: The Physical Science Basis: Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change ; Cambridge University Press: Cambridge, UK, 2014. [ Google Scholar ]
• Garner, A.J.; Mann, M.E.; Emanuel, K.A.; Kopp, R.E.; Lin, N.; Alley, R.B.; Horton, B.P.; DeConto, R.M.; Donnelly, J.P.; Pollard, D. Impact of climate change on New York City’s coastal flood hazard: Increasing flood heights from the preindustrial to 2300 CE. Proc. Natl. Acad. Sci. USA 2017 , 114 , 11861–11866. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Marsooli, R.; Lin, N.; Emanuel, K.; Feng, K. Climate change exacerbates hurricane flood hazards along US Atlantic and Gulf Coasts in spatially varying patterns. Nat. Commun. 2019 , 10 , 3785. [ Google Scholar ] [ CrossRef ] [ PubMed ] [ Green Version ]
• Vousdoukas, M.I.; Mentaschi, L.; Voukouvalas, E.; Bianchi, A.; Dottori, F.; Feyen, L. Climatic and socioeconomic controls of future coastal flood risk in Europe. Nat. Clim. Chang. 2018 , 8 , 776–780. [ Google Scholar ] [ CrossRef ]
• Knutson, T.R.; McBride, J.L.; Chan, J.; Emanuel, K.; Holland, G.; Landsea, C.; Held, I.; Kossin, J.P.; Srivastava, A.K.; Sugi, M. Tropical cyclones and climate change. Nat. Geosci. 2010 , 3 , 157–163. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Peduzzi, P.; Chatenoux, B.; Dao, H.; De Bono, A.; Herold, C.; Kossin, J.; Mouton, F.; Nordbeck, O. Global trends in tropical cyclone risk. Nat. Clim. Chang. 2012 , 2 , 289–294. [ Google Scholar ] [ CrossRef ]
• Forman, R.T.T.; Wu, J.G. Where to put the next billion people. Nature 2016 , 537 , 608–611. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Woodruff, J.D.; Irish, J.L.; Camargo, S.J. Coastal flooding by tropical cyclones and sea-level rise. Nature 2013 , 504 , 44–52. [ Google Scholar ] [ CrossRef ] [ PubMed ] [ Green Version ]
• Loures, L.; Crawford, P. Democracy in progress: Using public participation in post-industrial landscape (re)-development. WSEAS Trans. Environ. Dev. 2008 , 4 , 794–803. [ Google Scholar ]
• Loures, L.; Panagopoulos, T. Reclamation of derelict industrial land in Portugal: Greening is not enough. Int. J. Sustain. Dev. Plan. 2010 , 5 , 343–350. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Wang, X.G.; Su, F.Z.; Zhang, J.J.; Cheng, F.; Hu, W.Q.; Ding, Z. Construction land sprawl and reclamation in the Johor River Estuary of Malaysia since 1973. Ocean Coast. Manag. 2019 , 171 , 87–95. [ Google Scholar ] [ CrossRef ]
• Tian, B.; Wu, W.; Yang, Z.; Zhou, Y. Drivers, trends, and potential impacts of long-term coastal reclamation in China from 1985 to 2010. Estuar. Coast. Shelf Sci. 2016 , 170 , 83–90. [ Google Scholar ] [ CrossRef ]
• Xue, X.; Hong, H.; Charles, A.T. Cumulative environmental impacts and integrated coastal management: The case of Xiamen, China. J. Environ. Manage. 2004 , 71 , 271–283. [ Google Scholar ] [ CrossRef ]
• Sousa, C.A.M.; Cunha, M.E.; Ribeiro, L. Tracking 130 years of coastal wetland reclamation in Ria Formosa, Portugal: Opportunities for conservation and aquaculture. Land Use Policy 2020 , 94 , 104544. [ Google Scholar ] [ CrossRef ]
• Wu, W.; Yang, Z.; Tian, B.; Huang, Y.; Zhou, Y.; Zhang, T. Impacts of coastal reclamation on wetlands: Loss, resilience, and sustainable management. Estuar. Coast. Shelf Sci. 2018 , 210 , 153–161. [ Google Scholar ] [ CrossRef ]
• Ewers Lewis, C.J.; Baldock, J.A.; Hawke, B.; Gadd, P.S.; Zawadzki, A.; Heijnis, H.; Jacobsen, G.E.; Rogers, K.; Macreadie, P.I. Impacts of land reclamation on tidal marsh ‘blue carbon’ stocks. Sci. Total Environ. 2019 , 672 , 427–437. [ Google Scholar ] [ CrossRef ]
• Slamet, N.S.; Dargusch, P.; Aziz, A.A.; Wadley, D. Mangrove vulnerability and potential carbon stock loss from land reclamation in Jakarta Bay, Indonesia. Ocean Coast. Manag. 2020 , 195 , 105283. [ Google Scholar ] [ CrossRef ]
• China Daily News. Land Reclamation from Sea Worthwhile? Available online: http://www.chinadaily.com.cn/bizchina/2010-06/26/content_10024448.htm (accessed on 1 February 2021).
• Nanfang Metropolis Daily News. A Serious Foundation Pit Slope Sliding Accident Resulted from the Soft Soil—A Construction Site at Qianhai Zone in Shenzhen. Available online: http://sz.house.qq.com/a/20150712/008933_1.htm (accessed on 3 February 2021).
• Ding, Y.; Wei, H. Modeling the impact of land reclamation on storm surges in Bohai Sea, China. Nat. Hazards 2017 , 85 , 559–573. [ Google Scholar ] [ CrossRef ]
• Gao, G.D.; Wang, X.H.; Bao, X.W. Land reclamation and its impact on tidal dynamics in Jiaozhou Bay, Qingdao, China. Estuar. Coast. Shelf Sci. 2014 , 151 , 285–294. [ Google Scholar ] [ CrossRef ]
• Song, D.; Wang, X.H.; Zhu, X.; Bao, X. Modeling studies of the far-field effects of tidal flat reclamation on tidal dynamics in the East China Seas. Estuar. Coast. Shelf Sci. 2013 , 133 , 147–160. [ Google Scholar ] [ CrossRef ]
• Benassai, G.; Di Paola, G.; Aucelli, P.P.C. Coastal risk assessment of a micro-tidal littoral plain in response to sea level rise. Ocean Coast. Manag. 2015 , 104 , 22–35. [ Google Scholar ] [ CrossRef ]
• Huang, Z.; Zong, Y.; Zhang, W. Coastal Inundation due to Sea Level Rise in the Pearl River Delta, China. Nat. Hazards 2004 , 33 , 247–264. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Neumann, J.E.; Emanuel, K.A.; Ravela, S.; Ludwig, L.C.; Verly, C. Risks of Coastal Storm Surge and the Effect of Sea Level Rise in the Red River Delta, Vietnam. Sustainability 2015 , 7 , 6553–6572. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Rizzi, J.; Torresan, S.; Zabeo, A.; Critto, A.; Tosoni, A.; Tomasin, A.; Marcomini, A. Assessing storm surge risk under future sea-level rise scenarios: A case study in the North Adriatic coast. J. Coast. Conserv. 2017 , 21 , 453–471. [ Google Scholar ] [ CrossRef ]
• Jongman, B.; Ward, P.J.; Aerts, J.C.J.H. Global exposure to river and coastal flooding: Long term trends and changes. Glob. Environ. Chang 2012 , 22 , 823–835. [ Google Scholar ] [ CrossRef ]
• Neumann, B.; Vafeidis, A.T.; Zimmermann, J.; Nicholls, R.J. Future Coastal Population Growth and Exposure to Sea-Level Rise and Coastal Flooding—A Global Assessment. PLoS ONE 2015 , 10 , e0118571. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Du, S.; Scussolini, P.; Ward, P.J.; Zhang, M.; Wen, J.; Wang, L.; Koks, E.; Diaz-Loaiza, A.; Gao, J.; Ke, Q.; et al. Hard or soft flood adaptation? Advantages of a hybrid strategy for Shanghai. Glob. Environ. Chang. 2020 , 61 , 102037. [ Google Scholar ] [ CrossRef ]
• Wang, J.; Gao, W.; Xu, S.; Yu, L. Evaluation of the combined risk of sea level rise, land subsidence, and storm surges on the coastal areas of Shanghai, China. Clim. Chang. 2012 , 115 , 537–558. [ Google Scholar ] [ CrossRef ]
• Yin, J.; Yin, Z.-e.; Hu, X.-m.; Xu, S.-y.; Wang, J.; Li, Z.-h.; Zhong, H.-d.; Gan, F.-b. Multiple scenario analyses forecasting the confounding impacts of sea level rise and tides from storm induced coastal flooding in the city of Shanghai, China. Environ. Earth Sci. 2011 , 63 , 407–414. [ Google Scholar ] [ CrossRef ]
• Yin, J.; Yu, D.; Yin, Z.; Wang, J.; Xu, S. Modelling the combined impacts of sea-level rise and land subsidence on storm tides induced flooding of the Huangpu River in Shanghai, China. Clim. Chang. 2013 , 119 , 919–932. [ Google Scholar ] [ CrossRef ]
• Diaz, D.B. Estimating global damages from sea level rise with the Coastal Impact and Adaptation Model (CIAM). Clim. Chang. 2016 , 137 , 143–156. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Tamura, M.; Kumano, N.; Yotsukuri, M.; Yokoki, H. Global assessment of the effectiveness of adaptation in coastal areas based on RCP/SSP scenarios. Clim. Chang. 2019 , 152 , 363–377. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Hinkel, J.; Lincke, D.; Vafeidis, A.T.; Perrette, M.; Nicholls, R.J.; Tol, R.S.J.; Marzeion, B.; Fettweis, X.; Ionescu, C.; Levermann, A. Coastal flood damage and adaptation costs under 21st century sea-level rise. Proc. Natl. Acad. Sci. USA 2014 , 111 , 3292–3297. [ Google Scholar ] [ CrossRef ] [ PubMed ] [ Green Version ]
• Peng, B.; Lin, C.; Jin, D.; Rao, H.; Jiang, Y.; Liu, Y. Modeling the total allowable area for coastal reclamation: A case study of Xiamen, China. Ocean Coast. Manag. 2013 , 76 , 38–44. [ Google Scholar ] [ CrossRef ]
• Ghaderpour, E. Some Equal-area, Conformal and Conventional Map Projections: A Tutorial Review. J. Appl. Geod. 2016 , 10 , 197–209. [ Google Scholar ] [ CrossRef ]
• Karney, C.F.F. Transverse Mercator with an accuracy of a few nanometers. J. Geod. 2011 , 85 , 475–485. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Xu, L.; He, Y.; Huang, W.; Cui, S. A multi-dimensional integrated approach to assess flood risks on a coastal city, induced by sea-level rise and storm tides. Environ. Res. Lett. 2016 , 11 , 014001. [ Google Scholar ]
• McFadden, L.; Spencer, T.; Nicholls, R.J. Broad-scale modelling of coastal wetlands: What is required? Hydrobiologia 2007 , 577 , 5–15. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Adnan, M.S.G.; Talchabhadel, R.; Nakagawa, H.; Hall, J.W. The potential of Tidal River Management for flood alleviation in South Western Bangladesh. Sci. Total Environ. 2020 , 731 , 138747. [ Google Scholar ] [ CrossRef ]
• Apel, H.; Aronica, G.T.; Kreibich, H.; Thieken, A.H. Flood risk analyses—how detailed do we need to be? Nat. Hazards 2009 , 49 , 79–98. [ Google Scholar ] [ CrossRef ]
• Fang, J.; Lincke, D.; Brown, S.; Nicholls, R.J.; Wolff, C.; Merkens, J.-L.; Hinkel, J.; Vafeidis, A.T.; Shi, P.; Liu, M. Coastal flood risks in China through the 21st century–an application of DIVA. Sci. Total Environ. 2020 , 704 , 135311. [ Google Scholar ] [ CrossRef ]
• Kulp, S.; Strauss, B.H. Rapid escalation of coastal flood exposure in US municipalities from sea level rise. Clim. Chang. 2017 , 142 , 477–489. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Xiamen Municipal Bureau of Nature Resoureces and Planning. Xiamen Master Planning 2017–2035. Available online: http://zygh.xm.gov.cn/zwgk/zdxxgk/ghcg/ztgh/202001/t20200113_2499452.htm (accessed on 12 October 2020).
• Ministry of Natural Resources, PRC. 2019 China Sea Level Bulletin. Available online: http://gi.mnr.gov.cn/202004/t20200430_2510978.html (accessed on 21 December 2020).
• Hoegh-Guldberg, O.; Jacob, D.; Taylor, M.; Bolaños, T.G.; Bindi, M.; Brown, S.; Camilloni, I.A.; Diedhiou, A.; Djalante, R.; Ebi, K. The human imperative of stabilizing global climate change at 1.5 °C. Science 2019 , 365 , eaaw6974. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Small, C.; Nicholls, R.J. A global analysis of human settlement in coastal zones. J. Coast. Res. 2003 , 584–599. [ Google Scholar ]
• Wang, W.; Liu, H.; Li, Y.; Su, J. Development and management of land reclamation in China. Ocean Coast. Manag. 2014 , 102 , 415–425. [ Google Scholar ] [ CrossRef ]
• Zimmermann, E.; Bracalenti, L.; Piacentini, R.; Inostroza, L. Urban flood risk reduction by increasing green areas for adaptation to climate change. Procedia Eng. 2016 , 161 , 2241–2246. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Xu, L.; Wang, X.; Liu, J.; He, Y.; Tang, J.; Nguyen, M.; Cui, S. Identifying the trade-offs between climate change mitigation and adaptation in urban land use planning: An empirical study in a coastal city. Environ. Int. 2019 , 133 , 105162. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Bilskie, M.; Hagen, S.; Medeiros, S.; Passeri, D. Dynamics of sea level rise and coastal flooding on a changing landscape. Geophys. Res. Lett. 2014 , 41 , 927–934. [ Google Scholar ] [ CrossRef ]
• Lentz, E.E.; Thieler, E.R.; Plant, N.G.; Stippa, S.R.; Horton, R.M.; Gesch, D.B. Evaluation of dynamic coastal response to sea-level rise modifies inundation likelihood. Nat. Clim. Chang. 2016 , 6 , 696–700. [ Google Scholar ] [ CrossRef ]
• Viguié, V.; Hallegatte, S. Trade-offs and synergies in urban climate policies. Nat. Clim. Chang. 2012 , 2 , 334–337. [ Google Scholar ] [ CrossRef ]
• Brody, S.D.; Highfield, W.E. Open space protection and flood mitigation: A national study. Land Use Policy 2013 , 32 , 89–95. [ Google Scholar ] [ CrossRef ]
• Brody, S.D.; Zahran, S.; Highfield, W.E.; Grover, H.; Vedlitz, A. Identifying the impact of the built environment on flood damage in Texas. Disasters 2008 , 32 , 1–18. [ Google Scholar ] [ CrossRef ]
• Arkema, K.K.; Guannel, G.; Verutes, G.; Wood, S.A.; Guerry, A.; Ruckelshaus, M.; Kareiva, P.; Lacayo, M.; Silver, J.M. Coastal habitats shield people and property from sea-level rise and storms. Nat. Clim. Chang. 2013 , 3 , 913–918. [ Google Scholar ] [ CrossRef ]
• Beck, M.W.; Losada, I.J.; Menéndez, P.; Reguero, B.G.; Díaz-Simal, P.; Fernández, F. The global flood protection savings provided by coral reefs. Nat. Commun. 2018 , 9 , 1–9. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Del Valle, A.; Eriksson, M.; Ishizawa, O.A.; Miranda, J.J. Mangroves protect coastal economic activity from hurricanes. Proc. Natl. Acad. Sci. USA 2020 , 117 , 265–270. [ Google Scholar ] [ CrossRef ]
• Sun, F.; Carson, R.T. Coastal wetlands reduce property damage during tropical cyclones. Proc. Natl. Acad. Sci. USA 2020 , 117 , 5719–5725. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Xiamen Evening News. The Total Area of Xiamen’s Mangrove Forest Is about 2 Million Square Meters. Available online: http://news.xmnn.cn/xmnn/2020/08/15/100767684.shtml (accessed on 7 March 2021).
• Lin, P.; Zhang, Y.; Yang, Z. Protection and restoration of mangroves along the coast of Xiamen. J. Xiamen Univ. (Nat. Sci.) 2005 , 44 , 1–6. [ Google Scholar ]
• Morris, R.L.; Boxshall, A.; Swearer, S.E. Climate-resilient coasts require diverse defence solutions. Nat. Clim. Chang. 2020 , 10 , 485–487. [ Google Scholar ] [ CrossRef ]

