Storm Surge Flooding Research Articles

Initial soil moisture and soil texture control the impact of storm surges in coastal forests

Flooding and salinization triggered by storm surges threaten the survival of coastal forests. The forest root zone (top 40 cm of soil) is the most affected by surge flooding. Determining the effect of a storm surge on edaphic conditions is essential to estimate vegetation response. Pre-storm soil hydrology could mitigate or enhance the salinization effect, ultimately determining the resilience of the forest. Here we assess the influence of pre-storm soil water content and salinity on storm surge effects in coastal vegetated areas. A 1D model (HYDRUS-1D) is used to simulate saltwater infiltration from above through the unsaturated zone. Different water content and concentration scenarios, along with scenarios with variable storm surge salt concentration, storm surge height and storm surge flooding duration are considered. In soils characterized by silt and clay, the maximum salinized soil depth increases as water content increases, affecting the top 40 cm of soil, except for clay loam soil, for which only the top 20 cm are salinized. In sandy soils, the salinization process involves the entire soil column. The contribution of water content to salinization varies from 12 % to 30 % along the top 40 cm in fine soils. In fine soils, the storm-surge height also becomes relevant. A study case is presented to support the numerical results. Field data confirm that soil water content controls the salinization of the root zone in clay and silt soils. Overall, we conclude that the root zones of coastal forests with clay and silt soils and low water content are the most at risk during storm surges. These events have the potential to radically change edaphic conditions and affect ecosystems.

The global long-term effects of storm surge flooding on human settlements in coastal areas

People in low-lying coastal areas live under the great threat of damage due to coastal flooding from tropical cyclones. Understanding how coastal population settlements react to such events is of high importance for society to consider future adaptation strategies. Here we generate a new global hydrodynamic data set on tropical cyclone-generated storm surge flooding for the period 1851–2020. By combining this data with spatial data on human populations, we analyze the influence of the depth of storm surge flooding on the rural, urban, and total populations in low elevation coastal zones from 1941–2010. We find that in response to a one standard deviation increase in storm surge flooding depth (0.43 m), the exposed population in a 10×10 km low elevation coastal zone decreases by around 970 individuals on average per decade. This reduction corresponds to 9% of the average population living in an exposed grid cell. Tropical cyclone generated wind speed and rainfall do not influence the relocation of coastal populations. The majority of the threatened population lives in Eastern, South–Eastern, and Southern Asia. We show that the exposed coastal population appears to have adapted over time by reducing its exposure in recent decades. This finding applies to all regions other than North America, Oceania, and Western Asia.

Compound Impact of Storm Surge and Flood Characteristics in Coastal Area Based on Copula

In low-lying coastal areas, the interplay of various factors including precipitation, river flow, and storm surge can lead to greater influence on floods when they occur simultaneously. The copula method was used in this study to investigate the bivariate flood risk of compounding storm surge and river discharge events in the Pearl River Delta (PRD). Our results indicate that while the correlation between storm surge and flood peak (S-Q) was weak, there was a strong dependence between the pairs of storm surge–flood volume (S-V) and storm surge–flood duration (S-D). For these three pairs, the Clayton copula was the optimal function for S-Q, while the Frank copula was the optimal function for S-V and S-D, respectively. When the flood volume exceeds 2.0 × 104 m3/s and the flood duration is more than 10 days, the bivariate hydrologic risk for S-V and S-D is observed to decrease rapidly. Furthermore, the failure probability (FP) would be underestimated when the combined impact of river flow and storm surge is ignored in coastal flood risk assessment. Such bivariate hydrologic risk analysis implies that when determining design values in coastal flood risk assessment, the combined impact of river flow and storm surge should be taken into account.

Which Is More Rewarding in Managing Sea-Level Rise and Hurricane Storm Surge Flooding: Mitigation or Response?

