Local Flood Risk Research Articles

Tropical Cyclone Storm Surge‐Based Flood Risk Assessment Under Combined Scenarios of High Tides and Sea‐Level Rise: A Case Study of Hainan Island, China

AbstractIn the context of climate change, coastal flood risk is intensifying globally, particularly in China, where intricate coastlines and frequent tropical cyclones make storm surges a major concern. Despite local government's efforts to initiate coastal monitoring networks and qualitative risk guidelines, there remains a gap in detailed and efficient quantitative assessments for combinations of multiple sea‐level components. To address this, we develop the Tropical Cyclone Storm Surge‐based Flood Risk Assessment under Combined Scenarios (TCSoS‐FRACS). This framework integrates impacts of storm surges, high tides, and sea‐level rise using a hybrid of statistical and dynamic models to balance reliability and efficiency. By combining hazard, exposure, and vulnerability, it incorporates economic and demographic factors for a deeper understanding of risk composition. Applying TCSoS‐FRACS to Hainan Island reveals that the combined effects of storm surges, high tides, and sea‐level rise significantly amplify local coastal flood risk, increasing economic losses to 4.27–5.90 times and affected populations to 4.96–6.23 times. Additionally, transitioning from Fossil‐fueled Development (SSP5‐8.5) to Sustainability (SSP1‐1.9) can reduce the risk increase by approximately half. The equivalence in flood hazard between current high tides and future sea level under a sustainable scenario boosts confidence in climate change adaptation efforts. However, coastal cities with low hazard but high exposure need heightened vigilance in flood defense, as future risk could escalate sharply. Our study provides new insights into coastal flood risk on Hainan Island and other regions with similar profiles, offering a transferable and efficient tool for disaster risk management and aiding in regional sustainable development.

Developing an Audit Framework for Local Flood Risk Management Strategies: Is Increasing Surface Water Flood Risk in England Being Adequately Managed?

Developing an Audit Framework for Local Flood Risk Management Strategies: Is Increasing Surface Water Flood Risk in England Being Adequately Managed?

Mapping Tools for Flood Risk Rescue and Assistance Management

The assessment of vulnerability to the danger of flooding, with a focus on the need for rescue and assistance from the population, is still in an exploratory scientific phase. The main objective of this research is to propose a methodology based on the issues of rescue and assistance in the face of the risk of floods and to provide a tool for its management. A series of maps is presented, indicating those territorial elements that require rescue and surveillance in a prioritized manner in a visual and accessible way for public administration. Four methodological cartographic proposals have been designed as follows: (1) a map of territory sectors with special rescue needs (dependent population and/or buildings without shelter); a map of the impact on transportation infrastructure and vulnerable areas of buildings (2); a map of vulnerability to possible disorder and looting caused by flooding events (3); and a map of the increase in the cost of deployment for rescue and assistance systems (4). As an experimental zone to test the effectiveness of these proposals, a peri-urban area of the municipality of Málaga (Spain) is chosen, which has an extensive history of severe floods. The results confirm the applied and preventive nature of the tool, which can be incorporated into flood risk management plans and local flood risk action plans developed by public administrations. The main finding of the research is the technical advancement that comes with a precise understanding of vulnerability and its resulting issues for better flood risk management.

A participatory systems dynamic modelling approach to understanding flood systems in a coastal community in Cameroon

In the face of increasing flood risks and the need for effective management both at national and local levels, this study highlights a participatory approach that transcends conventional stakeholder consultation but delves into drawing insights through conceptual models that unveil the potential of the Participatory System Dynamic Modelling approach to mitigate flood risks, even at the grassroots level effectively. Through active stakeholder engagement, the study focuses on identifying and analysing the intricate interdependencies and feedback loops within the Limbe flood risk management system that are crucial for recommending comprehensive and actionable flood risk mitigation strategies for Limbe's cross-sectoral dynamics. By including flood experts and community stakeholders in the conceptual model construction, the study utilises an evaluative framework that accounts for system processes and outcomes, ensuring a holistic understanding of the flood risk system, considering scientific knowledge and real-life experiences. The findings underscore the value of participatory modelling techniques in facilitating the identification and prioritisation of intervention options by diverse stakeholders, thereby promoting active engagement in local flood risk management, a vital step in addressing the escalating challenges posed by climate change and natural disasters.

Ecosysem-based approach to local flood risk management in Ogun State, Nigeria: Knowledge, and pathway to Actualisation

Flooding continues to ravage communities and leave societies driven by quest towards a more likely solution to flood threats. The need to accommodate both the provision of fundamental human needs and the core values and functions of the natural environment, for instance, controlling floods, puts emphasis on sustainability and illustrates the worth of ecosystem-based approach to flood risk management in locations inhabited by almost half a million people in danger of flooding. This study aims to assess the awareness of ecosystem services in the Ogun State of Nigeria and how a sustainable appropriation of the natural resources can aid local flood risk mitigation and control. The study employed a mixed-method approach through a thorough literature search to gather secondary data and a semi-structured questionnaire to source primary data from a population of 1483 participants in the study area. From the analyses, a considerable proportion of the participants (∼70%) possess a profound knowledge of flood risk and are aware of local flood abatement and ecosystem services. Based on all measured variables, only less than half of the sampled respondents identified with the idea of ecosystem, although just about 43.6% of the sampled population failed to grasp that exploring more efficient ways of using natural resources can aid in tackling flooding in the study area. With this outcome in mind, the area under study can only attain a holistic flood risk management framework by making ecosystem-based flood risk management the centrepiece of local flood risk mitigation policy and practice. This research suggests a new angle to help incorporate ecosystem service into local FRM, fortify the resilience of communities and adapt indigenous methods and assets for flood risk mitigation economy and regulation.