Click here to enlarge figure

Share and Cite

Xu, L.; Ding, S.; Nitivattananon, V.; Tang, J. Long-Term Dynamic of Land Reclamation and Its Impact on Coastal Flooding: A Case Study in Xiamen, China. Land 2021 , 10 , 866. https://doi.org/10.3390/land10080866

Xu L, Ding S, Nitivattananon V, Tang J. Long-Term Dynamic of Land Reclamation and Its Impact on Coastal Flooding: A Case Study in Xiamen, China. Land . 2021; 10(8):866. https://doi.org/10.3390/land10080866

Xu, Lilai, Shengping Ding, Vilas Nitivattananon, and Jianxiong Tang. 2021. "Long-Term Dynamic of Land Reclamation and Its Impact on Coastal Flooding: A Case Study in Xiamen, China" Land 10, no. 8: 866. https://doi.org/10.3390/land10080866

Article Metrics

Article access statistics, further information, mdpi initiatives, follow mdpi.

Subscribe to receive issue release notifications and newsletters from MDPI journals

3.16 Case Study - Flooding in Somerset (2013-2014)

For a period of three months from December 2013 to February 2014, the Somerset Levels hit the national (United Kingdom) headlines as the area suffered from extensive flooding. At the height of the winter floods, 65 km2 of land on the Levels were under water. This was caused by human and physical factors. The floods were the most severe ever known in this area.

No one was prepared for the extent of damage brought by the floodwater. Several villages and farms were flooded and hundreds of people had to be evacuated. The risk of flooding is likely to increase in the future due to climate change. The government will need to invest in flood defences in order to protect areas at risk.

Flooding on the Somerset Levels - The News

Flooding on the Somerset Levels - Background Information

In December 2013, an unusually high amount of rainfall began to fall on the Somerset Levels and this continued into February 2014. With so much water, the ground became saturated, forcing both the river Parrett and the river Tone to flood. 

The physical characteristics of the Somerset Levels and Moors mean that flooding is a natural occurrence there. It is an area of low-lying farmland and wetlands between the Mendip and Blackdown Hills in central Somerset. This area forms the floodplain surrounding the river Parrett. 

Thousands of years ago the area was covered by the sea. It has since been drained to allow for agriculture, several villages and wetland conservation. It has become an area of social, economic and environmental importance. It covers an area of 650 km2 but has a low population density (the number of people per km2 ). The area may have had a natural vulnerability to floods but no one was prepared for the scale of the floods or the impacts that followed

What caused the flooding on the Somerset Levels?

A river flood is when the river bursts its banks and spills onto the surrounding floodplain. A floodplain is an area of low-lying ground next to a river, formed mainly of river sediments. A flood can last just a few days or several weeks. A flood event is often caused by a combination of physical and human factors.

Physical causes

Prolonged rainfall: In January 2014 in southern England, rainfall totalled 183.8 mm, which is approximately 200% higher than average for that month (Figure 2). That was the wettest since records began in 1910. 

Saturated ground: The long period of rainfall caused the ground to become saturated so that it could not hold any more water. 

Low-lying land: Much of the area lies at, or just a few metres above, sea level, putting it at risk of flooding. 

High tides and storm surges from the Bristol Channel: These prevent the floodwater from being taken to the sea, forcing it to back up the rivers.

Human Causes

Lack of dredging: Over the years the rivers had become clogged with sediment. The Environment Agency had decided to stop dredging the rivers some time earlier. Dredging increases the ability of a river to carry more water. 

Change in farming practices: Much of the land has been converted from grassland to grow maize. This more intensive use of the land means it is less able to retain water, causing it to run over the surface rather than being absorbed.

Impacts of the Somerset floods 

The widespread flooding on the Somerset Levels made the national headlines. Many people visited the affected areas to see the famous floods. Such people became known as ‘flood tourists’. Many of the people living on the Levels had experienced some form of flooding in the past but no one was quite prepared for the scale of these floods. Thankfully no one died, but many people suffered flood damage to their homes, possessions and farmland (Figure 3). 

Many people were evacuated and had to seek temporary accommodation elsewhere. More than 600 homes and 6880 hectares of farmland were flooded. Entire villages were cut off after roads became unusable. In the village of Muchelney, residents could only leave the island by a boat which left every two hours (Figure 4).

Isolated communities provided an opportunity for thieves. In January, 900 litres of fuel was stolen from a pumping station in Westonzoyland. By early February, there were reports of stolen heating oil and quad bikes from homes of flood victims. Many of the main roads were closed, such as the A361 which links Taunton and Street. Trains on the Bristol line between Bridgwater and Taunton were also disrupted. The economic costs soon started to rise. Fuel for emergency pumps used to reduce water levels cost £200 000 per week. Local businesses reported over £1 million in lost business. According to ‘Visit Somerset’ the floods on the Somerset Levels cost the county’s tourism industry £200 million. 

Farmers struggled to deal with flooded fields, ruined crops and the costs of moving livestock away from the affected areas. After nearly three months under millions of tonnes of water, much of the soil was damaged. It may take up to two years to restore the soil so that crops can be grown. Flood-hit home owners are likely to see their insurance costs increase in the future.

Management and Response

The response to the floods was rapid and well organised, as expected for an economically developed country (Figure 5). The Met Office issued an amber warning for heavy rain in South West England. They informed the public to be prepared for significant flooding. Many residents used sandbags to protect their homes and moved valuable items upstairs. One man even built a giant wall out of clay and soil around his house in Moorland to protect it from the floodwaters.

The fire brigade visited hundreds of properties, and rescue boats were used to help stranded people. In early February, rescue crews encouraged the residents of Moorland to evacuate. Owners of around 80 homes agreed but about 30 other residents chose to remain (Figure 6). Extra police patrols were brought in to respond to increased crime. By the end of January, the army had been sent in with specialist equipment. They delivered food and gave out sandbags. By 6 February they were joined by 40 Royal Marines. Sixty-five pumps were used to drain 65 million m3 of floodwater. 

There was a lot of local support for those affected by the floods, led by the organisation FLAG (Flooding on the Levels Action Group). Volunteers organised fundraising activities and collected and distributed supplies of food. They also used social media via Facebook and Twitter to communicate news.

The longer-term response focused on flood management to prevent a future flood of this scale. This took the form of ‘The Somerset Levels and Moors Flood Action Plan’. It included measures such as dredging, a tidal barrage, and extra permanent pumping sites, with a total cost of £100 million. A sum of £10 million was provided by the Conservative Government, a further £10 million came from the Department for Transport, and the Department for Communities and Local Government gave £500 000. It formed part of a 20-year plan for the Levels. It had the backing of Prime Minister David Cameron who stated: ‘We cannot let this happen again’. 

Future Considerations 

In November 2014, the Environment Agency (EA) kept its promise and completed the 8 km dredging of the rivers Parrett and Tone, costing £6 million. This will be a huge help in the protection of homes and farmland. Some people have argued that dredging alone is not the answer and it should be used alongside other forms of flood defence, such as flood relief channels. Can the government afford to spend so much money in a rural area with a low population? 

Climate change may mean that this area will receive more heavy rain in the future. The Met Office has predicted that sea levels around the UK will rise by 11–16 cm by 2030. It may be that spending money on hard engineering flood defences is not the best option for this area. The government may save money in the long term by moving people to higher land, and to pay them money for their homes and farms. However, this is unlikely to be a popular option. 

Conclusion 

The recent floods demonstrate how more people have put themselves at risk of flooding by living on this low-lying floodplain. Farming and settlement increased because people thought that flooding in the area was under control. This was clearly not the case and it is therefore not surprising that the local people felt so let down. There were many impacts of this flood, but they could have been far worse if it had not been for the effective and rapid response that followed.  

Further Information

Click here to return to the Home page.

Future Strategies

State Case Studies

Federal Review

Management Goals

• Holistic Approach to Coastal FRM

CONTENTS ≡

CONTENTS ✕

Coastal Management Program

Shoreline regulations, floodplain management, wetland management, building codes, community planning, stormwater and runoff management, erosion management, climate adaptation initiatives, state management capacity, alternatives to structural mitigation, long-term planning, balance of mitigation and disaster recovery, holistic management approach, florida coastal flood risk management case study.

Policies and Programs

The Office of Resilience and Coastal Protection , like its counterparts in other states, was developed under the purview of the federal Coastal Zone Management Act . The program gained NOAA approval in 1981 following the passage of the Florida Coastal Management Act. The coastal program operates through the Florida Coastal Office within the state Department of Environmental Protection (DEP) , which provides oversight over coastal management grants, the Coastal and Estuarine Land Conservation Program , and federal consistency reviews, among other activities. Based on the geography of Florida and the legal basis for the state program, the entirety of the state is defined as the coastal zone and falls within the authority of the state coastal management program.

As is the case with other state coastal management programs, the Office of Resilience and Coastal Protection conducts federal consistency reviews to ensure that federal actions that may affect the coastal zone are consistent with identified state enforceable policies. The intent behind this review process is to improve decision-making related to use of natural resources, vulnerability to coastal hazards, and state growth patterns, all of which have a potential nexus to coastal flood risk. Types of federal actions under review include federal agency activities, federal permitting or licensing activities, Outer Continental Shelf Activities , and federal assistance to state or local governments. Federal agency activities under the purview of federal consistency include proposals that physically alter coastal resources, plans that direct future agency actions, rulemaking that affects coastal zone use, and Outer-Continental Shelf leasing. Permitting consistency reviews are conducted as state permits such as Environmental Resource Permits or Joint Coastal Permits are processed.

In addition to federal consistency responsibilities, the Office of Resilience and Coastal Protection also oversees four types of areas of special management. Areas of Critical State Concern , recommended by the Florida Department of Economic Opportunity , are areas that would put natural resources at risk if uncontrolled development were to occur. Aquatic Preserves set aside certain state-owned submerged lands and associated coastal waters in areas that have exceptional biological, aesthetic, and scientific value, overseen by the Florida Coastal Office. The state’s water management districts implement Surface Water Improvement and Management areas, primarily focused on addressing water quality issues in critical water bodies. Beach and Inlet Management areas also exist where coastal erosion threatens natural resources.

Other Office of Resilience and Coastal Protection activities include land acquisition, a subgrant program, and outreach activities. Land acquisition by the management program is conducted through the NOAA Coastal and Estuarine Land Conservation Program, which is implemented and managed within the state through the Florida Forever Program . Land acquisition activities focus on fragile coastal upland and wetland resources including undeveloped and buffer areas. Subgrant programs include Coastal Partnership Initiative grants that provide funds to localities to support projects designed to improve community resilience, coastal resources stewardship, and access to coastal resources. The program has a number of outreach initiatives such as the Florida Assessment of Coastal Trends, a collection of indicators used to inform planning decisions, and the Performance Measurement System , a NOAA program designed to quantify the effectiveness of coastal zone management activities.

The Coastal Construction Control Line Program (CCCL) , which is one of three components of the state’s Beach and Shore Preservation Act , protects Florida’s sandy beaches and dunes from imprudent construction jeopardizing the beach/dune ecosystem. This program establishes an area of jurisdiction seaward of designated control lines in coastal areas in which specific siting and design criteria are enforced for construction activities. Construction standards seaward of the control line are typically more stringent in order to prevent beach and dune system destabilization and protect natural resource values including upland property protection during flood or storm events. The program is administered through a permit system, with CCCL permits issued based on the potential construction impacts to coastal environments, adjacent properties, and wildlife, including specific requirements for shoreline armoring activities.