This study aims to extend the existing climate-change-induced flood mitigation research. We introduce an at-risk network to evaluate optimal cost–benefit strategies for creating dikes and levees to mitigate flood hazard over multiple years. Our proposed model includes the expected flood costs, estimated using possible climate-change-induced sea-level states throughout the planning horizon, and the investment costs for developing dikes and levees via land elevations across the at-risk network. Further, given the limitations on infrastructure investment, our model incorporates a budget constraint. The problem is modeled as a multistage stochastic program with recourse that minimizes overall expected costs over the planning horizon. Exploiting open-source and freely accessible data sets, the flood risk mitigation model elaborated here can be applied to most urban coastal situations due to its general nature. Using Boston as a case study, our proposed method resulted in a cost reduction of as much as 92.2%, with an average of 63.2%, compared to a “do nothing” strategy in a simulation-based experiment. Under a high sea-level rise scenario, the average cost savings observed by implementing the solution suggested by our model could be even 15% higher. This proposed approach offers decision-makers a tool to frequently assess the costs and risks faced by their cities enabling them to effectively mitigate the potential flooding risks.

Multiphase SPH analysis of a breaking wave impact on elevated structures with vertical and inclined walls

Elevated structures are prevalent along shorelines that are susceptible to storm surge flooding to improve coastal resilience. In this work, we explore the influence of front wall inclination on the pressures and forces attracted by an elevated structure in response to extreme wave impact. Multiphase smoothed-particle hydrodynamics was used to examine a typical two-story building 6 m high and 10 m long with three different frontal wall inclinations impinged by a single breaking wave propagating landwards (from left to right). Relative to a vertical surface, both positive (clockwise) and negative (counterclockwise) inclinations of the front wall altered breaking wave pressures depending on the structure's position relative to the still-water level (SWL). When the bottom of the structure is located below the SWL (negative air gap), a positive inclination decreased breaking wave loads by up to 21 %, while a negative inclination may result in 50 % higher pressure maxima. However, for a structure elevated above the SWL (positive air gap), negative and positive inclinations witnessed reductions to the pressure maxima of 35 % and 10 %, respectively, when compared with a vertical surface.

Ensemble Neural Networks for the Development of Storm Surge Flood Modeling: A Comprehensive Review

This review paper focuses on the use of ensemble neural networks (ENN) in the development of storm surge flood models. Storm surges are a major concern in coastal regions, and accurate flood modeling is essential for effective disaster management. Neural network (NN) ensembles have shown great potential in improving the accuracy and reliability of such models. This paper presents an overview of the latest research on the application of NNs in storm surge flood modeling and covers the principles and concepts of ENNs, various ensemble architectures, the main challenges associated with NN ensemble algorithms, and their potential benefits in improving flood forecasting accuracy. The main part of this paper pertains to the techniques used to combine a mixed set of predictions from multiple NN models. The combination of these models can lead to improved accuracy, robustness, and generalization performance compared to using a single model. However, generating neural network ensembles also requires careful consideration of the trade-offs between model diversity, model complexity, and computational resources. The ensemble must balance these factors to achieve the best performance. The insights presented in this review paper are particularly relevant for researchers and practitioners working in coastal regions where accurate storm surge flood modeling is critical.

Design for Storm Surge Flooding Adaptation: Facilitating Emergency Evacuation with Adaptive Landscape Form-Based Codes

Lack of consensus and funding led to a focus on building retrofits after storm surge flooding and collective inaction for undertaking cross-jurisdictional adaptation pathways planning. Using Seabrook, TX, United States, as a test case, this paper demonstrates the feasibility of using design games (participatory community visioning and design processes) to develop consensus-based, performance-driven, form-based codes from an adaptive landscape framework to facilitate emergency evacuation during storm surge flooding. The framework provides bottom-up mechanisms to enhance the sizes, coverages, quantities, and connectivity of multi-scalar engineered structural and nature-based solutions as a complex adaptive system to increase evacuation time and decrease flood-prone population.

