Flood Hazard Mitigation Research Articles

Modeling Flash Floods and Induced Recharge into Alluvial Aquifers Using Multi-Temporal Remote Sensing and Electrical Resistivity Imaging

Flash flood hazard assessments, mitigation measures, and water harvesting efforts in desert environments are often challenged by data scarcity on the basin scale. The present study, using the Wadi Atfeh catchment as a test site, integrates remote sensing datasets with field and geoelectrical measurements to assess flash flood hazards, suggest mitigation measures, and to examine the recharge to the alluvium aquifer. The estimated peak discharge of the 13 March 2020 flood event was 97 m3/h, which exceeded the capacity of the culverts beneath the Eastern Military Highway (64 m3/h), and a new dam was suggested, where 75% of the catchment could be controlled. The monitoring of water infiltration into the alluvium aquifer using time-lapse electrical resistivity measurements along a fixed profile showed a limited connection between the wetted surficial sediments and the water table. Throughflow is probably the main source of recharge to the aquifer rather than vertical infiltration at the basin outlet. The findings suggest further measures to avoid the negative impacts of flash floods at the Wadi Atfeh catchment and similar basins in the Eastern Desert of Egypt. Furthermore, future hydrological studies in desert environments should take into consideration the major role of the throughflow in alluvium aquifer recharge.

Flash flood risk assessment using geospatial technology in Shewa Robit town, Ethiopia

Flash flood is an extreme flooding event which is quick, short-lived, hazardous phenomena having negative environmental and socio-economic impacts. Flood risk management is essential to reduce the effects of flood on human lives and livelihoods. The main goals of this research were flash flood risk analysis and risk quantification in terms of land use land cover using geo-spatial technology in Shewa Robit town. In the present study, elevation, slope, drainage density, distance from river, NDVI, land use land cover, topographic wetness index and curvature were used as parameters determining flash flood risk. To realize these research objectives, all these data were reclassified in to five classes and different weights for each of them was assigned using analytic hierarchy process. Weighted Sum Overlay (WSO) analyses of ARC GIS software was employed to produce flood vulnerability map. Then, the accuracy of generated flood risk map was validated using historical flood data. According to the result, about 3.08%, 14.62% and 20.66% of Shewa Robit town are at a very high, high and moderate flash flood risk, respectively. In addition to this, flood risk was also quantified in terms of land use land cover. The result indicates that the settlement land use is the most vulnerable with an estimated area of 12.01 ha, 99.57 ha and 174.16 ha in very high, high and moderate risk classes. The outcome of the study will be applicable in flood hazard management and mitigation strategies.

Effectiveness of Nature-Based Solutions in Mitigating Flood Hazard in a Mediterranean Peri-Urban Catchment

Urbanization alters natural hydrological processes and enhances runoff, which affects flood hazard. Interest in nature-based solutions (NBS) for sustainable mitigation and adaptation to urban floods is growing, but the magnitudes of NBS effects are still poorly investigated. This study explores the potential of NBS for flood hazard mitigation in a small peri-urban catchment in central Portugal, prone to flash floods driven by urbanization and short but intense rainfall events typical of the Mediterranean region. Flood extent and flood depth are assessed by manually coupling the hydrologic HEC-HMS and hydraulic HEC-RAS models. The coupled model was run for single rainfall events with recurrence periods of 10–, 20–, 50–, and 100–years, considering four simulation scenarios: current conditions (without NBS), and with an upslope NBS, a downslope NBS, and a combination of both. The model-simulation approach provides good estimates of flood magnitude (NSE = 0.91, RMSE = 0.08, MAE = 0.07, R2 = 0.93), and shows that diverting streamflow into abandoned fields has positive impacts in mitigating downslope flood hazard. The implementation of an upslope NBS can decrease the water depth at the catchment outlet by 0.02 m, whereas a downslope NBS can reduce it from 0.10 m to 0.23 m for increasing return periods. Combined upslope and downslope NBS have a marginal additional impact in reducing water depth, ranging from 0.11 m to 0.24 m for 10– and 100–year floods. Decreases in water depth provided by NBS are useful in flood mitigation and adaptation within the peri-urban catchment. A network of NBS, rather than small isolated strategies, needs to be created for efficient flood-risk management at a larger scale.