Rules and requirements related to the CCCL are found in chapter 62B of the Florida Administrative Code . General prohibitions based on program standards include coastal construction without necessary permits, coastal construction projects that will result in adverse impacts with consideration of proposed mitigation plans, and construction projects that will interfere with public use of areas seaward of the high-water line, except when deemed necessary. Approval or denial of a permit application is based upon a review of the facts and circumstances on the potential impacts on the beach dune/system, adjacent properties, native salt-resistant vegetation and marine turtles, and interference with public beach access. Given this department policy, CCCL permits are approved only when a construction project is shown to have a net positive benefit on surrounding coastal systems.

Criteria for permit approval include a number of measures with a nexus to coastal flood risk. The use of green or flexible coastal infrastructure is required where practicable. Structures that may alter coastal sediment movement are prohibited unless a net benefit to coastal systems is demonstrated or mitigation of adverse coastal impacts is provided. Permits for coastal armoring are also restricted except as a last resort for certain eligible structures, and armoring is only permitted after consideration of alternatives such as dune enhancement, beach restoration, and structure relocation. Sea level rise must also be considered during the review of coastal armoring applications. Any existing structures that have caused adverse impacts due to interference with coastal sediments must be redesigned or relocated during any reconstruction projects, and such structures may also be ordered removed if threats exist to human life, health, or welfare. Coastal construction projects determined to have an adverse impact must employ a program to monitor any impacts to coastal systems, and any unavoidable adverse impacts must be offset through a mitigation plan.

CCCL design and siting requirements also address a number of topics relevant to coastal flood risk. In order to obtain a permit for coastal construction, projects must be sited and designed in a way that minimizes adverse impacts to the coastal system. Requirements also limit the maximum level of protection provided by coastal armoring depending on structure type, extending up to a 50-year return interval storm for public safety facilities, evacuation routes, and historic sites. Coastal armoring structures must be placed as close as possible to the protected structure and are prohibited from causing any adverse impacts on adjacent property. A number of specific engineering and construction requirements for coastal areas are also listed within the administrative code, including measures to ensure that seawalls, bulkheads, revetments, and toe scour protection are designed in a manner that does not increase upland flooding due to wave run up and overtopping. If fill is used in coastal areas it must be compatible with existing beach materials in order to preserve environmental functions,, and native salt-resistant vegetation is required for any beach or dune stabilization projects

Development in floodplain areas in Florida is managed at the local level using the standards of the National Flood Insurance Program . Community responsibilities in Florida involve recognition of flood hazards during community planning, adoption and enforcement of flood maps and flood damage prevention ordinances, and establishment of elevation standards for new and substantially improved residential and non-residential structures. Specific floodplain management practices and standards that go beyond federal and state requirements vary by locality. The State Floodplain Management Program in Florida, housed within the State Division of Emergency Management’s Bureau of Mitigation , operates as the State Coordinating Agency for the NFIP, working collaboratively with counties and municipalities in Florida to help administer local floodplain management regulations.

Beyond its coordinating responsibilities, the State Floodplain Management Program recently undertook a pilot program, CRS-CAV , to encourage enrollment in FEMA’s Community Rating System , which provides flood insurance premium discounts based on community implementation of additional or improved floodplain management practices. The pilot program includes seven performance measures: adoption of floodplain regulations aligned with state building codes, annual inspection of flood hazard areas and resolution of non-compliance, adoption of flood zone permit application forms, procedures, and checklists, use of FEMA’s Elevation Certificate Form with verification of accuracy, outreach to propane and air conditioning companies regarding compliant installations, development of substantial improvement or damage determination procedures, and online access to digitized flood insurance rate maps and elevation certificates.

Statewide floodplain management rules and regulations are largely consistent with NFIP standards. Floodway development is only permitted if a proposed project will not increase flood levels or adversely impact structures on other properties, demonstrated through a “No Rise” certification. Wave action is considered beyond coastal V zones in areas where revised FIRMs are able to delineate the extent of wave action between 1.5 and 3.0 feet, known as the coastal A zone or CAZ. CAZs are rated lower than V zones, but construction requirements in Florida are equivalent to V zones. A number of areas in Florida also exist within the federal Coastal Barrier Resource System , where NFIP insurance is unavailable for new or substantially improved structures. Coastal floodplains also intersect with areas subject to the Florida CCCL program. Where these areas overlap, the more restrictive code requirements and development standards apply.

In addition to statewide standards, local permits are necessary for any land-disturbing activities in flood zones including new construction, additions, substantial improvements, renovations, and substantial repairs. Mobile home placement, placement of temporary buildings, agricultural construction, transportation construction, use of fill, alteration of stream hydrology, and land subdivision also require local approval. Levee accreditation, elevation certificate requirements, restrictions on use of fill, and general elevation construction practices in flood hazard areas in Florida also remain consistent with standard NFIP practices.

Wetlands in Florida are managed through the state Environmental Resource Permit (ERP) program, part of the Department of Environmental Protection’s Submerged Lands and Environmental Resources Coordination initiative. The ERP program is implemented by the DEP and state Water Management Districts . While responsibilities can also be delegated to localities, this is currently not a widespread practice. Environmental Resource Permits regulate virtually all alterations to the natural landscape that exceed permitting thresholds, covering multiple topics such as wetland impacts, erosion, and stormwater with consideration of upland area impacts. The ERP program is operated in addition to any federal program that also regulates use of U.S. waters, allowing for joint permit applications with agencies such as the USACE . If activities occur within submerged lands owned by the state, a Sovereign Submerged Lands (SSL) permit is also required. SSL permits are granted through consent by rule, letter of consent, easement, or lease, and must be issued concurrently with a required ERP. Wetlands are delineated using a specific state methodology as opposed to the federal method, although the two produce generally similar results in practice. Delineations occur on a parcel by parcel basis following a request or as part of a permit application review.

A number of ERP criteria for evaluation form the basis of wetland management in Florida. Criteria apply to construction, alteration, operation, maintenance, abandonment, or removal of projects unless exempted by statute or rule, including dredging and filling, and are based on the programmatic goal of maintaining wetland ecological functions rather than acreage. Maintenance of water quality standards within wetlands is a key aspect of ERP criteria, as doing so preserves a number of wetland functions including flood storage. Several environmental conditions for issuance must be met in order to obtain a permit. Activities may not adversely impact the value of functions provided by wetlands to fish, wildlife, and other listed species. Applicants must also provide assurances that activities are not contrary to the public interest, weighing factors including changes in flood risk, and that activities will not not adversely affect the quality of receiving waters including wetlands, with additional standards for shellfish harvesting areas. Additional permit standards require that activities will not have secondary impacts to water resources or unacceptable cumulative impacts upon wetlands, the latter of which may be offset by mitigation activities.

Mitigation efforts, also based on wetland function rather than acreage, can only be employed after all practicable actions to reduce or eliminate adverse impacts of a project have been used. If deemed necessary, mitigation efforts must offset any adverse impacts to wetlands functions, determined through a state Uniform Mitigation Assessment Method , and projects may be denied permits if mitigation actions are unable to sufficiently offset these adverse impacts. A number of approaches can be used to mitigate adverse impacts, including restoration, enhancement, creation, or preservation of wetlands, adjacent surface waters, or upland areas that function as hydrologic contributing areas. As a best practice, mitigation efforts that create, restore, enhance, or preserve similar ecological communities to those impacted are encouraged, using historically present ecological conditions as a reference where possible. Mitigation activities that occur on-site are generally preferred, but mitigation may also be employed off-site or through purchase of credits from a mitigation bank as long as sufficient adverse impacts are offset.

The Florida Building Code shares many of the same fundamentals of flood resistant construction as the construction requirements of the NFIP. Building foundations must be capable of resisting flood loads, and walls and roofs must be structurally sound so as to minimize penetration by wind, rain, and debris. Lowest floors must be elevated to the level of the design flood event to prevent intrusion of floodwaters. Use of any enclosure below elevated floors is limited to parking, storage, and building access, and any such space must be constructed using flood damage resistant materials. All equipment and utilities must also be elevated or designed to withstand flood loads or otherwise be designed to be restored quickly. Several provisions of the Florida Building Code, which refers to the standards in ASCE 24: Flood Resistant Design and Construction , exceed the construction requirements of the NFIP, and communities may also enact higher standards than state requirements.

The most recent Florida Building Code contains several major updates to flood resistant construction requirements. One foot of freeboard above BFE is now required for dwellings in all flood zones. In addition to the foot of freeboard, critical facilities must be elevated or protected to a height of BFE plus two feet or the 500-year flood elevation. If an area is zoned as a coastal A zone, it is regulated in the same way as a V zone, with stemwalls permitted. Local scour and erosion hazards must also be considered in the design and construction of foundations in coastal A and V zones. Flood openings are required in all walls and breakaway walls, and an exterior door is required at the opening of any stairways enclosed by breakaway walls. Restrictions on dry floodproofing of mixed use buildings have also been updated according to ASCE commentary. The updated code also includes a modified section addressing Florida’s CCCL programs requirements, which are now more closely aligned with coastal V zone requirements in an effort to minimize case-by-case determinations of which set of regulations apply as the more restrictive.

Regional Planning Councils conduct planning at the regional level in Florida. Communities must also develop comprehensive plans to account for future economic, social, physical, environmental, and fiscal development. Comprehensive plans must contain a number of elements including future land-use, transportation, water quality, aquifer recharge, conservation of natural resources, open space, housing, intergovernmental coordination, and coastal management for designated coastal communities. To address concerns over sea level rise, coastal communities can also designate low lying coastal zones that experience frequent coastal flooding as adaptation action areas.

The coastal management element of a comprehensive plan must be designed to meet a number of objectives such as the maintenance and enhancement of the coastal zone environment, balance of utilization and preservation of coastal resources, limit of public expenditures that subsidize development in high-hazard areas, and protection from the effects of natural disasters. State statutes establish a number of components required of coastal management planning elements to meet these objectives, including several with a nexus to coastal flood risk. Future land use plans must be evaluated in terms of environmental and socioeconomic impacts to coastal resources, and plans must be developed to mitigate adverse impacts. Principles for natural disaster hazard mitigation must also be developed, as well as principles for protection of existing beach and dune systems. Development and redevelopment principles of coastal management plans must also contain solutions that reduce flood risk, whether it be from high-tide events, storm surge, flash floods, stormwater runoff, or sea level rise.

Stormwater management practices, implemented through the state DEP and WMDs, are also under the purview of Florida’s comprehensive Environmental Resource Permit program. As with other types of activities affecting Florida’s landscapes and surface waters, the construction, alteration, operation, maintenance, abandonment, or removal of a stormwater management system must meet permitting criteria if permitting thresholds are exceeded, unless specifically exempted. Due to the comprehensive nature of the ERP program, stormwater management systems are evaluated in terms of adverse effects to both surface water quality and quantity, and as a general rule activities must not be harmful to water resources or inconsistent with overall objectives of the DEP or relevant Water Management District .

Water quantity performance standards for ERPs are designed to prevent adverse impacts due to changes in peak stormwater discharge rate, volume, and pollutant loading. To receive a permit, applicants must provide information to ensure that activities will not cause adverse flooding of any kind. Projects must not alter floodways, floodplains, levels of flood flows, or velocities of adjacent streams in a way that adversely impacts the off-site flood storage and conveyance capabilities of a water resource. Activities must also avoid any adverse impacts due to low flow conditions or disruption of base flow levels. Specific design and performance standards relevant to stormwater quantity are developed and published by each Water Management District. In terms of water quality, activities must comply with Florida’s state water quality standards and obtain permits through the National Pollutant Discharge Elimination System where relevant.

Erosion management and sediment control are also components of Florida’s Environmental Resource Permit program. Applicants must provide a plan for minimizing erosion and controlling sediment discharge as part of an ERP application. Plans are site specific, and must take into account the location, installation, and maintenance of best management practices at construction sites. Larger project permits also require development and implementation of a Stormwater Pollution Prevention Plan as part of Florida’s National Pollutant Discharge Elimination System Stormwater Construction Generic Permit . Though these permit programs are generally focused on preventing stormwater pollution during construction, permit criteria also have a nexus to flood impacts.

As a rule best management practices must be used to retain sediment on-site during construction, and practices must also assure that any sediment discharges do not cause or contribute to a violation of state water quality standards. Additional erosion control efforts are required if a project may lead to adverse impacts to wetlands or cause off-site flooding. The state CCCL program additionally addresses erosion of coastal sediment through coastal construction requirements. Principles to be considered as part of an erosion and sediment control plan include consideration of landscape topography and drainage patterns, maintenance of low runoff velocities, and stabilization of areas after final grade has been obtained. It is recommended that erosion control activities consist of both vegetative and structural measures along with other management techniques to minimize movement of sediment.

Adaptation measures related to climate change, particularly with respect to sea level rise, are present in a number of state policies and programs such as the coastal construction line, adaptation action areas, and coastal management element of comprehensive planning. Apart from measures incorporated into other programs, Florida also has state level initiatives to address climate change. A 2007 executive order from the governor established the Governor’s Action Team on Energy and Climate Change and required the development of Florida’s Energy and Climate Action Plan . The action plan identifies a number of adaptation strategies relating to topics such as scientific data and analysis, comprehensive planning, protection of ecosystems and biodiversity, water resources management, and community protection. The action plan also outlines a planning framework with specific goals related to flood protection and strategies for implementation. In 2011, the state developed the Community Resilience Initiative , with NOAA funding provided to the Florida Department of Economic Opportunity through the Department of Environmental Protection. This 5 year Initiative ended in December 2017 and DEP is currently managing the next 4 years of NOAA grant funding, known as the Adaptation Action Initiative. The new Initiative will provide assistance to coastal communities to implement planning strategies that address long-term coastal flood risk resulting from sea level rise that were developed during the previous five years. These innovative planning strategies will be implemented in two communities annually in critical coastal areas

A number of local and regional climate adaptation initiatives have also been developed in coastal areas throughout Florida. One major regional initiative is the Southeast Florida Regional Climate Compact , a collaborative effort among four counties in southeast Florida to coordinate mitigation and adaptation activities. The compact works to respond to state legislation related to climate adaptation and publishes planning guidance documents for use in coastal communities. One such guidance document is the Southeast Florida Regional Climate Action Plan , which outlines a framework for addressing impacts due to a changing climate, including actionable recommendations in areas such as sustainable community planning, water supply and infrastructure, natural systems, agriculture, energy, risk and emergency management, and public policy. The compact has also produced an implementation guide to accompany the climate action plan and has published regional unified sea level rise projections for planning purposes.