Risk Perception and Preparation for Storm Surge Flooding: A Virtual Workshop with Visualization and Stakeholder Interaction

Abstract Many factors shape public perceptions of extreme weather risk; understanding these factors is important to encourage preparedness. This article describes a novel workshop designed to encourage individual and community decision-making about predicted storm surge flooding. Over 160 U.S. college students participated in this 4-h experience. Distinctive features included 1) two kinds of visualizations, standard weather forecasting graphics versus 3D computer graphics visualization; 2) narrative about a fictitious storm, role-play, and guided discussion of participants’ concerns; and 3) use of an “ethical matrix,” a collective decision-making tool that elicits diverse perspectives based on the lived experiences of diverse stakeholders. Participants experienced a narrative about a hurricane with potential for devastating storm surge flooding on a fictitious coastal college campus. They answered survey questions before, at key points during, and after the narrative, interspersed with forecasts leading to predicted storm landfall. During facilitated breakout groups, participants role-played characters and filled out an ethical matrix. Discussing the matrix encouraged consideration of circumstances impacting evacuation decisions. Participants’ comments suggest several components may have influenced perceptions of personal risk, risks to others, the importance of monitoring weather, and preparing for emergencies. Surprisingly, no differences between the standard forecast graphics versus the immersive, hyperlocal visualizations were detected. Overall, participants’ comments indicate the workshop increased appreciation of others’ evacuation and preparation challenges.

Spatially estimating flooding depths from damage reports

It is important that a sustainable community better prepare for and design mitigation processes for major flooding events, particularly as the climate is non-stationary. In recent years, there have been major storm events in the USA with record amounts of rainfall that some refer to as stalled storms. These stalled storms frequently result in flooding of urban areas which are not subject to riverine or storm surge flooding. This research focuses on using flood damage reports in conjunction with contour maps, geographical information systems, Light Detection and Ranging (LiDAR) data, photographs, and spatial averaging to develop total (high) flood elevation data sets for two neighborhoods for Tropical Storm Imelda in Beaumont, Texas. When various sources of data such as insurance or Federal Emergency Management Agency damage reports, updated LiDAR elevation sets, and coordination data are readily available, this may be an economical method of estimating maximum flood elevations. High-water marks are frequently collected by various agencies as soon as possible after a flooding event, but these data sets might provide even additional information and validation many months or years post an event.

The impacts of tidal wetland loss and coastal development on storm surge damages to people and property: a Hurricane Ike case-study

Coastal wetlands protect communities during hurricanes by reducing storm surge flooding and damages. Previous studies have quantified surge reduction benefits of wetlands, but there is less understanding of how the combination of wetland loss and coastal development influences the spatial distribution of flood extents and damages. In this study we integrate a high-resolution 2-D hydrodynamic model with land-use/land-cover change analyses to assess the effects of total wetland loss, decadal wetland loss, and coastal development on storm surge damages in Galveston Bay, Texas. We measure storm surge flood extents from Hurricane Ike for three scenarios: (i) 2008 Baseline; (ii) 2008 No Wetlands, and (iii) 2019 “Present-day H. Ike”. We find that during Hurricane Ike in 2008, the total loss of coastal wetlands would have increased damages by a net ~ USD $934 million or 12.8% of baseline damages. For the 2019 Present-day H. Ike scenario, we found very few wetlands were lost between 2008 and 2019. If Hurricane Ike had occurred in 2019, damages would have been higher by ~ $2.52 billion or 34.6%, almost entirely due to increased real estate value and new coastal development. Our findings suggest that, while increase in economic exposure is a key driver of storm surge risks in Galveston Bay, effective wetland conservation continues to reduce these risks.

Improving Risk Projection and Mapping of Coastal Flood Hazards Caused by Typhoon-Induced Storm Surges and Extreme Sea Levels

Seawater inundation mapping plays a crucial role in climate change adaptation and flooding risk reduction for coastal low-lying areas. This study presents a new elevation model called the digital impermeable surface model (DISM) based on the topographical data acquired by unmanned aerial vehicle (UAVs) for improving seawater inundation mapping. The proposed DISM model, along with the bathtub model, was used to assess coastal vulnerability to flooding in significant tropical cyclone events in a low-lying region of Victoria Harbor in Hong Kong. The inundation simulations were evaluated based on the typhoon news and reports which indicated the actual storm surge flooding conditions. Our findings revealed that the proposed DISM obtains a higher accuracy than the existing digital elevation model (DEM) and the digital surface model (DSM) with a RMSE of 0.035 m. The DISM demonstrated a higher skill than the DEM and the DSM by better accounting for the water-repellent functionality of each geospatial feature and the water inflow under real-life conditions. The inundation simulations affirmed that at least 88.3% of the inundated areas could be recognized successfully in this newly-designed model. Our findings also revealed that accelerating sea level rise in Victoria Harbor may pose a flooding threat comparable to those induced by super typhoons by the end of the 21st century under two representative emission scenarios (RCP4.5 and RCP8.5). The seawater may overtop the existing protective measures and facilities, making it susceptible to flood-related hazards.