Sensitivity of Flood Hazard and Damage to Modelling Approaches

Combination of uncertainties in water level and wave height predictions for extreme storms can result in unacceptable levels of error, rendering flood hazard assessment frameworks less useful. A 2D inundation model, LISFLOOD-FP, was used to quantify sensitivity of flooding to uncertainty in coastal hazard conditions and method used to force the coastal boundary of the model. It is shown that flood inundation is more sensitive to small changes in coastal hazard conditions due to the setup of the regional model, than the approach used to apply these conditions as boundary forcing. Once the threshold for flooding is exceeded, a few centimetres increase in combined water level and wave height increases both the inundation and consequent damage costs. Improved quantification of uncertainty in inundation assessments can aid long-term coastal flood hazard mitigation and adaptation strategies, to increase confidence in knowledge of how coastlines will respond to future changes in sea-level.

Ensemble fuzzy MCDM for spatial assessment of flood susceptibility in Ibadan, Nigeria

Ibadan, one of the largest cities in West Africa, experiences recurrent flood hazards, causing severe damages to lives and properties. Although various flood susceptibility models have evolved to mitigate flood hazards in different parts of the world, model performances vary according to the peculiarity of the study area and conditioning factors. Therefore, specialized studies are essential to determine model performances for specific locations. This study develops an integrated spatial multi-criteria decision-making model to classify flood susceptibility in Ibadan, Nigeria. For the improvement of the weighting accuracy of the flood causative criteria, Fuzzy AHP (FAHP) was integrated with GIS for the weight computation and overlay process. Ten flood causative factors were evaluated using the AHP and FAHP models. Results indicate rainfall, runoff, and distance to stream as the most significant flood causative factors with FAHP and AHP weights of 22%, 18%, 16%, and 23%, 23%, 18%, respectively. The FAHP and AHP maps identified the southern region as the most susceptible, with the FAHP also highlighting the susceptibility of the central region. The models’ accuracies were validated by overlaying the AHP and FAHP maps with locations of previous flood occurrences in the study area. The Fuzzy AHP map had a 91% alignment with the historical flood locations while the AHP model produced a 45% match, confirming the higher accuracy of the FAHP model and suitability for flood susceptibility mapping in Nigeria and other West African cities.

Defining a Topographic Index Threshold to Delineate Hydrologically Sensitive Areas for Water Resources Planning and Management

Hydrologically sensitive areas (HSAs) are runoff-generating areas often targeted for effective water resources planning and management actions. Commonly, HSAs can be mapped as areas in a landscape with a topographic index (TI) greater than a threshold level. This study explored the impact of a gradient of different TI threshold values for delineating HSAs using two popular TIs: a topographic wetness index (TWI) and a soil topographic index (STI). The resultant HSAs for each TI were compared to the Federal Emergency Management Agency (FEMA) 100-year floodplain map in New Jersey and its five water regions. Spatial comparison indicators were used to assess the spatial similarity between the HSAs delineated and the FEMA floodplain map. Such comparisons identified the threshold that delineated HSAs whose spatial distributions were most consistent with the FEMA floodplain at each spatial scale for each TI. For example, the identified threshold for using a TWI to delineate HSAs was 10.5 at the state level; however, this threshold varied by the water region. The HSAs delineated approximate the spatial extent of runoff-contributing areas to the 100-year flood relevant for water resources planning and management actions for flood hazard mitigation.

A New and Simplified Approach for Estimating the Daily River Discharge of the Tibetan Plateau Using Satellite Precipitation: An Initial Study on the Upper Brahmaputra River

Collecting in situ observations from remote, high mountain rivers presents major challenges, yet real-time, high temporal resolution (e.g., daily) discharge data are critical for flood hazard mitigation and river management. In this study, we propose a method for estimating daily river discharge (RD) based on free, operational remote sensing precipitation data (Tropical Rainfall Measuring Mission (TRMM), since 2001). In this method, an exponential filter was implemented to produce a new precipitation time series from daily basin-averaged precipitation data to model the time lag of precipitation in supplying RD, and a linear-regression relationship was constructed between the filtered precipitation time series and observed discharge records. Because of different time lags in the wet season (rainfall-dominant) and dry season (snowfall-dominant), the precipitation data were processed in a segmented way (from June to October and from November to May). The method was evaluated at two hydrological gauging stations in the Upper Brahmaputra (UB) river basin, where Nash–Sutcliffe Efficiency (NSE) coefficients for Nuxia (>0.85) and Yangcun (>0.80) indicate good performance. By using the degree-day method to estimate the snowmelt and acquire the time series of new active precipitation (rainfall plus snowmelt) in the target basins, the discharge estimations were improved (NSE > 0.9 for Nuxia) compared to the original data. This makes the method applicable for most rivers on the Tibetan Plateau, which are fed mainly by precipitation (including snowfall) and are subject to limited human interference. The method also performs well for reanalysis precipitation data (Chinese Meteorological Forcing Dataset (CMFD), 1980–2000). The real-time or historical discharges can be derived from satellite precipitation data (or reanalysis data for earlier historical years) by using our method.