Elements of Policy Goals/Management Principles

• The entirety of the state of Florida falls under the formal definition of the coastal zone, providing the state coastal management program with the authority necessary to fully address coastal issues even if such issues stem from inland areas.
• The federal consistency review process gives the Office of Resilience and Coastal Protection influence over federal actions in the coastal zone. The Florida program has a broad range of enforceable policies that federal actions must be consistent with, increasing the scope of the consistency review process.
• The state coastal management program’s Coastal Partner Initiative grants bolster flood risk management capacity throughout the state by funding projects to improve coastal community resilience.
• Wetland delineation for wetland management purposes is performed using a specific state methodology that differs from the federal method. The methods produce similar results, but the presence of a state method provides a precedent for changes in delineation methodology depending on state priorities.
• State Water Management Districts publish specific design and performance standards related to stormwater quantity, improving sate capability to address regional stormwater issues.
• The Office of Resilience and Coastal Protection conducts land acquisitions through the Florida Forever Program and NOAA Coastal and Estuarine Land Conservation Program, with acquisitions focusing on undeveloped and buffer areas within coastal uplands and wetlands.
• The Coastal Construction Control Line Program establishes specific siting and design requirements for designated coastal areas. Permit approval for the program requires the use of green coastal infrastructure where practicable, and coastal armoring is only permitted after alternative measures have been evaluated.
• Wetland mitigation within Florida is based on ecological function as opposed to acreage, with impacts determined through a state Uniform Mitigation Assessment. Mitigation efforts that create, restore, enhance, or preserve wetland functions are encouraged.
• Erosion management guidance recommends the use of vegetative measures in coastal areas to minimize movement of sediment.
• Sea-level rise must be considered during review of coastal armoring applications as part of Coastal Construction Control Line permit approval.
• Coastal Construction Control Line design requirements for coastal armoring projects include levels of protection for different structure types based on coastal storm return intervals, extending to 50-year return interval storms for public safety facilities, evacuation routes, and historic sites.
• Dwellings in all flood zones must be elevated one foot above the base flood elevation, and critical facilities must be elevated to two feet above the base flood elevation or to the 500-year flood elevation.
• Low lying areas in the coastal zone that experience frequent flooding can be designated as adaptation action areas. The purpose of these areas as stated in the state administrative code is to address future issues related to sea level rise.
• The development and redevelopment principles within the coastal management element of a community’s comprehensive plan must address future flood risk from sources such as high-tide events and sea-level rise.
• Florida’s Energy and Climate Action Plan was formed following a 2007 executive order and contains a planning framework with specific goals related to flood protection as well as strategies for implementation.
• The state Community Resilience Initiative assists coastal communities with the development of planning strategies for future flood risk due to sea-level rise, leveraging resources from the Florida Department of Economic Opportunity, Department of Environmental Protections, and Division of Emergency Management.
• Regional climate adaptation initiatives such as the Southeast Florida Regional Climate Compact coordinate mitigation and adaptation activities. The compact has published a climate action plan, an implementation guide, and regional sea-level rise projections for planning purposes.
• As part of the Coastal Construction Control Line Program, any unavoidable adverse impacts of coastal construction projects must be offset through a mitigation plan, including a program to monitor impacts to coastal systems.
• The CRS-CAV program, a pilot program under the State Floodplain Management Program, seeks to increase enrollment in FEMA’s Community Rating System, with a number of performance measures designed to increase the effectiveness of mitigation practices.
• Areas rated as coastal A zones on FEMA flood maps have the same construction requirements as V zones within Florida, providing a higher level of protection for at-risk coastal areas.
• The coastal management element of a community’s comprehensive plan must address the limitation of public expenditures that subsidize development in high-hazard areas, acknowledging the benefits of responsible investment in coastal areas.
• The Office of Resilience and Coastal Protection’s enforceable policies used for federal consistency review encompass the use of natural resources, vulnerability to coastal hazards, and state growth patterns, addressing coastal issues from multiple perspectives.
• Areas of special management within the Office of Resilience and Coastal Protection are determined in part by risk to natural resources due to uncontrolled development or rapid urbanization, with input provided from the Florida Department of Economic Opportunity.
• The Coastal Construction Control Line Program is based on the state Department of Environmental Protection policy of regulating coastal construction to prevent degradation and promote restoration of coastal ecosystems, formally addressing the connection between development and ecological function. Program permits are also evaluated on the more broad concept of net benefits to coastal systems as opposed to more narrow performance measures.
• The comprehensive nature of Florida’s Environmental Resource Permit program as well as the programs focus on ecological functions encourages applicants to consider potential project impacts from multiple perspectives, such as preserving water quality within wetlands to maintain flood storage functionality.
• Under the Environmental Resource Permit program, stormwater management systems are evaluated in terms of both water quality and quantity, with performance standards that extend beyond pollutant loading to ensure that activities do not lead to adverse impacts on stormwater discharge rate or volume.
• Comprehensive plans for communities must contain an element related to intergovernmental coordination, and designated coastal communities must also develop a coastal management element, encouraging management of coastal issues across multiple government entities during the planning process.
• Climate adaptation measures are dispersed throughout several state programs addressing coastal issues such as the Coastal Construction Control Line, adaptation action areas, and coastal management element of comprehensive planning, building adaptation capacity into existing programs without reliance on new initiatives.

View the other State Coastal Flood Risk Management Case Studies:

• 0 Shopping Cart

Medmerry Case Study

Coastal Realignment

Medmerry Case Study Coastal Realignment

Medmerry, West Sussex, on the south coast of England, is Europe’s largest coastal realignment scheme.

Medmerry Coastal Realignment

Why was the Medmerry coastal realignment scheme needed?

Medmerry had long faced problems with flooding from the sea, with regular breaches of the shingle bank, most recently in 2008, when over £5m of damage was caused. Several hundred thousand pounds were spent repairing and maintaining the shingle bank every year. Without annual maintenance, 348 properties in Selsey, a water treatment plant and the main road between Chichester and Selsey would be flooded, along with many holiday homes and rental cottages. The last time the sea breached the shingle bank in 2008, it caused damage totalling £5 million.

What is the Medmerry coastal realignment scheme?

Medmerry is the largest managed realignment of the open coast in Europe, and the first in the UK, on the stretch of the southeast coast most threatened by coastal flooding. The scheme has created an intertidal habitat, replacing vital areas lost in the Solent, allowing new defences to be built and protecting thousands more properties along the coastline.

The scheme is recognised locally, nationally and internationally as an exemplar scheme and is one of the most sustainable projects the Environment Agency has delivered.

Aerial view of the Medmerry Coastal Realignment Scheme – Image: Environment Agency

Work began on the Medmerry Coastal Realignment Scheme in 2011 following a public consultation. It was completed in 2014. The project was achieved by:

• Constructing a new 7km embankment using clay from within the area. The embankment created a new intertidal zone , protecting properties behind it from coastal flooding.
• A channel was built behind the embankment to collect draining water. This water is taken back into the intertidal zone via four outfall structures.
• Sixty thousand tonnes of rock from Norway was used to build up rock armour on the seaward edges of the embankment, linking to the remaining ridge.
• Once the rock amour and embankment were complete, a 110-metre breach was made in the shingle bank on the beach , allowing the sea to flood the land and creating the new intertidal zone.

What are the positive effects of the Medmerry Coastal Realignment Scheme?

What are the social benefits of the Medmerry Coastal Realignment Scheme?

• Selsey now has the best protection from coastal flooding, with only a 1 in 1000 chance of coastal flooding. 348 properties and sewage works are now protected to a standard of 1 in 100 years (previously just 1 in 1 year). The scheme avoided a possible breach during severe winter storms in 2013.
• The area now has ten kilometres of footpaths, seven kilometres of bike paths, and five kilometres of bridleways compared to the previous two small footpaths before the scheme was developed.

What are the economic benefits of the Medmerry Coastal Realignment Scheme?

• Caravan parks and Selsey’s main road route are now protected to a standard of 1 in 100 years (previously just 1 in 1 year).
• The local economy has received a boost from an increase in green tourism , and the caravan parks have been able to extend their season, generating income and jobs. Two new car parks and four viewing points give easy access.
• Vegetation on the salt marsh supports extensive cattle farming, producing expensive salt-marsh beef.

What are the environmental benefits of the Medmerry Coastal Realignment Scheme?

• The site contains 300 hectares of habitat of principal importance under the UK Biodiversity Action Plan, including mudflats, reed beds, saline lagoons and grassland. This includes 183 hectares of newly created intertidal habitat important to wildlife on an international level. It is crucial in compensating for losses due to development around The Solent, allowing the region to meet its European directive targets. Birds and other new wildlife appeared at the site long before completion.
• The area is now a huge nature reserve managed by the RSPB.

What issues and conflicts resulted from the Medmerry coastal realignment scheme?

What are the social issues of the Medmerry Coastal Realignment Scheme?

• Some residents feel that the Environmental Agency should have explored other options, such as an offshore reef or continued beach realignment, and not have given up on the land so easily.
• Some opponents from outside the area resented a significant sum of money being spent on a scheme in such a sparsely populated area.

What are the economic issues of the Medmerry Coastal Realignment Scheme?

• The project was expensive at £28 million compared to £0.2 million a year to maintain the shingle wall. Though with rising sea levels, this can be challenged quite easily.
• Good agricultural land was abandoned, leading to the loss of three farms growing winter wheat and oilseed rape.

What are the environmental issues of the Medmerry Coastal Realignment Scheme?

• Despite extensive planning , the habitats of existing species were disturbed.

Premium Resources

Please support internet geography.

If you've found the resources on this page useful please consider making a secure donation via PayPal to support the development of the site. The site is self-funded and your support is really appreciated.

Related Topics

Use the images below to explore related GeoTopics.

Topic Home

Next topic page, share this:.

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)
• Click to share on Pinterest (Opens in new window)
• Click to email a link to a friend (Opens in new window)
• Click to share on WhatsApp (Opens in new window)
• Click to print (Opens in new window)

If you've found the resources on this site useful please consider making a secure donation via PayPal to support the development of the site. The site is self-funded and your support is really appreciated.

Search Internet Geography

Latest Blog Entries

Pin It on Pinterest

• Click to share
• Print Friendly

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

• View all journals
• Explore content
• About the journal
• Publish with us
• Sign up for alerts
• Open access
• Published: 28 August 2024

Global insights on flood risk mitigation in arid regions using geomorphological and geophysical modeling from a local case study

• Adel Kotb   ORCID: orcid.org/0000-0002-8188-3188 1 ,
• Ayman I. Taha   ORCID: orcid.org/0000-0003-4526-1784 2 ,
• Ahmed A. Elnazer   ORCID: orcid.org/0000-0002-7338-0935 3 &
• Alhussein Adham Basheer   ORCID: orcid.org/0000-0001-5283-9201 1  

Scientific Reports volume  14 , Article number:  19975 ( 2024 ) Cite this article

Metrics details

• Environmental sciences
• Natural hazards

This research provides a comprehensive examination of flood risk mitigation in Saudi Arabia, with a focus on Wadi Al-Laith. It highlights the critical importance of addressing flood risks in arid regions, given their profound impact on communities, infrastructure, and the economy. Analysis of morphometric parameters ((drainage density (Dd), stream frequency (Fs), drainage intensity (Di), and infiltration number (If)) reveals a complex hydrological landscape, indicating elevated flood risk. due to low drainage density, low stream frequency, high bifurcation ratio, and low infiltration number. Effective mitigation strategies are imperative to protect both communities and infrastructure in Wadi Al-Laith. Geophysical investigations, using specialized software, improve the quality of the dataset by addressing irregularities in field data. A multi-layer geoelectric model, derived from vertical electrical sounding (VES) and time domain electromagnetic (TDEM) surveys, provides precise information about the geoelectric strata parameters such as electrical resistivity, layer thicknesses, and depths in the study area. This identifies a well-saturated sedimentary layer and a cracked rocky layer containing water content. The second region, proposed for a new dam, scores significantly higher at 56% in suitability compared to the first region’s 44%. The study advocates for the construction of a supporting dam in the second region with a height between 230 and 280 m and 800 m in length. This new dam can play a crucial role in mitigating flash flood risks, considering various design parameters. This research contributes to flood risk management in Saudi Arabia by offering innovative dam site selection approaches. It provides insights for policymakers, researchers, and practitioners involved in flood risk reduction, water resource management, and sustainable development in arid regions globally.

Similar content being viewed by others

Pre-failure operational anomalies of the Kakhovka Dam revealed by satellite data

Current and projected flood exposure for Alaska coastal communities

Assessing flash flood erosion following storm Daniel in Libya

Introduction.

Floods have long been recognized as one of the most devastating natural disasters, posing significant threats to communities worldwide 1 . In the Kingdom of Saudi Arabia (KSA), a region characterized by arid landscapes and sporadic rainfall, floods can have catastrophic consequences 2 . This paper aims to address the multifaceted issue of flood risks and their profound impact on the communities of KSA 3 , 4 . Furthermore, it underscores the critical importance of mitigating these risks through the judicious selection of dam sites, emphasizing the utilization of geophysical and geomorphological modeling techniques 5 .

Floods in KSA, while infrequent, are nonetheless devastating when they occur due to the arid nature of the region 6 . These events can lead to loss of life, damage to infrastructure, disruption of livelihoods, and economic losses 7 . Understanding the dynamics of flood risks is essential for safeguarding the well-being of KSA’s communities and ensuring the sustainable development of the region 8 . One pivotal approach to mitigating the impact of floods in KSA is through the strategic placement of dams 9 . These structures play a vital role in flood control, water resource management, and supporting agricultural activities 10 . Therefore, the selection of appropriate dam sites is paramount to the overall flood risk reduction strategy.