Toward Collaborative Adaptation: Assessing Impacts of Coastal Flooding at the Watershed Scale.

The U.S. Mid-Atlantic coastal region is experiencing higher rates of SLR than the global average, especially in Hampton Roads, Virginia, where this acceleration is primarily driven by land subsidence. The adaptation plans for coastal flooding are generally developed at the municipal level, ignoring the broader spatial implications of flooding outside the individual administrative boundaries. Flood impact assessments at the watershed scale would provide a more holistic perspective on what is needed to synchronize the adaptation efforts between the neighboring administrative units. This paper evaluates flooding impacts from sea level rise (SLR) and storm surge among watersheds in Hampton Roads to identify those most at risk of coastal flooding over different time horizons. It also explores the implications of flooding on the municipalities, the land uses, and land covers throughout this region within the case study watershed. The 2% Annual Exceedance Probability (AEP) storm surge flood hazard data and NOAA's intermediate SLR projections were used to develop flooding scenarios for 2030, 2060, and 2090 and delineate land areas at risk of combined flooding. Findings show that five out of 98 watersheds will substantially increase in inundation, with two intersecting multiple municipalities. They also indicate significant inundation of military, commercial, and industrial land uses and wetland land covers. Flooding will also impact residential land use in urban areas along the Elizabeth River and Hampton city, supporting the need for collaborative adaptation planning on hydrologically influenced spatial scales.

Impact of Storm Surge on the Yellow River Delta: Simulation and Analysis

Storm surges can lead to serious natural hazards and pose great threats to coastal areas, especially developed deltas. Assessing the risk of storm surges on coastal infrastructures is crucial for regional economic development and disaster mitigation. Combining in situ observations, remote sensing retrievals, and numerical simulation, storm surge floods in the Yellow River Delta (YRD) were calculated in different scenarios. The results showed that NE wind can cause the largest flooding area of 630 km2, although the overall storm surge risk in the delta is at lower levels under various conditions. The coastal oilfields are principally at an increasing storm surge risk level. E and NE winds would result in storm surges of 0.9–1.4 m, increasing the risk of flooding in the coastal oilfields. Nearshore seabed erosion in storm events resulted in a decrease in inundation depths and inundation areas. To prevent and control storm surge disasters, we should adapt to local conditions. Different measures should be taken to prevent the disaster of storm surges on different seashores, such as planting saltmarsh vegetation to protect seawalls, while the key point is to construct and maintain seawalls on high-risk shorelines.

Storm surge hazard over Bengal delta: a probabilistic–deterministic modelling approach

Abstract. Storm-surge-induced coastal inundation constitutes a substantial threat to lives and properties along the vast coastline of the Bengal delta. Some of the deadliest cyclones in history made landfall in the Bengal delta region claiming more than half a million lives over the last five decades. Complex hydrodynamics and observational constraints have hindered the understanding of the risk of storm surge flooding of this low-lying (less than 5 m above mean sea level), densely populated (> 150 million) mega-delta. Here, we generated and analysed a storm surge database derived from a large ensemble of 3600 statistically and physically consistent synthetic storm events and a high-resolution storm surge modelling system. The storm surge modelling system is developed based on a custom high-accuracy regional bathymetry enabling us to estimate the surges with high confidence. From the storm surge dataset, we performed a robust probabilistic estimate of the storm surge extremes. Our ensemble estimate shows that there is a diverse range of water level extremes along the coast and the estuaries of the Bengal delta, with well-defined regional patterns. We confirm that the risk of inland storm surge flooding at a given return period is firmly controlled by the presence of coastal embankments and their height. We also conclude that about 10 % of the coastal population is living under the exposure of a 50-year return period inundation under current climate scenarios. In the face of ongoing climate change, which is likely to worsen the future storm surge hazard, we expect our flood maps to provide relevant information for coastal infrastructure engineering, risk zoning, resource allocation, and future research planning.