Historic storms and the hidden value of coastal wetlands for nature-based flood defence

Global change amplifies coastal flood risks and motivates a paradigm shift towards nature-based coastal defence, where engineered structures are supplemented with coastal wetlands such as saltmarshes. Although experiments and models indicate that such natural defences can attenuate storm waves, there is still limited field evidence on how much they add safety to engineered structures during severe storms. Using well-documented historic data from the 1717 and 1953 flood disasters in Northwest Europe, we show that saltmarshes can reduce both the chance and impact of the breaching of engineered defences. Historic lessons also reveal a key but unrecognized natural flood defence mechanism: saltmarshes lower flood magnitude by confining breach size when engineered defences have failed, which is shown to be highly effective even with long-term sea level rise. These findings provide new insights into the mechanisms and benefits of nature-based mitigation of flood hazards, and should stimulate the development of novel safety designs that smartly harness different natural coastal defence functions.

Estimating the UK Index Flood: an Improved Spatial Flooding Analysis

Flooding is one of the major natural hazards in the UK. Accurate flood estimation at ungauged catchment is an important component to understand and mitigate flood hazards, but still a difficult issue. This study therefore attempts to explore and improve an index flood estimation model, known as the FEH-QMED model, popular in the UK. It was developed under the assumption that the index flood of QMED, i.e., the median of the set of annual maximum (AMAX) flood data, standing for a flooding level of 2-year return period, can be explained by catchment descriptors. In this study, two fundamentals are empirically explored, including assessing reliability of the nonlinear functional impacts of the catchment descriptors on the logarithmic transformation of QMED, specified by the FEH-QMED model, and the potential to improve the model for more accurate index flood estimation, based on the flooding data of 586 gauged stations across the UK. Through a spatial additive regression analysis, we empirically find that the nonlinear impacts of the catchment descriptors in an updated FEH-QMED model appear reliable. However, spatial correlation tests including Moran’s I and Lagrange multiplier tests show that strong spatial dependence exists in the residuals of, but was not fully taken into account by, the QMED type models. We have therefore empirically established new spatial index flood estimation models by proposing spatial autoregressive models to model the impacts of the neighboring sites. Cross-validation assessments demonstrate that the suggested spatial error-based index flood model outperforms the updated FEH-QMED model with a significant improvement, which is robust in the sense of different error measures, say by a reduction of 13.8% of the mean squared error of prediction, for the UK index flood estimation.

At the Crossroads of Flood Mitigation and Urban Revitalization: Residents’ Perspectives of Shifting Floodplain Governance in the United States Rust Belt

Over the past decade, floods have increased in frequency and intensity, a trend that is expected to intensify over the next twenty-five years. This article addresses an underexamined tension in floodplain governance: how a policy instrument designed to mitigate flood hazards in urban neighborhoods also has the potential to drive changes that may lead to environmental gentrification. Through survey and interview data concentrated in an economically depressed neighborhood in Lansing, Michigan, we explore how floodplain residents perceive their own vulnerability to flooding and interpret neighborhood land-use changes precipitated by shifts in floodplain governance. We found that while residents may recognize their neighborhood is at risk of flooding, they downplay their own vulnerability due in part to overconfidence on structural flood control measures. Relatedly, residents value the state’s new flood risk mitigation program for contributing to neighborhood revitalization, generally without recognizing its flood risk adaptation objectives. Ironically, some elements of floodplain governance may drive the deterioration that necessitates urban revitalization, while others may disenfranchise low-income long-time residents. This case illustrates that shifting floodplain governance towards green infrastructure is not fully comprehensible to some residents, pointing to the need for participatory approaches that create a shared vision for urban floodplain neighborhoods.