In this context, this paper centers its focus on the application of geophysical and geomorphological modeling techniques, specifically within the unique setting of Wadi Al-Laith in KSA 11 . Wadi Al-Laith, characterized by its intricate topography and hydrological features, serves as an exemplary case study to demonstrate the efficacy of these innovative approaches in dam site selection (Fig.  1 ). To contextualize our research, we present a comprehensive review of previous studies related to flood risks and dam site selection within the KSA region 12 . These studies provide valuable insights into the historical context and existing methodologies employed in flood risk management. Acknowledging the limitations and challenges of existing approaches is fundamental to driving innovation in flood risk mitigation 13 . By critically evaluating past strategies, we can identify areas where geophysical and geomorphological modeling can enhance the accuracy and effectiveness of dam site selection 14 , 15 .

location map of the study area, ( a ) spatial location of Saudi Arabia (red) relative to the world (gray) created by map chart, https://www.mapchart.net/world.html , ( b ) spatial location of Wadi Laith (green) relative to Makkah governorate (yellow) in Saudi Arabia created by map chart, https://www.mapchart.net/asia.html , ( c ) spatial location of Wadi Laith [created using 26 .

This study’s objective is toestablish a holistic framework for enhancing flood risk mitigation strategies in the region and contribute to the ongoing discourse on flood risk management in KSA by exploring innovative approaches to dam site selection, particularly through a promising solution of the application of geophysical and geomorphological modeling 16 , 17 . It endeavors to offer recommendations that can advance the planning and selection of optimal locations for new dams, as well as evaluate the performance and efficiency of existing dams 18 , 19 . Ultimately, this research is dedicated to ensuring the protection of both the communities and critical infrastructure within the Kingdom of Saudi Arabia (KSA).

The primary aim of this paper is to comprehensively address the multifaceted issue of flood risks in the Kingdom of Saudi Arabia (KSA), highlighting the unique challenges posed by the region’s arid landscapes and sporadic rainfall. The paper emphasizes the catastrophic consequences floods can have on communities, infrastructure, livelihoods, and the economy within KSA, while also considering global implications. It underscores the critical importance of mitigating flood risks through the judicious selection of dam sites, advocating for the use of advanced geophysical and geomorphological modeling techniques to enhance decision-making processes. Recognizing the devastating impact of floods in KSA despite their infrequency, the study promotes the strategic placement of dams as essential for flood control, sustainable water resource management, and supporting agricultural activities.

The paper specifically focuses on Wadi Al-Laith as a case study to illustrate the efficacy of geophysical and geomorphological modeling techniques in dam site selection. This area’s intricate topography and hydrological features serve as an exemplary setting for showcasing innovative flood risk mitigation strategies that could potentially inform similar efforts globally. To provide a comprehensive context, the paper conducts a thorough review of previous studies related to flood risks and dam site selection within KSA, aiming to offer insights into historical contexts, existing methodologies, and challenges faced in flood risk management.

Moreover, the study aims to contribute to the global discourse on flood risk management by exploring innovative approaches to dam site selection that improve accuracy and effectiveness through advanced modeling techniques. By establishing a holistic framework for enhancing flood risk mitigation strategies in KSA, the paper seeks to provide recommendations that can advance the planning and selection of optimal dam locations and evaluate the performance of existing infrastructure. Ultimately, the research aims to protect communities and critical infrastructure in KSA and beyond, thereby improving global resilience to floods and promoting sustainable development practices worldwide.

Area under investigation

Wadi Al-Laith, located in the Kingdom of Saudi Arabia (KSA), is a distinctive geographical feature within the western region of the country 20 . It is characterized by a variety of unique geographical attributes that shape its landscape and hydrology (Fig.  1 ).

Wadi Al-Laith can be described as a wadi, which is a typically dry riverbed or valley that experiences sporadic and often intense flash floods during the rare rainfall events in the arid region of KSA 21 . The geographical features of Wadi Al-Laith include a meandering topography with a pronounced channel that can expand dramatically during flood events. The valley exhibits a narrow and winding path, surrounded by rocky terrain and outcrops, with the nearby presence of limestone formations 22 .

The region’s hydrology is further influenced by its proximity to the Red Sea and the surrounding mountain ranges, which can contribute to localized weather patterns and rainfall variability 23 . Due to its geological composition and topographical characteristics, Wadi Al-Laith becomes particularly susceptible to flash flooding, making it a pertinent area for studying flood risk mitigation.

Wadi Al-Laith has witnessed several historical flood events, which have had significant repercussions for the surrounding communities and infrastructure 14 , 24 . These flood events are typically associated with the sporadic but intense rainstorms that occasionally occur in the region. Over the years, these floods have resulted in loss of life, damage to property, disruption of transportation networks, and agricultural losses. These historical flood events serve as poignant reminders of the urgent need to develop effective flood risk mitigation strategies in the area 20 , 21 , 25 .

Wadi Al-Laith assumes paramount importance as a case study for flood risk mitigation and dam site selection for several compelling reasons. Firstly, the unique topographical and geological characteristics of the region, such as the presence of limestone formations and rocky outcrops, make it an ideal testing ground for assessing the effectiveness of mitigation measures, including the strategic placement of dams. Secondly, the historical flood events in Wadi Al-Laith provide valuable data and insights into the vulnerabilities and risks associated with flash floods in arid regions, which can inform the development of targeted mitigation strategies. Thirdly, the lessons learned from Wadi Al-Laith can be extrapolated to other wadis and flood-prone areas within KSA and similar arid regions globally, making it a crucial reference point for policymakers, researchers, and practitioners engaged in flood risk management.

Briefly, Wadi Al-Laith in KSA serves as an exemplary study area for comprehensively examining the geographical characteristics, historical flood events, and the imperative role it plays in advancing flood risk mitigation and dam site selection strategies. The insights gained from this case study have the potential to enhance the resilience of communities and infrastructure in arid regions, safeguarding them against the adverse impacts of flash floods.

Geological settings

Wadi Al Lith, situated in the western region of Saudi Arabia, boasts a distinctive geological landscape characterized by its diverse features (Fig.  2 ). The prevailing geological composition of this area primarily consists of sedimentary rocks, prominently marked by the presence of extensive limestone formations 27 . These limestone formations are integral components of the sedimentary sequence affiliated with the Arabian Platform, with origins traceable to the Cretaceous and Paleogene epochs 26 , 28 . Specifically, the study area within Wadi Al-Lith assumes the form of a valley stream typified by a thin sedimentary layer, the close proximity of hard rock strata to the surface, and rocky outcrops flanking the valley’s margins 29 . Notably, in select regions, sediment thickness within the valley gradually increases until it interfaces with the underlying hard rock formations.

Geological map of the area under investigation and its surroundings. [Created using 34 .

The geological framework of the Wadi Al-Lith catchment area comprises four primary rock units, as detailed by 27 , 30 .

Quaternary, encompassing sand, gravel, and silt deposits: yhis unit exhibits the predominant presence of eolian sand-dune formations and sheet sand and silt deposits, with sand deposits covering a substantial portion of the region.

Late- to post-tectonic granitic rocks: represented by various plutonic rock types, including diorite, tonalite, granodiorite, and monzogranite, alongside serpentinite to syenite formations.

Lith suite, Khasrah complex, diorite, and gabbro: constituting a suite of mafic to intermediate plutonic rocks.

Baish and Baha groups: comprising rocks such as basalt–dacite and biotite-hornblende-schist-amphibolite.

Additionally, Wadi Al-Lith encompasses volcanic rocks, notably basalt and andesite, remnants of ancient volcanic activity 2 . These volcanic formations are associated with the Red Sea rift system, a significant geological phenomenon that has profoundly influenced the region’s topographical characteristics 31 .

Structurally, the geology of the Wadi Al-Lith region is shaped by faulting and folding processes. Underlying the sedimentary rocks is the Arabian Shield, a Precambrian-age basement complex 31 . Characterized by its rugged and mountainous terrain, this geological foundation contributes significantly to the diverse topography evident in the area 27 , 32 .

The presence of a multitude of rock types and geological structures within Wadi Al-Lith holds significant implications for water resources and the occurrence of flash floods. Impermeable rock formations, such as limestone, can expedite surface runoff during intense precipitation events, augmenting the susceptibility to flash floods 27 , 32 . Consequently, a profound comprehension of the geological attributes of the region assumes paramount importance in facilitating effective water resource management and the implementation of appropriate mitigation measures aimed at mitigating the impact of flash floods 31 , 32 .

Methodology

The hydrogeological method in this study primarily involves using hydrological models to predict and map regions prone to flash floods. The geophysical methods employed include electrical resistivity sounding (VES) and time-domain electromagnetic (TDEM) methods to investigate subsurface layers. Combining hydrogeological and geophysical methods offers a comprehensive understanding of the factors influencing flash floods. Hydrological models derived from detailed morphometric and land cover analyses are augmented with subsurface information obtained from geophysical measurements. This integrated approach allows for more accurate predictions of flash flood-prone areas by considering both surface characteristics and subsurface conditions, ultimately enhancing flood risk mitigation strategies.

Hydrogeological method

In this study, hydrological models assume a pivotal role in the anticipation and mapping of flash flood-prone regions. The hydrological models used in this study are advanced and multifaceted, incorporating: (a) morphometric analysis which are utilizing parameters like drainage density, stream frequency, and rainage intensity, (b) topographic data derived from high-resolution topographic maps, (c) land cover data (integrated using the ASTER GDEM dataset), (d) subsurface information (enhanced with data from geophysical methods), and e) GIS Software: ArcGIS 10.4.1(for comprehensive data analysis).

These models work together to predict specific locales susceptible to flash floods, considering both surface and subsurface characteristics, to provide a holistic approach to flood risk mitigation in arid regions like the Kingdom of Saudi Arabia. These models find their genesis in morphometric analyses, which entail a comprehensive examination of the terrain's spatial characteristics and configurations. Topographic maps, boasting a horizontal posting resolution of approximately 30 m at the equatorial belt, serve as the primary data source for these morphometric inquiries. This level of detail facilitates an exhaustive comprehension of the landscape’s morphology and its ensuing influence on the hydrological patterns governing water flow.

To bolster the precision of the hydrological models, supplementary data regarding land cover is incorporated into the analytical framework. The research team leverages the ASTER Global Digital Elevation Model (GDEM) Version 3 33 , a dataset that furnishes a worldwide digital elevation model of terrestrial regions. This dataset boasts a spatial resolution of 1 arcsecond, equating to approximately 30 m on the ground. By integrating this land cover information into the hydrological models, the research endeavor accommodates pertinent factors such as vegetation types, soil compositions, and land use patterns, all of which exert substantial influences on the hydrological dynamics across the landscape.

Subsequently, hydrological models are brought into action to predict the specific locales susceptible to flash floods. These models simulate the water’s flow trajectory predicated on the amalgamation of topographic particulars and land cover attributes. In so doing, these models pinpoint areas where the confluence of terrain features and land cover characteristics renders them predisposed to the occurrence of flash floods. To further bolster the predictive capacity of these models, subsurface information procured through geophysical measurements is incorporated.

For the comprehensive analysis of data, including morphometric assessments, ArcGIS 10.4.1 software 34 is employed. This software platform facilitates data visualization, manipulation, and morphometric analyses, enabling a detailed exploration of the study area’s pertinent parameters. Key morphometric parameters essential to this study are presented in Table 1 , encompassing metrics such as drainage density (Dd), stream frequency (Fs), drainage intensity (Di), and infiltration number (If). These parameters, as outlined by 35 , 36 , form the cornerstone of the morphometric analyses undertaken in this investigation.

Geophysical methods

Geophysical methods, including electrical resistivity sounding (VES) and time-domain electromagnetic (TDEM) methods, are employed to investigate subsurface layers. The number of measurements were 157 VES and the same number of TDEM have been conducted in the same place to cover the whole area under investigation (Fig.  3 a). VES measures subsurface electrical resistivity at various points, yielding insights into subsurface composition and properties. In contrast, TDEM employs electromagnetic pulses to assess subsurface characteristics. These geophysical measurements inform the development of subsurface models.

( a ) Geographical distribution of VES and TDEM soundings’ site in the area under investigation [created using 26 , ( b ) example of VES no. 1 interpretation [extracted from 51 , ( c ) example of TDEM sounding no. 1 interpretation [extracted from 52 .

Geoelectrical method

Geoelectrical surveys, also known as the “DC method,” entail injecting direct electric current into the ground using surface-based current and voltage electrodes. The current’s direction is alternated to mitigate natural ground interference.

The vertical electrical sounding (VES) technique, utilizing continuous direct current (DC), is widely employed for groundwater exploration. It gauges values influenced by water content in rocks; higher values are characteristic of unsaturated rocks, while lower values indicate saturation, with salinity influencing measurements 37 .

The method of measuring ground electrical resistance relies primarily on Ohm's law, which states that the electric current flowing through a conductor is directly proportional to the voltage across it Eq. ( 1 ).

Ground electrical resistance is measured in accordance with Ohm’s law, where electric current is injected into the ground via two conductive electrodes (A and B) 38 , 39 Eqs. ( 2 ), ( 3 ).

The apparent electrical resistance (ρa) is determined by dividing the product of the potential difference (∆V) by the current strength (I) and multiplying it by a geometric constant (K), which varies based on the distance between the current and voltage electrodes. This process is conducted using the Schlumberger configuration, which allows for deeper measurements compared to other configurations 40 , 41 .

Simultaneously, the potential difference across two additional electrodes (M and N) within the ground is measured. Apparent electrical resistance (ρa) is calculated by dividing the product of potential difference (∆V) by current strength (I) and multiplying by a geometric constant (K), contingent on the electrode distance. The Schlumberger configuration is employed for deeper measurements Eqs. ( 2 ),( 3 ) 42 .

The geoelectrical survey in the study area was performed using the ARES II/1 43 device, manufactured in the Czech Republic, which has a high capacity to transmit a current of up to 5 A, a voltage of 2000 V, and a capacity of up to 850 W, enabling measurements to be taken until reaching the solid base rocks.

Time domain electromagnetic method (TDEM)

TDEM relies on electromagnetic induction principles, creating a varying magnetic field and measuring induced electrical currents in the subsurface.

A transmitter coil carrying a strong current generates a changing magnetic field penetrating the subsurface. This field induces secondary electrical currents (eddy currents) in conductive materials beneath the surface, resulting in secondary magnetic fields. Upon deactivating the transmitter coil, the eddy currents decay, and the associated magnetic fields diminish. A receiver coil captures changes in the magnetic field over time, known as the decay curve or decaying electromagnetic response, providing subsurface resistivity distribution insights 44 .