Assessing household perception, autonomous adaptation and economic value of adaptation benefits: Evidence from West Coast of Peninsular Malaysia

Climate change is causing sea-level rise, intense and frequent storm surge flooding, and significant shoreline erosion in Malaysian coastal areas. Consequently, coastal properties, infrastructure, and livelihoods are threatened. It has become apparent that adaptation at the household and community level is necessary to offset the adverse impacts of coastal hazards. The community needs to be made aware of the risks, acquire knowledge about adaptation options, and be empowered to take their own actions. Public perception and preference are therefore crucial for design and implementation of effective planning for climate change. Thus, this study assesses households' perception, adaptation measures and empirically estimates willingness to pay and preference for planned adaptation measures to guide policy instruments through public engagement. In Malaysia, ten highly vulnerable coastal areas in the Selangor coast were surveyed at the household level (n = 1016) through face-to-face interviews using a structured questionnaire. Regarding households’ perception and adaptation methods, most of the households in the highly exposed areas perceived less risk of inundation and sea-level rise threat and adopted less proactive adaptation and limited risk reduction behaviours during the extreme event. The study found that 66.9% of households were willing to pay for planned adaptation measures despite the limited income capabilities and in favour of moderate adaptation (23.9%). The binomial and ordinal regression results indicated that the probability of willingness to pay for planned adaptation measures significantly increases with age, prior exposure to coastal hazards, awareness, risk perception, community participation, being affected by property damage and loss of income due to extreme events. With increased monthly household income and access to telecommunication services, households will probably pay higher for better adaptation measures. A significant amount of perceived yearly adaptation benefits in the coastal districts revealed the economic value of extensive (22,969.50 MYR/5462.43 USD), moderate (21,853.20 MYR/5196.96 USD) and minimal adaptation measures (8022.90 MYR/1907.94 USD) that can be utilised to incentivise coastal adaptation plans. The findings suggest policies to incorporate social values to reduce vulnerability, enhance community resilience, and contribute to the knowledge gap of adaptation research in the coastal areas.

Controls on coastal flooding in the southern Baltic Sea revealed from the late Holocene sedimentary records

Climate change and related sea-level rise pose significant threats to lowland coasts. However, the role of key controlling factors responsible for the frequency and landward extent of extreme storm surges is not yet fully understood. Here, we present a high-resolution sedimentary record of extreme storm surge flooding from the non-tidal southern Baltic Sea, spanning two periods: 3.6–2.9 ka BP and 0.7 ka BP until present. Sediments from coastal wetland, including sandy event layers, were analyzed by sedimentological (grain size, loss-on-ignition, micromorphology), geochronological (14C), geochemical (XRF), mineralogical (heavy minerals) and micropaleontological (diatoms) methods. The results show that both periods were characterized by high-frequency of storm surge flooding, in order of 1.3–4.2 events per century. These periods correlate with phases of enhanced storminess in northwest Europe and took place during both rising and fluctuating sea levels. The study shows that the frequency and landward extent of coastal inundation, largely depended on the development of natural barriers (e.g. beach ridges and aeolian foredunes). Thus, in the context of the future coastal storm-surge hazard, the protection of existing coastal barriers and their morphology is essential.

A Socioeconomic Dataset of the Risk Associated with the 1% and 0.2% Return Period Stillwater Flood Elevation under Sea-Level Rise for the Northern Gulf of Mexico

Storm surge flooding can cause significant damage to coastal communities. In addition, coastal communities face an increased risk of coastal hazards due to sea-level rise (SLR). This research developed a dataset to communicate the socioeconomic consequences of flooding within the 1% and 0.2% Annual Exceedance Probability Floodplain (AEP) under four SLR scenarios for the Northern Gulf of Mexico region. Assessment methods primarily used HAZUS-MH software, a GIS-based modeling tool developed by the Federal Emergency Management Agency in the United States, to estimate natural disasters’ physical, economic, and social impacts. This dataset consists of 29 shapefiles containing seven different measures of storm surge inundation impacts under SLR (including building damage, displaced people and shelter needs, road exposure, essential facilities, wastewater treatment plants, bridges, and vehicle damage). The data is publicly available under the Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC).