A robust approach for comparing conventional and sustainable flood mitigation measures in urban basins

An integrated methodological framework for assessing different flood mitigation measures in urban catchments is presented. The framework comprises hydrologic, hydraulic and economic indices aiming at quantifying the effect of different alternatives regarding flood hazard mitigation. The alternatives evaluated include both conventional drainage solutions and low impact development measures. The conventional drainage solutions were: (i) off-line detention tanks; and (ii) sewer enlargement. The low impact development measures included: (i) green roofs (GR); and (ii) permeable surfaces (PS). Each solution was modeled using SWMM5 with respect to flood reduction effectiveness, and the results were compared to those of the existing condition (i.e., no flood mitigation measures). All the examined solutions were also compared based on their construction and operation and maintenance costs for a typical lifespan (i.e., 30 years). The results of the simulation revealed that both low impact development measures and conventional drainage solutions were highly effective even for storm events with low probability of occurrence. However, sewer enlargement was found to be the best alternative from an economic perspective. Nevertheless, peak at the sewer exit increased and time to peak remained unchanged; as a result, local flooding problems are resolved but downstream flooding problems may be introduced. If other criteria are considered, i.e., traffic obstruction, noise, construction easiness, co-benefits and downstream impacts, low impact development measures become more attractive compared to conventional drainage solutions.

Highways protection from flood hazards, a case study: New Tama road, KSA

Highways in arid regions are highly exposed to damage by floods. This requires intensive analysis of flood quantity, time and direction that can be used to design the suitable protection measures. Flood hazard mitigation can be achieved through calculating quantities and distribution by deriving a rainfall–run-off relationship which plays an important role in watershed managements and protection. This study aims to determine the overflow stream ways crosswise over roads and their stream sizes under various precipitation events of 10, 25, 50 and 100 return periods. This can be used in the planning of the flood alleviation measures to protect the roads from flood hazards. This methodology is applied to a real area, Tama road as a part of King Abdul-Aziz Highway, Kingdom of Saudi Arabia. Recorded data were gathered for the study area, and hydrological models were used for delineation of the study area. The results indicated that the proposed site of the new road is extremely exposed to flash flood hazard and protection measures are essential to protect the road. A system of protection is proposed and designed including 7 channels and 2 culverts to mitigate the flood hazard in the area of study. The proposed mitigation system is fit for protecting this area from flood hazards. Protection of such roads helps to save lives of people and reduce the cost of maintenance and rehabilitation due to damages caused by flood.

Back analysis of breaching process of Baige landslide dam

On October 10 and November 3, 2018, two successive landslides occurred at Baige village, the border between Sichuan Province and Tibet Autonomous Region, in China, which totally dammed the Jinsha River on both occasions. Due to the rapid rise in water level in the “10·10” dammed lake, on October 12, the landslide dam breached naturally with the peak breach flow of about 10,000 m3/s. The residual landslide dam was stacked by the subsequent landslide on November 3, resulting in an even larger dammed lake. Fortunately, the height from the water level in the lake to the dam crest made it possible to construct a spillway to drain the water in the dammed lake to a relatively low level. On November 12, the drainage process began with the peak breach flow of 31,000 m3/s. In this study, based on the detailed records of the breach process of the “11·03” Baige landslide dam and using the developed physically based numerical method, a back analysis was conducted. The numerical method was developed based on the overtopping-induced breach mechanism of landslide dams. An iterative time step algorithm was used to simulate the breach evolution and the hydrograph coupling. The major highlights of the numerical method are the consideration of the breach mechanism of landslide dam, such as the breach morphology evolution process along the streamwise and transverse directions, as well as the variation of soil erodibility with depth and the influence of the presence and absence of a spillway. Comparison of the measured and the calculated results indicated that the numerical method developed in this study can reproduce reasonable breach hydrograph and breach evolution process. The sensitivity analysis showed that the soil erodibility coefficient and the residual dam height significantly influenced the landslide dam breaching process. In addition, it was determined that constructing a spillway before landslide dam breaching is an effective flood hazard mitigation measure for large dammed lakes. However, the availability of the construction conditions and the shape of the spillway should be judged comprehensively according to the rising rate of water level and construction capacity.