Key equations utilized in TDEM include Faraday’s law of electromagnetic induction, Maxwell’s equations Eq. ( 4 ), governing electromagnetic wave propagation, and Ampere’s law, accounting for electric currents and the displacement current.

where ( ∇  × B) is the curl of the magnetic field vector (B), (μ 0 ) is the permeability of free space, a fundamental constant, (J) is the electric current density, and (∂E/∂t) is the rate of change of the electric field vector (E) with respect to time. This equation relates magnetic fields to electric currents and the displacement current (the term involving ∂E/∂t), which accounts for the changing electric field inducing a magnetic field 45 , 46 .

The Cole–Cole model represents complex electrical conductivity in subsurface materials, incorporating parameters (σʹ, σʹʹ, and α) to account for frequency-dependent conductivity Eq. ( 5 ).

where the complex conductivity (σ*) and angular frequency (ω) and (j) is the imaginary unit (√(− 1)) 40 , 41 .

Inversion algorithms, based on forward modeling and optimization techniques, interpret TDEM data and construct subsurface resistivity models. The inversion process involves comparing predicted data with measured data and adjusting the resistivity model to minimize discrepancies. Iterations continue until a satisfactory match is achieved, yielding the best-fitting resistivity distribution. These methodologies enable the estimation of subsurface properties, valuable in groundwater exploration, mineral assessment, and geological formation characterization 47 . Figure  3 b, c illustrates an example of these interpretations.

By combining hydrological models derived from topographic and land cover data with the subsurface model obtained from geophysical measurements, a comprehensive understanding of the factors affecting the occurrence of flash floods can be achieved. This integrated approach allows for more accurate prediction of locations vulnerable to flash floods, as it takes into account surface characteristics and subsurface conditions.

In a clearer and more summarized sense, the hydrological models used in this study are derived from detailed morphometric studies based on topographic maps and land cover data. ASTER’s Global Digital Elevation Model (GDEM) version 3 is used to obtain land cover information. These models, along with subsurface information obtained through geophysical measurements and interpretation using VES and TDEM methods, contribute to predicting locations vulnerable to flash floods through a more comprehensive and accurate understanding of the contributing factors.

Hydrogeological modeling

In this study, a comprehensive analysis of the study area’s topography, hydrology, and precipitation patterns was conducted using various geospatial data sources and techniques. The digital elevation model (DEM) played a central role in extracting valuable insights.

The DEM was employed to delineate the drainage network within the study area, specifically focusing on the Wadi Lith watershed (Fig.  4 a). By assessing stream orders within this watershed, a significant observation emerged. It was noted that as the stream order increased, the number of associated stream segments decreased. Notably, the first-order stream (SU1) displayed the highest frequency, indicating that lower-order streams are more prevalent in the area. This observation underscores the heightened susceptibility of Wadi Lith to drainage-related hazards (Fig.  4 b).

( a ) Digital elevation map of the area under investigation, ( b ) drainage network map of the area under investigation. Created using 34 .

The DEM dataset yielded critical information concerning the topography and hydrology of the study area. Elevation data, flood flow directions, and identification of vulnerable regions were among the key findings derived from the DEM analysis. The elevation levels captured by the DEM ranged from 0 to 2663 m within the study area (Fig.  4 a).

The researchers employed ArcGIS software to generate three essential maps using the DEM data: slope, aspect, and hill shade maps to gain a deeper understanding of the topographic features. These maps provided distinct perspectives on the terrain’s characteristics. The slope map (Fig.  5 a) vividly illustrated the steepness of the rocks in the study area, with higher slope values indicating more pronounced inclinations. The aspect map (Fig.  5 b) revealed that slopes predominantly faced southward within the study area. Furthermore, the hill shade map (Fig.  5 c), employing shading techniques, effectively portrayed the topographical features of hills and mountains. It accentuated relative slopes and mountain ridges, notably highlighting the valley of Al-Lith as particularly susceptible to flood hazards (Table 2 ).

( a ) Slope map of the area under investigation, ( b ) aspect map of the area under investigation, ( c ) Hill shade map of the area under investigation. [created using 34 .

Monthly precipitation data (Table 3 ) were scrutinized to understand the precipitation patterns in the Al-Lith area. The analysis revealed that the average annual precipitation in the area amounted to approximately 9.3 mm. Notably, January, November, and December were identified as the months with the highest recorded rainfall levels, as per data sourced from climate-data.org. The combination of these factors suggests that while Al-Lith typically experiences low annual precipitation, the region is highly susceptible to flash floods during specific months which are January, November, and December. This primary flood risk occurs due to significantly higher precipitation levels during these months, where rainfall is significantly higher. The last historical floods happened in November 2018 and December 2022.

As a combined result of the above, this study harnessed the power of the DEM to conduct an in-depth analysis of the study area's drainage network, stream orders, and topographical features. ArcGIS software facilitated the creation of informative slope, aspect, and hill shade maps, shedding light on the terrain’s characteristics and emphasizing flood vulnerabilities in Al-Lith Valley. Furthermore, the examination of monthly precipitation data unveiled the region’s average annual rainfall patterns, highlighting specific months of heightened precipitation (Table 4 ). These integrated findings contribute to a comprehensive understanding of the study area's hydrological and topographic dynamics, which are crucial for flood risk assessment and mitigation efforts.

Morphometric parameters analysis

In the assessment of the study area’s morphometric characteristics, several key parameters were examined to gain valuable insights into its drainage network and hydrological behavior.

Drainage density (Dd)

Drainage density (Dd) serves as a fundamental metric, calculated as the total length of streams within a drainage basin divided by its area (A). In the present research region, a notably low drainage density of 1.19 km −1 is observed, indicative of a scarcity of streams relative to the area’s expanse. This characteristic can be primarily attributed to the presence of erosion-resistant, fractured, and rough rock formations that facilitate accelerated water flow within the wadi 26 .

Stream frequency (Fs)

Stream frequency (Fs) signifies the abundance of streams within a specific area, quantified as the number of streams per unit area. In the studied domain, the stream frequency is calculated to be 3.32 km 2 , revealing a relatively low stream density. This implies a scarcity of streams per square kilometer, a phenomenon influenced by factors such as modest relief, permeable subsurface materials, and a heightened capacity for infiltration. These conditions collectively contribute to the profusion of streams within the region 48 , 49 .

Bifurcation ratio (Rb)

The bifurcation ratio (Rb) provides insights into the branching pattern within a watershed’s stream network. It is computed as the ratio of the number of streams of a given order to the number of streams of the order directly above it. The mean bifurcation ratio (Mbr) in the study area is determined to be 1.96, signifying a notable degree of branching within the watershed’s stream network 49 .

Infiltration number (If)

The infiltration number (If) represents a comprehensive metric evaluating the infiltration capacity of a watershed, factoring in both drainage density and stream frequency. In the research region, the calculated infiltration number is 3.95, categorizing it as exhibiting low infiltration numbers and high runoff potential. This observation underscores the area’s propensity for high runoff rates due to its limited infiltration capacity 49 .

Flood risk assessment and site suitability

The interplay of drainage density, stream frequency, bifurcation ratio, and infiltration number impart significant insights into the watershed's characteristics and hydrological behavior. Notably, the low drainage density, low stream frequency, high bifurcation ratio, and low infiltration number in the study area collectively contribute to elevated flood risk and heightened potential for runoff. This assessment underscores the imperative necessity for the implementation of effective flood mitigation measures within the region.

Furthermore, a holistic approach was applied by 50 involving the interrelationship of bifurcation ratio, drainage frequency, and drainage density to evaluate the basin’s hazard potential. Based on this analysis, the studied basin is identified as having a considerable likelihood of experiencing flash floods.

Briefly, the comprehensive analysis of morphometric parameters reveals critical insights into the study area’s hydrological behavior and flood risk. The observed characteristics necessitate diligent attention to flood risk mitigation strategies and effective management practices within the region.

Geophysical data processing and interpretation

In the aftermath of an extensive field survey conducted within the study area, a meticulous and structured data processing sequence is enacted. This sequence encompasses several crucial steps geared toward enhancing data consistency and reliability.

Data quality assessment

The initial phase of data processing revolves around the generation of apparent resistance curves employing the field data. These curves serve the pivotal function of identifying and rectifying any irregularities, with particular emphasis on anomalies encountered during the onset of electrical and electromagnetic tests. Aberrant readings undergo rigorous scrutiny and, where necessary, are expunged from the dataset to elevate the overall precision and fidelity of the information.

Utilization of data processing software

Subsequently, specialized data processing software tools come into play, specifically the “Interpex 1DIV” 51 and “ZondTEM1D” 52 programs. These meticulously designed programs take on the responsibility of processing data originating from electrical probes. The dataset encompasses critical information, including electrical resistance, and, in applicable scenarios, resistance and inductive polarization. The primary probe data collected from the study site serves as the foundational data set for this comprehensive processing (Fig.  3 b, c).

Development of a multi-layers model

The third phase in the data processing continuum is marked by efforts to streamline the representation of multi-layered data into a more coherent and manageable form. This procedure necessitates the amalgamation of groups of closely associated resistance values into unified composite resistance layers. The primary objective is to streamline the dataset’s complexity while preserving its intrinsic geoelectric attributes and characteristics.

Characterization of geoelectric layers

The ultimate stage of data processing culminates in the meticulous characterization of geoelectric layers. This encompasses the precise determination of electrical resistivity values, layer thicknesses, and the depths of the discrete geoelectric strata. These defined parameters offer a comprehensive understanding of the geological and geophysical attributes of the study area.

Geophysical insights

The geophysical investigation, with a specific focus on the vicinity proximate to the groundwater dam and the Wadi Al-Leith water station within Wadi Al-Laith, has yielded valuable insights. The primary aim was to harness the dam’s influence on nearby wells, thus mitigating the necessity for extensive station-to-well extensions. Concurrently, the presence of a fractured layer and the heterogeneous topography of the solid base rocks were meticulously documented.

The amalgamated findings underscore the existence of a substantial and adequately saturated sedimentary layer at select locations, coexisting alongside a cracked rocky layer harboring a discernible water content. It is pertinent to note that the predominant characteristic across the valley’s expanse is the prevalence of a notably thin sedimentary layer, characterized by limited water saturation (Fig.  6 ). It is clear from the interpretations that the depth of groundwater in the investigation area ranges from 0.5 to 14 m (Fig.  6 a), and the thickness of the layer containing the water ranges between 0.3 and 33.63 m (Fig.  6 b). The inference of the presence of groundwater was confirmed by an actual review of the results of the electrical resistance values, which ranged from 33.9 to 145 Ω.m (Fig.  6 c).

( a ) Depth map to groundwater bearing layer, ( b ) thickness map of groundwater bearing layer, ( c ) resistivity distributions map of groundwater bearing layer, ( d ) map of hypothetical score calculation by geophysical weighted decision matrix [created using 26 .

In summation, the comprehensive geophysical investigation has unveiled the coexistence of well-saturated sedimentary layers and fractured rocky substrates across the study area. These findings constitute a pivotal resource for groundwater assessment and the judicious utilization of resources within the Wadi Al-Laith region.

Matrix of comparative assessment of dam site suitability

Matrix of the effective geoelectrical model for dam site suitability.

Matrices have been mentioned, as one of the means of evaluating the preference for identifying areas, in many studies that deal with environmental and water assessment processes for proposing or evaluating areas for constructing dams, such as 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 . The matrices differed in many of them depending on the parameters used and the data available (Tables S1 and S2 supplementary information documents). In this research, a somewhat unique matrix was designed based on the availability of data and the amount of correlation and complementarity between them.

In the comprehensive assessment of the geoelectric model of sublayers as an effective parameter in the suitability matrix for both the first and second regions, a series of parameters were carefully considered, each assigned a weight percentage to reflect its relative importance in the decision-making process. These parameters encompassed critical aspects of the geoelectrical model of sublayers and related factors, including layer resistivity (ρ), layer thickness (h), layer geometry, layer boundaries, electrode configuration, data quality and error estimation, inversion algorithm, geological constraints, and hydrogeological properties (Tables S3 and S4 supplementary information documents).

The weighted decision matrices for both regions were constructed by evaluating the effectiveness of each parameter for its effective power in site suitability. A hypothetical score calculation was then performed by multiplying the weight percentage by the effectiveness score for each parameter and summing these values for each region (Table 5 , Fig.  6 d). The results revealed that the second region excelled in suitability, achieving an impressive score of 60%, whereas the first region scored lower at 40%. This suggests that the second region is significantly more favorable for dam construction, as determined by the geoelectrical model of sublayers and its associated suitability parameters.

Matrix of dam site suitability

In the evaluation of suitable locations for building a dam within the first and second regions, a set of parameters and their respective weightings were considered. These parameters included bifurcation ratio (Mbr), aspect, slope, hill shade of the study area, annual average precipitation, stream length (Lu), drainage density (Dd), stream frequency (Fs), drainage intensity (Di), infiltration number (If), flood possibilities, and the geoelectrical model of sublayers (Table 6 ). Each parameter was assigned a weight percentage reflecting its relative importance in the decision-making process. Subsequently, weighted decision matrices were created for both regions, where the quality of each parameter was assessed for each location.

The hypothetical score calculation was performed by multiplying the weight percentage by the quality score for each parameter and summing these values for each region. Based on this analysis, the first region, where the old dam was located, received a suitability score of 44%, while the second region scored higher at 56%, suggesting that the second region may be a more suitable option for building a dam according to the specified criteria (Fig.  7 ).

Map of hypothetical score calculation by hydrogeological and geophysical weighted decision matrix. Created using 26 .

Evaluating dam site suitability

The assessment conducted through matrix analysis has yielded valuable insights into the suitability of potential dam sites in the specified regions. These findings are rooted in a meticulous evaluation of various parameters and their weighted contributions to the overall suitability score. In this context, the first region emerged with a suitability score of 44%, while the second region demonstrated a notably higher score of 56%. This discrepancy in scores underscores a critical distinction between the two regions in terms of their potential for dam construction (Fig.  7 ).