Increased population exposure to Amphan‐scale cyclones under future climates

AbstractSouthern Asia experiences some of the most damaging climate events in the world, with loss of life from some cyclones in the hundreds of thousands. Despite this, research on climate extremes in the region is substantially lacking compared to other parts of the world. To understand the narrative of how an extreme event in the region may change in the future, we consider Super Cyclone Amphan, which made landfall in May 2020, bringing storm surges of 2–4 m to coastlines of India and Bangladesh. Using the latest CMIP6 climate model projections, coupled with storm surge, hydrological, and socio‐economic models, we consider how the population exposure to a storm surge of Amphan's scale changes in the future. We vary future sea level rise and population changes consistent with projections out to 2100, but keep other factors constant. Both India and Bangladesh will be negatively impacted, with India showing >200% increased exposure to extreme storm surge flooding (>3 m) under a high emissions scenario and Bangladesh showing an increase in exposure of >80% for low‐level flooding (>0.1 m). It is only when we follow a low‐emission scenario, consistent with the 2°C Paris Agreement Goal, that we see no real change in Bangladesh's storm surge exposure, mainly due to the population and climate signals cancelling each other out. For India, even with this low‐emission scenario, increases in flood exposure are still substantial (>50%). While here we attribute only the storm surge flooding component of the event to climate change, we highlight that tropical cyclones are multifaceted, and damages are often an integration of physical and social components. We recommend that future climate risk assessments explicitly account for potential compounding factors.

Immersive storm surge flooding: Scale and risk perception in virtual reality

Immersive virtual reality (iVR) can enable users to experience phenomena at real-world scale. This attribute may be useful for communicating the risks of many natural hazards. Storm-surge is a flood hazard whose risk has proven challenging to communicate through traditional means, such as maps. When it comes to storm-surge flooding, iVR experiences have shown promise in increasing awareness of their danger. However, it is currently unclear whether iVR enhances risk perception over standard display methods, and how such experiences affect the interpretation of map products. To address these questions, we ran a between-participants experiment comparing the impact of display type (desktop versus iVR) on risk perception and spatial learning, using a custom-developed immersive simulation of storm-surge flooding. We measured perceived risk by having participants rate damage on a series of hypothetical storm-surge maps and making evacuation decisions in response to notional flooding. To understand if more accurately sized iVR representation led to better comprehension of flood heights, we measured participants’ ability to point to flood heights in a real environment. We found that iVR increases map damage-ratings and real-world height estimation accuracy, but that iVR leads participants to report that they would evacuate (and evacuate others) at higher water levels, indicating a disconnect between their understanding of environmental and bodily danger. We found that both desktop and iVR experiences aid map interpretation while iVR improves recall of flood heights in the real world. These results provide an avenue towards greater understanding of how iVR may be used for hazard-risk communication and conveying spatial information from immersive environments.

Integrated Runoff-Storm Surge Flood Hazard Mapping Associated with Tropical Cyclones in the Suburbs of La Paz, Baja California Sur, México

Floods are amongst the most frequent and destructive type of disaster, causing significant damage to communities. Globally, there is an increasing trend in the damage caused by floods generated by several factors. Flooding is characterized by the overflow of water onto dry land. Tropical cyclones generate floods due to excess water in rivers and streams and storm surges; however, the hazard of both phenomena is presented separately. In this research we present a methodology for the estimation of flood hazards related to tropical cyclones, integrating runoff and storm surge floods. As a case study, we selected the south-western suburbs of the city of La Paz, the capital of the state of Baja California Sur in northwest Mexico. The city has experienced in recent years an expansion of the urban area. In addition, there is an infrastructure of great importance such as the transpeninsular highway that connects the capital with the north of the state, as well as the international airport. Our results indicate that urban areas, agricultural lands, as well as the air force base, airport, and portions of the transpeninsular highway are in hazardous flood areas, making necessary to reduce the exposure and vulnerability to these tropical cyclone-related events. A resulting map was effective in defining those areas that would be exposed to flooding in the face of the impact of tropical cyclones and considering climate change scenarios, which represents an invaluable source of information for society and decision-makers for comprehensive risk management and disaster prevention.