Margin of Safety Based Flood Reliability Evaluation of Wastewater Treatment Plants: Part 2- Quantification of Reliability Attributes

In a companion paper (Part 1), the basic concepts are discussed in details. In this paper, the application of the concepts and the proposed methodology in that paper are utilized to set the strategies in order to quantify reliability attributes. The case study is Hunts Point wastewater treatment plant and its sewershed in Bronx, New York City, so that it could function during flood. The strategies are selected and reliability of the Hunts Point plant is estimated before and after using best management practices (BMPs). Therefore, the copula based non-stationary 100–year flood frequency analysis of rainfall and storm surge analyzed in the companion paper (Part 1), are used to obtain the design values of surge and rainfall. A differential evaluation Markov Chain with Bayesian interface is used in that paper for parameter estimation. Because the co-occurrence of surge and rainfall is more critical in coastal areas, the design value resulted from bivariate analysis has been considered in this study. In this Part 2, a multi-criteria decision making (MCDM) approach, which characterized the uncertainty of sub-criteria in load-resistance concept, is applied. The Margin of Safety (MOS) concept is extended to numerically assess a rather non-probabilistic MCDM evaluation of load and resistance to estimate the reliability of the plant. Finally, Effective strategies are selected for flood hazard mitigation to improve the reliability and performance of the plant. The results present an increase of about 46% in reliability after using BMPs. The framework presented in this paper is applicable to other coastal watersheds and could be a platform for addressing some pressing issues in coastal preparedness with impacts on design criteria of coastal infrastructure.

GIS Analysis for Urban Flood Hazard Mitigation in Kaduwela Municipal Council Area

Urban flood hazard is a typical natural disaster that occurs due to the reduction of permeable surfaces as a result of land use conversion and changes in rainfall intensity. It ensures the need of different mitigation strategies such as sufficient drainage system, and it is a simple mitigation measure that can be applied in the ground. This paper is timely due to the lack of research studies undertaken that are related to the study area. Natural disasters, flood hazard, influence of urbanization for urban flood, and negative influence of urban flood in the context of the world and Asian region have been discussed in the available literature. Limited research has been undertaken on urban flood mitigation based on hydrological analysis and run off volume calculation in Kaduwela Municipal Council (KMC) area. With this limitation, this paper focuses on analysing the runoff rainwater volume to mitigate urban flood in 2030 (predicted land use) by calculating the rainwater volume in natural and artificial possible outfalls of each watersheds in KMC. The analysis consists of three phases such as: land use prediction, hydrological analysis, and calculation. A GIS-based land use prediction is simulated to analyse the land use changes in relation to green, blue, and brown fills. The revealed land use conversion is also processing day by day as a result of land use conversion and rapid urbanization which will increase the runoff volume in 2030. A GISbased Hydrological analysis was carried out to identify the outfalls and watersheds of the study area. The possible outfalls function as outlets of runoff water which were collected in each watershed. Runoff volume was calculated by using rational formula (Q = 0.0028CIA) and the parameters of the equation used were the coefficient of land use in 2030, rainfall intensity, and 90 acres portion of the watersheds. A sufficient drainage system was also designed to make KMC a disaster resilient municipality. This research will be important in the process of decision-making and policy implementation in the fields of urban planning and flood mitigation.

Spatial-Temporal Dynamics Land Use/Land Cover Change and Flood Hazard Mapping in the Upstream Citarum Watershed, West Java, Indonesia

Abstract This study presents the information on the dynamics of changes in land use/land cover (LULC) spatially and temporally related to the causes of flooding in the study area. The dynamics of LULC changes have been derived based on the classification of Landsat imagery for the period between 1990 and 2016. Terrain surface classification (TSC) was proposed as a micro-landform classification approach in this study to create flood hazard assessment and mapping that was produced based on the integration of TSC with a probability map for flood inundation, and flood depth information derived from field observation. TSC as the micro-landform classification approach was derived from SRTM30 DEM data. Multi-temporal Sentinel-1 data were used to construct a pattern of historical inundation or past flooding in the study area and also to produce the flood probability map. The results of the study indicate that the proposed flood hazard mapping (FHM) from the TSC as a micro-landform classification approach has the same pattern with the results of the integration of historical inundation or previous floods, as well as field investigations in the study area. This research will remain an important benchmark for planners, policymakers and researchers regarding spatial planning in the study area. In addition, the results can provide important input for sustainable land use plans and strategies for mitigating flood hazards.