The higher score awarded to the second region suggests that it may hold distinct advantages when measured against the specific criteria used for evaluation. These criteria, which include factors like bifurcation ratio (Mbr), aspect, slope, hill shade of the study area, annual average precipitation, stream length (Lu), drainage density (Dd), stream frequency (Fs), drainage intensity (Di), infiltration number (If), flood possibilities, and the geoelectrical model of sublayers depended on geoelectrical properties, geological constraints, and hydrogeological considerations, collectively indicate a higher level of suitability for dam construction in the second region. This implies that the second region offers a more promising and feasible prospect for establishing a dam infrastructure, aligning closely with the predefined objectives and prerequisites of the project. As such, the findings of this analysis provide a compelling rationale for considering the second region as the preferred choice for future dam construction endeavors.

Parameters of proposed dam

Although it is impossible to completely eliminate the risk of flash floods, there are a variety of strategies to lessen it. For example, it is possible to identify the areas that are most vulnerable to the hazard by analyzing the drainage system, hydrologic modeling, and the local geology. Dams and canals are suggested solutions to the issue in addition to assisting in collecting and replenishing water for various reasons.

The Al-Lith earthen dam in the study area collapsed on November 23, 2018, as a result of repeated rainstorm events in the upper part of Wadi Al-Lith in western Saudi Arabia 64 . An old Al-Lith dam was built as an altocumulus dam to solve this issue. Its height terminates at the earth's surface and its goal is to store groundwater to supply the wells dug above this dam. To supply a purification plant next to the old dam, a number of wells needed to be sunk at the top of the old dam (Fig.  8 ).

Map of the calculated storage-capacity volume of the proposed dam which is suggested for the area under investigation. Created using 34 .

Based on the morphological analysis of the watershed and to reduce the risk of flash flooding 50 , the study of work suggests improving the proposed dam so that it can have a storage capacity of about 38,187,221.4 m 3 and an area behind the dam of about 3,567,763.9 m 2 . Additionally, it may advocate building a supporting dam around 5 km south of the old Al-Lith Dam. Geologically, the site of the proposed and projected new Dam will be constructed on the two wadi sides with hard rock of quartz–diorite and no faults. The newly proposed dam will have a storage capacity of 114,624,651.1 m 3 , and its size will be 5,104,646.8 m 2 (Fig.  8 ). According to GIS analysis, if the elevation map of the study area ranges from 122 to 617 m, the suggested proposed dam should measure between 230 and 280 m in height and 800 m in length.

The hydrogeological modeling conducted in this study leverages Digital Elevation Model (DEM) data to delineate the drainage network of Wadi Lith, revealing key insights into the region's susceptibility to flood hazards. The DEM analysis underscores the dominance of first-order streams (SU1) in the area, indicating a heightened vulnerability to drainage-related issues. The slope, aspect, and hill shade maps generated using ArcGIS further enhance our understanding of the region’s topography. The slope map highlights areas of steep inclinations, the aspect map shows a predominance of south-facing slopes, and the hill shade map vividly portrays the valley’s topographical features, emphasizing the Al-Lith Valley’s susceptibility to floods.

The analysis of morphometric parameters offers a comprehensive understanding of the drainage characteristics and flood risks within the study area. Drainage density (Dd) shows a value of 1.19 km −1 , the low drainage density indicates a scarcity of streams, attributed to erosion-resistant rock formations that facilitate rapid water flow, contributing to flood risk. Stream Frequency (Fs) shows at 3.32 km 2 , the relatively low stream frequency suggests limited stream presence, influenced by modest relief and high infiltration capacity. The bifurcation ratio (Rb) shows a mean value of 1.96 reflecting significant branching within the stream network, crucial for understanding flood dynamics. Infiltration number (If) illustrates the low infiltration number of 3.95 highlights a high runoff potential, underlining the area’s vulnerability to flash floods. These parameters collectively indicate an elevated flood risk and necessitate effective mitigation strategies.

The geophysical investigation, focusing on the area around the groundwater dam and Wadi Al-Leith water station, reveals the coexistence of well-saturated sedimentary layers and fractured rocky substrates. This duality is crucial for groundwater assessment and highlights the potential for utilizing these resources effectively. The identified groundwater depths (0.5–14 m) and layer thicknesses (0.3–33.63 m) are significant for planning water extraction and management strategies.

The matrix analysis for dam site suitability compares two regions, considering various hydrological, geological, and geoelectrical parameters. The geoelectrical model illustrates that the second region scores higher (60%) compared to the first (40%), indicating better suitability for dam construction based on geoelectrical properties. Overall suitability containing factors like bifurcation ratio, aspect, slope, and precipitation illustrates that the second region again scores higher (56%) versus the first (44%). This comprehensive evaluation suggests that the second region is more favorable for dam construction due to its advantageous geoelectrical and topographical characteristics.

Considering the historical collapse of the Al-Lith Dam in November 2018 and December 2022, the study proposes improvements to the dam structure to enhance its storage capacity and flood mitigation capability. The proposed dam should have a storage capacity of approximately 114,624,651.1 m 3 , with a height of 230–280 m and a length of 800 m. This strategic enhancement aims to bolster the region's flood resilience and water management efficiency.

The integrated hydrogeological, geophysical, and morphometric analyses provide a holistic understanding of the flood risks and water management challenges in Wadi Al-Lith. The proposed mitigation strategies, including the construction of a new dam, are grounded in comprehensive geospatial and geophysical data, ensuring their effectiveness in enhancing the region’s flood resilience and water resource management. This study underscores the importance of leveraging advanced geospatial techniques and comprehensive data analysis for effective flood risk mitigation in arid regions.

The study offers a comprehensive evaluation of flood risk mitigation strategies in Wadi Al-Laith, Kingdom of Saudi Arabia (KSA), emphasizing the critical need to address flood risks in arid regions due to their severe impact on communities, infrastructure, livelihoods, and the economy.

By using the hydrological analysis, the investigation of the morphometric parameters revealed low drainage density, low stream frequency, a high bifurcation ratio, and a low infiltration number, indicating elevated flood risk and high runoff potential in Wadi Al-Laith. These characteristics highlight the need for effective flood risk management to protect communities and infrastructure.

By using geophysical investigation, data processing used specialized software 51 , 52 to process electrical and electromagnetic probe data, ensuring accuracy by correcting field data irregularities. The “multi-layer model” was developed by consolidating resistance values and providing detailed information on electrical resistivity, layer thicknesses, and depths of geoelectric strata. Findings include a well-saturated sedimentary layer and a cracked rocky layer with water content, though a thin, less saturated sedimentary layer is predominant. The study area was divided into two regions for dam construction, with the proposed new dam site scoring 56% in suitability, higher than the old dam sites at 44%.

The study indicates the encouragement and support of combining hydrogeological and geophysical data to offer a thorough understanding of factors contributing to flash floods, including topography, drainage characteristics, and subsurface properties.

Long-term implications of constructing dams have environmental Impacts like (1) dams significantly alter natural water flow, which can impact downstream ecosystems. By regulating water flow, dams can reduce the frequency and severity of floods, but they may also reduce sediment transport, affecting riverine habitats and delta formations. (2) The creation of a reservoir can lead to the submersion of land, affecting local flora and fauna. In arid regions like Wadi Al-Laith, this could disrupt unique desert ecosystems (3) Stagnant water in reservoirs can lead to reduced water quality, promoting the growth of algae and affecting aquatic life.

Also, the long-term implications of constructing dams have a morphological response like (1) the dam will trap sediments, leading to sediment accumulation in the reservoir. This can reduce the dam’s storage capacity over time and necessitate periodic dredging. (2) downstream of the dam, reduced sediment supply can lead to channel erosion, altering the geomorphology of the riverbed and potentially impacting infrastructure and habitats.

While acknowledging the potential long-term environmental implications, the decision to propose dam construction is based on a comprehensive assessment of the specific context of Wadi Al-Laith a recommended advice for building an 800 m-long auxiliary dam with a height of 230–280 m, utilizing quartz–diorite rock. Our analysis of morphometric parameters indicates a high flood risk due to low drainage density, low stream frequency, high bifurcation ratio, and low infiltration number. A strategically placed dam can significantly mitigate these risks. Additionally, the selected dam site in the second region, utilizing sturdy quartz–diorite rock without faults, provides a stable foundation for the proposed structure, ensuring its long-term stability and effectiveness. The proposed auxiliary dam, with a detailed design considering height, diameter, relief holes, surface inclinations, and well placements, aims to enhance flood resilience while addressing the specific hydrological and geological conditions of the area.

In addition to proposing dam construction, our study considered several non-structural and nature-based solutions to mitigate flood risk in Wadi Al-Laith, The study underscores the need for a holistic approach to enhance water resource management and support agriculture, and flood risk mitigation in arid regions like KSA, where infrequent but devastating floods can occur. A holistic approach to flood risk mitigation in arid regions like Wadi Al-Lith in the Kingdom of Saudi Arabia should combine structural and non-structural measures to address both immediate flood threats and long-term resilience, considering the unique hydrological and climatic conditions. Key strategies include (1) integrated watershed management, involving catchment area analysis, land use planning, and soil and water conservation; (2) structural measures, such as building dams, flood channels, and retention basins; (3) non-structural measures, including advanced flood forecasting, community engagement, and sustainable water management policies; (4) geophysical and hydrological monitoring through continuous data collection and geophysical surveys; (5) ecosystem-based approaches, such as restoring natural floodplains and promoting green infrastructure; and (6) adaptive management and research to allow flexibility in strategies and support ongoing research. By integrating these measures, advanced monitoring, and active community involvement, a holistic approach can significantly enhance flood resilience in arid regions like Wadi Al-Lith, addressing immediate risks and building long-term sustainability and adaptability to climate change.

The research contributes to flood risk management discourse in KSA by presenting innovative approaches to dam site selection using geophysical and geomorphological modeling. While our study acknowledges the potential long-term environmental implications of dam construction, it also highlights the necessity of such infrastructure in the specific context of Wadi Al-Laith to ensure effective flood risk mitigation. It offers valuable insights and recommendations to protect communities and infrastructure in arid regions prone to flash floods, promoting sustainable development. Findings can guide policymakers, researchers, and practitioners in KSA and similar arid regions globally.

Data availability

All data generated or analyzed during this study are included in this mnuscript.

Sissakian, V. K., Adamo, N. & Al-Ansari, N. The role of geological investigations for dam siting: Mosul Dam a case study. Geotech. Geol. Eng. 38 (2), 2085–2096. https://doi.org/10.1007/s10706-019-01150-2 (2019).

Article   Google Scholar  

Elsebaie, I. H., Kawara, A. Q. & Alnahit, A. O. Mapping and assessment of flood risk in the Wadi Al-Lith Basin, Saudi Arabia. Water 15 (5), 902. https://doi.org/10.3390/w15050902 (2023).

Talebi, A., Mandegar, A. R., Parvizi, S., Poordara, H. & Barkhordari, J. Underground dam site selection using hydrological modelling and analytic network process. Groundw. Sustain. Dev. 23 , 100976. https://doi.org/10.1016/j.gsd.2023.100976 (2023).

Sharma, S. & Mujumdar, P. P. Baseflow significantly contributes to river floods in Peninsular India. Sci. Rep. 14 (1), 1251 (2024).

Article   ADS   CAS   PubMed   PubMed Central   Google Scholar  

Lin, C. H. et al. Application of geophysical methods in a dam project: Life cycle perspective and Taiwan experience. J. Appl. Geophys. 158 , 82–92. https://doi.org/10.1016/j.jappgeo.2018.07.012 (2018).

Article   ADS   Google Scholar  

Fedorov, M., Badenko, V., Maslikov, V. & Chusov, A. Site selection for flood detention basins with minimum environmental impact. Procedia Eng. 165 , 1629–1636. https://doi.org/10.1016/j.proeng.2016.11.903 (2016).

Sadiq, A. A., Tyler, J. & Noonan, D. S. A review of community flood risk management studies in the United States. Int. J. Disaster Risk Reduct. 41 , 101327. https://doi.org/10.1016/j.ijdrr.2019.101327 (2019).

Havenith, H. B., Torgoev, I. & Ischuk, A. Integrated geophysical–geological 3D model of the right-bank slope downstream from the Rogun Dam construction site, Tajikistan. Int. J. Geophys. 2018 , 1–16. https://doi.org/10.1155/2018/1641789 (2018).

Oyedele, K. F., Oladele, S. & Nduka, A. C. Integrated geotechnical and geophysical investigation of a proposed construction site at Mowe, Southwestern Nigeria. GeoSci. Eng. 64 (3), 21–29. https://doi.org/10.2478/gse-2018-0014 (2018).

Jozaghi, A. et al. A comparative study of the AHP and TOPSIS techniques for dam site selection using GIS: A case study of sistan and Baluchestan province, Iran. Geosciences 8 (12), 494. https://doi.org/10.3390/geosciences8120494 (2018).

Othman, A. A. et al. GIS-based modeling for selection of dam sites in the Kurdistan Region, Iraq. ISPRS Int. J. Geo-Inf. 9 (4), 244. https://doi.org/10.3390/ijgi9040244 (2020).

Rather, M. A. et al. Identifying the potential dam sites to avert the risk of catastrophic floods in the Jhelum Basin, Kashmir, NW Himalaya, India. Remote Sens. 14 (7), 1538. https://doi.org/10.3390/rs14071538 (2022).

Ramadan, E. M., Shahin, H. A., Abd-Elhamid, H. F., Zelenakova, M. & Eldeeb, H. M. Evaluation and mitigation of flash flood risks in arid regions: A case study of Wadi Sudr in Egypt. Water 14 (19), 2945. https://doi.org/10.3390/w14192945 (2022).

Karpouza, M. How could students be safe during flood and tsunami events. Int J Disast Risk Re 95 , 103830. https://doi.org/10.1016/j.ijdrr.2023.103830 (2023).

Diaconu, D., Costache, R. & Popa, M. An overview of flood risk analysis methods. Water 13 (4), 474. https://doi.org/10.3390/w13040474 (2021).

Boulange, J., Hanasaki, N., Yamazaki, D. & Pokhrel, Y. Role of dams in reducing global flood exposure under climate change. Nat. Commun. https://doi.org/10.1038/s41467-020-20704-0 (2021).

Article   PubMed   PubMed Central   Google Scholar  

Rahmani, F. & Fattahi, M. H. Investigation of alterations in droughts and floods patterns induced by climate change. Acta Geophys. 72 (1), 405–418. https://doi.org/10.1007/s11600-023-01043-2 (2024).

Skilodimou, H. D. & Bathrellos, G. D. Natural and technological hazards in urban areas: Assessment. Plan. Solut. Sustain. 13 (15), 8301. https://doi.org/10.3390/su13158301 (2021).

Cencetti, C. & Di Matteo, L. Mitigation measures preventing floods from landslide dams: Analysis of pre- and post-hydrologic conditions upstream a seismic-induced landslide dam in Central Italy. Environ. Earth Sci. https://doi.org/10.1007/s12665-022-10515-5 (2022).

Ibrahim, A. S. et al. Identifying cost-effective locations of storage dams for rainfall harvesting and flash flood mitigation in arid and semi-arid regions. J. Hydrol. Reg. Stud. 50 , 101526. https://doi.org/10.1016/j.ejrh.2023.101526 (2023).

Hamza, M. H. & Saegh, A. M. Flash flood risk assessment due to a possible dam break in urban arid environment, the new Um Al-Khair Dam case study, Jeddah, Saudi Arabia. Sustainability 15 (2), 1074. https://doi.org/10.3390/su15021074 (2023).

Al-Amri, N. S., Abdurahman, S. G. & Elfeki, A. M. Modeling aquifer responses from flash flood events through ephemeral stream beds: Case studies from Saudi Arabia. Water 15 (15), 2735. https://doi.org/10.3390/w15152735 (2023).

Khan, M. Y. A., ElKashouty, M., Subyani, A. M. & Tian, F. Morphometric determination and digital geological mapping by RS and GIS techniques in Aseer-Jazan contact, Southwest Saudi Arabia. Water 15 (13), 2438. https://doi.org/10.3390/w15132438 (2023).

Article   CAS   Google Scholar  

Alqreai, F. N. & Altuwaijri, H. A. Assessing the hazard degree of Wadi Malham Basin in Saudi Arabia and its impact on north train railway infrastructure. ISPRS Int. J. Geo-Inf. 12 (9), 380. https://doi.org/10.3390/ijgi12090380 (2023).

Odersky, M. & Löffler, M. Differential exposure to climate change? Evidence from the 2021 floods in Germany. J. Econ. Inequal. https://doi.org/10.1007/s10888-023-09605-6 (2024).

Surfer V.15.5.382 (64-bit). Golden Software, LLC. https://www.goldensoftware.com/products/surfer/ . Accessed 7 Jun 2018. (2018).

Bajabaa, S., Masoud, M. & Al-Amri, N. Flash flood hazard mapping based on quantitative hydrology, geomorphology and GIS techniques (case study of Wadi Al Lith, Saudi Arabia). Arab. J. Geosci. 7 , 2469–2481. https://doi.org/10.1007/s12517-013-0941-2 (2014).

Lashin, A., Chandrasekharam, D., Al Arifi, N., Al Bassam, A. & Varun, C. Geothermal energy resources of Wadi Al-Lith, Saudi Arabia. J. Afr. Earth Sci. 97 , 357–367. https://doi.org/10.1016/j.jafrearsci.2014.05.016 (2014).

Article   ADS   CAS   Google Scholar  

Rahman, K. U., Balkhair, K. S., Almazroui, M. & Masood, A. Sub-catchments flow losses computation using Muskingum-Cunge routing method and HEC-HMS GIS based techniques, case study of Wadi Al-Lith, Saudi Arabia. Model. Earth Syst. Environ. 3 , 4. https://doi.org/10.1007/s40808-017-0268-1 (2017).

Hussein, M. T., Lashin, A., Al Bassam, A., Al Arifi, N. & Al Zahrani, I. Geothermal power potential at the western coastal part of Saudi Arabia. Renew. Sustain. Energy Rev. 26 , 668–684. https://doi.org/10.1016/j.rser.2013.05.073 (2013).

Amin, A. A. & Mesaed, A. A. The role of the geologic and the geomorphologic factors in the formation of some geotourism sites of Saudi Arabia. In Geotourism in the Middle East. Geoheritage, Geoparks and Geotourism (eds Allan, M. & Dowling, R.) (Springer, 2023).

Google Scholar  

Ejaz, N., Bahrawi, J., Alghamdi, K. M., Rahman, K. U. & Shang, S. Drought monitoring using landsat derived indices and google earth engine platform: A case study from Al-Lith Watershed, Kingdom of Saudi Arabia. Remote Sens. 15 (4), 984. https://doi.org/10.3390/rs15040984 (2023).

ASTER Global Digital Elevation Model (GDEM) Version 3. https://asterweb.jpl.nasa.gov/gdem.asp (2019).

ESRI. ArcGIS Desktop: Release 10.4.1. [Software]. Environmental Systems Research Institute. https://desktop.arcgis.com/en/quick-start-guides/10.4/arcgis-desktop-quick-start-guide.htm (2016).

Horton, R. E. Drainage basin characteristics. Trans. Am. Geophys. Un. 13 , 350–361 (1932).

Faniran, A. The index of drainage intensity—A provisional new drainage factor. Aust. J. Sci. 31 , 328–330 (1968).

Dobrin, M. B. & Savit, C. H. Introduction to Geophysical Prospecting (McGraw-hill, 1960).

Telford, W. M., Geldart, L. P. & Sheriff, R. E. Applied Geophysics (Cambridge University Press, 1990).

Book   Google Scholar  

Mussett, A. E. Applied geophysics by WM Telford, LP Geldart and RE Sheriff, Cambridge University Press, 1991. No. of pages: 770. Price £ 65.00 (hardback), £ 25.00 (soft cover). Geol. J. 27 , 97 (1992).

Reynolds, J. M. An Introduction to Applied and Environmental Geophysics (John Wiley & Sons, 2011).

Vogelsang, D. Environmental Geophysics: A Practical Guide (Springer Science & Business Media, 2012).

Dentith, M. & Mudge, S. T. Geophysics for the Mineral Exploration Geoscientist (Cambridge University Press, 2014).

ARES II - 10- CHANNEL AUTOMATIC RESISTIVITY SYSTEM. http://www.gfinstruments.cz/index.php?menu=gi&cont=aresII_ov .

Nabighian, M. N. In Electromagnetic Methods in Applied Geophysics Theory (ed. Nabighian, M. N.) (Society of Exploration Geophysicists, 1988).

Chapter   Google Scholar  

Hoekstra, P. & Blohm, M. W. Case histories of time-domain electromagnetic soundings in environmental geophysics. In Geotechnical an Environmental Geophysics: Volume II: Environmental and Groundwater 1–16 (Society of Exploration Geophysicists, 1990).

Ward, S. H. In Geotechnical an Environmental Geophysics: Volume I: Review and Tutorial (ed. Ward, S. H.) (Society of Exploration Geophysicists, 1990).

Burger, H. R., Sheehan, A. F. & Jones, C. H. Introduction to Applied Geophysics: Exploring the Shallow Subsurface (Cambridge University Press, 2023).

Reddy, G. P., Maji, A. K. & Gajbhiye, K. S. Drainage morphometry and its influence on landform characteristics in basaltic terrain, central India—A remote sensing and GIS approach. Int. J. Appl. Earth Obs. Geoinform. 6 , 1–16 (2004).

ADS   Google Scholar  

Prabhakaran, A. & Jawahar Raj, N. Drainage morphometric analysis for assessing form and processes of the watersheds of Pachamalai hills and its adjoinings, Central Tamil Nadu, India. Appl. Water Sci. 8 , 31. https://doi.org/10.1007/s13201-018-0646-5 (2018).

El Shamy, I. Recent recharge and flash flooding opportunities in the Eastern Desert, Egypt. Ann. Geol. Surv. Egypt 18 , 323–334 (1992).

Interpex limited. IX1Dv3.52.exe Software. http://www.interpex.com/ix1d/ix1d.htm (2013).

Zond Software LTD. ZondTEM1Dv22. http://zond-geo.com/english/zond-software/electromagnetic-sounding/zondtem1d/ (2001-2024).

Berhane, G., Amare, M., Gebreyohannes, T. & Walraevens, K. Geological and geophysical investigation of water leakage from two micro-dam reservoirs: Implications for future site selection, northern Ethiopia. J. Afr. Earth Sci. 129 , 82–93 (2017).

Sultan, S. A., Essa, K. S. A. T., Khalil, M. H., El-Nahry, A. E. H. & Galal, A. N. H. Evaluation of groundwater potentiality survey in south Ataqa-northwestern part of Gulf of Suez by using resistivity data and site-selection modeling. NRIAG J. Astron. Geophys. 6 (1), 230–243 (2017).

Attwa, M. & Zamzam, S. An integrated approach of GIS and geoelectrical techniques for wastewater leakage investigations: Active constraint balancing and genetic algorithms application. J. Appl. Geophys. 175 , 103992 (2020).

Attwa, M. et al. Toward an integrated and sustainable water resources management in structurally-controlled watersheds in desert environments using geophysical and remote sensing methods. Sustainability 13 (7), 4004 (2021).

Khan, U. et al. Integrating a GIS-based multi-influence factors model with hydro-geophysical exploration for groundwater potential and hydrogeological assessment: A case study in the Karak Watershed, Northern Pakistan. Water 13 (9), 1255 (2021).

Adesola, G. O., Gwavava, O. & Liu, K. Hydrological evaluation of the groundwater potential in the fractured karoo aquifer using magnetic and electrical resistivity methods: Case study of the Balfour formation, Alice, South Africa. Int. J. Geophys. 1 , 1891759. https://doi.org/10.1155/2023/1891759 (2023).

Ball, J. Use of Geoelectrical Techniques with Numerical Modelling for Surveying and Monitoring of Engineered Water Retaining Structures (Lancaster University, 2023).

Dai, L. et al. Electrical resistivity tomography revealing possible breaching mechanism of a Late Pleistocene long-lasted gigantic rockslide dam in Diexi, China. Landslides 20 , 1449–1463. https://doi.org/10.1007/s10346-023-02048-0 (2023).

Ge, S., Hu, S., Chen, G. & Zhao, Y. Characterization of a leaky earth dam using integrated geophysical surveys. J. Appl. Geophys. https://doi.org/10.1016/j.jappgeo.2023.105099 (2023).

Kadam, A. K. et al. Demarcation of subsurface water storage potential zone and identification of artificial recharge site in Vel River watershed of western India: Integrated geospatial and hydrogeological modeling approach. Model. Earth Syst. Environ. 9 , 3263–3278. https://doi.org/10.1007/s40808-022-01656-4 (2023).

Shekar, P. R. & Mathew, A. Assessing groundwater potential zones and artificial recharge sites in the monsoon-fed Murredu river basin, India: An integrated approach using GIS, AHP, and Fuzzy-AHP. Groundw. Sustain. Dev. 23 , 100994. https://doi.org/10.1016/j.gsd.2023.100994 (2023).

Youssef, A. M., Abu-Abdullah, M. M., AlFadail, E. A., Skilodimou, H. D. & Bathrellos, G. D. The devastating flood in the arid region a consequence of rainfall and dam failure: Case study, Al-Lith flood on 23th November 2018, Kingdom of Saudi Arabia. Z. Geomorphol. 63 , 115–136. https://doi.org/10.1127/zfg/2021/0672 (2021).

Download references

Acknowledgements

Special thanks to Dr. Nihal Adel ([email protected]), Associate Professor of English, Department of English Language, Faculty of Al-Alsun, Minya University, Egypt, for reviewing the linguistic, grammar, and scientific moral context of the current research.

Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB).

Author information

Authors and affiliations.

Geology Department, Faculty of Science, Helwan University, Ain Helwan, Cairo, 11795, Egypt

Adel Kotb & Alhussein Adham Basheer

Geoelectric and Geomagnetism Department, National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Cairo, 11421, Egypt

Ayman I. Taha

Geological Sciences Department, National Research Centre (NRC), 33 El Bohouth St. (Former El-Tahrir St.), Dokki, Giza, 12622, Egypt

Ahmed A. Elnazer

You can also search for this author in PubMed   Google Scholar

Contributions

All authors contributed to all sections and work stages, field measurements, data collection and measurements using geophysical equipment and reviewed the manuscript. A. K. wrote the theoretical part, research methods, removed the deficiencies that appeared after the interpretation, and strengthened the main parts of the research, wrote the summary and conclusions part, reviewed the research parts, maintained a reduction in the percentage of plagiarism, made tables and arranged the forms to match the idea and form of the research, prepare files to confirm the journal requirements and then submitted the research to the journal after approval rest of the authors. A. I. T. developed the field work plan and acquired the data. A. A. E. contributed to the data interpretation, reviewed the research and arranged its parts. A. A. B wrote the text of the manuscript, developed the field work plan with the first and second authors, coordinated the text, wrote the summary and conclusions part with the first author, reviewed the research parts, maintained a reduction in the percentage of plagiarism with the first author, made tables and arranged the forms to match the idea and form of the research with the first author.

Corresponding author

Correspondence to Adel Kotb .

Ethics declarations

Competing interests.

The authors declare no competing interests.

Additional information

Publisher's note.

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary Information

Supplementary tables., rights and permissions.

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/ .

Reprints and permissions

About this article

Cite this article.

Kotb, A., Taha, A.I., Elnazer, A.A. et al. Global insights on flood risk mitigation in arid regions using geomorphological and geophysical modeling from a local case study. Sci Rep 14 , 19975 (2024). https://doi.org/10.1038/s41598-024-69541-x

Download citation

Received : 11 February 2024

Accepted : 06 August 2024

Published : 28 August 2024

DOI : https://doi.org/10.1038/s41598-024-69541-x

Share this article

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Mitigating the flood danger
• Arid regions
• Geomorphological analysis
• Geophysical modeling
• Hydrological assessment
• Dam site selection
• Wadi Al-Laith
• Saudi Arabia

By submitting a comment you agree to abide by our Terms and Community Guidelines . If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Quick links

• Explore articles by subject
• Guide to authors
• Editorial policies

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.