Earth Observation-based Damage Assessment of 2018 Flood in Parts of Hadejia-Jama’ are River Basin, Nigeria

Floods, Landslides, Forest fire, Volcanoes, Hurricanes and Tsunami among others are indeed considered as the most natural hazards that cause loosed of resources which includes human lives. Hadejia-Jama’ are River Valley has a well-known seasonal occurrence of floodings with maximum interval of five years incidents historically. Among these disasters floods especially along the river basin particularly in developing nations like Nigeria became a regular disaster with state of frequent occurrences almost seasonally. This study assessed pre-flood and post-flood nature of floodplain along Hadejia-Jama’ are from Jigawa to Tiga Dam in Kano State. Remotely sensed sentinel 2 satellite data and ALOS Digital Surface Model (DSM) was used for the study. The sentinel images were subjected to image pre-processing activities such as geometric correction and radiometric correction. To focus on the flood plain, a 5 km buffer of the area around Hadejia-Jama’are River Basin from Jigawa to Tiga dam were extracted from the data by using the extract/clip tools in ArcGIS 10.3 software. Findings of the study revealed that dominant land use along the floodplain prior to flood include bare surface, patches of agriculture/vegetation, settlement, water body. The study also revealed that patterns of flood damages vary irrespective of the risk with areas like Dawakin Kudu and Garun mallam were witnessing more flood damages than Miga LGA of Jigawa State. It is, therefore, concluded that Earth observation and its applications are useful tools/methods for flood damages assessment and evaluation as well as a basis for taking proactive steps in mitigating flood hazard along floodplains and another flood prone environment.

Hurricane Harvey and Greater Houston households: comparing pre-event preparedness with post-event health effects, event exposures, and recovery.

Most disaster studies rely on convenience sampling and 'after-only' designs to assess impacts. This paper, focusing on Hurricane Harvey (2017) and leveraging a pre-/post-event sample of Greater Houston households (n=71) in the United States, establishes baselines for disaster preparedness and home structure flood hazard mitigation, explores household-level ramifications, and examines how preparedness and mitigation relate to health effects, event exposures, and recovery. Between 70 and 80 per cent of participants instituted preparedness measures. Mitigation actions varied: six per cent had interior drainage systems and 83 per cent had elevated indoor heating/cooling components. Sixty per cent reported home damage. One-half highlighted allergies and two-thirds indicated some level of post-traumatic stress (PTS). Three-quarters worried about family members/friends. The results of generalised linear models revealed that greater pre- event mitigation was associated with fewer physical health problems and adverse experiences, lower PTS, and faster recovery. The study design exposed the broad benefits of home structure flood hazard mitigation for households after Harvey.

Can Citizen Science Promote Flood Risk Communication?

This article explores the challenges facing citizen science as a means of joining the efforts of scientists and flood-risk affected stakeholders in motivating citizen involvement in identifying and mitigating flood risks. While citizen science harbors many advantages, including a penchant for collaborative research and the ability to motivate those affected by floods to work with scientists in elucidating and averting risk, it is not without challenges in its implementation. These include ensuring that scientists are willing to share authority with amateur citizen scientists, providing forums that encourage debate, and encouraging equal voice in developing flood risk mitigation strategies. We assess these challenges by noting the limited application of citizen science to flood-relevant problems in existing research and recommend future research in this area to meaningfully incorporate a “re-imagined” citizen science process that is based on the participatory theoretical framework. We also discuss one case study where the principles of collaboration, debate, and equal voice were put into play in an effort to apply citizen science and—in the long term—mitigate flood hazards in one set of communities.

Flood risk management in Sint Maarten – A coupled agent-based and flood modelling method

Disaster risk reduction is a major concern of small island developing states. Measures to reduce risk should not only be based on the magnitude of physical hazard, but also on the exposure and vulnerability of communities. In this article, we examine flood risk management policies in the Caribbean island of Sint Maarten using coupled agent-based and flood models. The agent-based model is used to model actors' behaviour in relation to urban building development and policies that are designed to reduce flood hazard and communities' vulnerability and exposure. The policies considered in the model are a Beach Policy, a Building and Housing Ordinance, a Flood Zoning policy and hazard mitigation structural measures. The flood model is used to simulate coastal and pluvial floods on the island. Agent behaviour such as building new houses and implementing hazard reduction measures affect the flood model as these actions affect the rainfall-runoff process. The flood maps generated from the updated flood model simulations are then used to assess the impact and update agents’ attributes and behaviour. The simulations results show that low-lying areas are populated, which increases the exposure, and the number of vulnerable houses is also high. Hence, out of the four policies, implementing hazard reduction measures is the most important. Reducing the flood hazard by widening existing drainage channels, constructing new ones and building dykes as coastal flood defence would reduce the hazard, hence reducing the number of flooded houses. As it affects all households on the island, the Building and Housing Ordinance is an important policy to reduce vulnerability. In general, the coupled model outputs can be used to inform policy decision making and provide insights to policymakers on the island.