Encouraging planting in urban front gardens: a focus group study.

Encouraging planting in front gardens offers mental and physical health benefits, as well as positive local environmental impacts such as reducing flood risk and improving air quality. However, urban front garden greenery has reduced in recent years. We aimed to explore adults' views regarding planting greenery in front gardens, barriers and facilitators, and their understanding of health and environmental impacts, to identify appropriate intervention mechanisms for behaviour change. We carried out five online focus groups with 20 participants aged 20-64 in England, purposively sampled for variation according to age, gender, home ownership, income, ethnicity and residing in an urban or suburban area. We audio recorded each focus group, transcribed it verbatim and analysed transcripts using thematic analysis. Front gardening was a relaxing activity that provided benefits including increased wellbeing, fresh air and vitamin D. Planting in front gardens depended heavily on available time and space, garden orientation, local security and the weather. Front gardens could be a place for social interaction. Participants tended to prioritise neatness and tidiness over greenery. Lack of knowledge and low self-efficacy were key barriers. There was little awareness of the environmental benefits of front garden greenery; however, reducing flood risk and encouraging biodiversity were viewed positively. Initiatives to encourage front garden planting should focus on plants that require little knowledge to acquire and care for, are suitable to the local environmental conditions and with a visual impact of neatness and bright colour. Campaigns should draw attention to local flood risk reduction and increasing biodiversity, in addition to personal health benefits.

A place-based risk appraisal model for exploring residents' attitudes toward nature-based solutions to flood risks.

Nature-based solutions (NBS) have gained popularity as a sustainable and effective way of dealing with increasing flood risks. One of the key factors that often hinders the successful implementation of NBS is residents' opposition to their implementation. In this study, we argue that the place where a hazard exists should be considered a critical contextual factor alongside flood risk appraisals and perceptions of NBS themselves. We have developed a theoretical framework-the "Place-based Risk Appraisal Model (PRAM)"-that draws on constructs inspired by theories of place and risk perception. A citizen survey (n=304) was conducted in five municipalities in Saxony-Anhalt, Germany, where dike relocation and floodplain restoration projects have been conducted along the Elbe River. Structural equation modeling was adopted to test the PRAM. Attitudes toward the projects were assessed in terms of "perceived risk-reduction effectiveness" and "supportive attitude." With regard to risk-related constructs, well-communicated information and perceived co-benefits were consistently positive factors for both perceived risk-reduction effectiveness and supportive attitude. Trust in local flood risk management was a positive and threat appraisal a negative predictor of perceived risk-reduction effectiveness affecting "supportive attitude" only through "perceived risk-reduction effectiveness." Regarding place attachment constructs, place identity was a negative predictor of a supportive attitude. The study emphasizes that risk appraisal, pluralities of place contexts to each individual, and their relations are key for determining attitudes toward NBS. Understanding these influencing factors and their interrelationships enables us to provide theory- and evidence-based recommendations for the effective realization of NBS.

Flood risk research for improving flood risk outcomes

Flood risk research for improving flood risk outcomes

Decision-support for land reclamation location and design choices in the Maldives

Land reclamation in the Maldives is widespread. Current land reclamation practices, however, lack a systematic approach to anticipate sea-level rise and do not account for local flood risk differences to inform location and design choices. To address these limitations, this paper applies two decision-support tools: a hazard threshold analysis, and a cost-benefit analysis. Both tools produce site-specific estimates of land elevations or flood defence heights but do so for different goals. The hazard threshold analysis identifies hazard-based solutions that meet an acceptable flood probability for an intended lifespan without follow-up actions by reliability optimisation. The cost-benefit analysis identifies risk-based solutions using dynamic programming. We apply both tools to two land reclamation sites, a newly reclaimed airport island and a land extension of an inhabited island, in the Maldives. We find that total hazard-based heights for long-term planning horizons are highly uncertain, with local height differences of up to 1.9 m across sea-level rise scenarios by 2100. Risk-based Island elevations, in contrast, differ much less across scenarios, offering a practical advantage for decision-making. However, land reclamation choices on location, land elevation and investment in flood protection are not only driven by hazard-related aspects, such as reef characteristics, swell exposure, and sea-level rise, but also by estimates of exposed assets, reclamation, and flood protection costs. Taken together, the two decision-support tools are helpful for improving adaptation decisions and are also applicable in other small island regions.

Does federal flood hazard mitigation assistance affect community rating system participation?

With the inexorable march of climate change, increased flooding is inevitable. Understanding the feedback between federal flood mitigation policies and the ways in which local governments build flood resilience is a significant gap in the literature. In particular, the effect that federal flood mitigation grants have on the intensity of local flood mitigation is nonexistent. This work measures flood risk mitigation by using the level of participation in FEMA's Community Rating System (CRS). Communities that participate in the CRS and undertake mitigation are awarded points; more points imply a higher level of participation. Since its inception in 1990, CRS communities have received considerably more federal pre-disaster flood mitigation grants compared to non-CRS communities. This study assesses the effect of federal pre-disaster flood mitigation grants on the level of participation in the CRS program. We use data on Hazard Mitigation Assistance programs and CRS participation data between 2010 and 2015. We link these data to flood risk and socioeconomic information. Our results indicate (i) federal pre-disaster flood mitigation grants do not appear to significantly influence the level of CRS participation, (ii) the effect of flood risk and socioeconomic factors on the level of CRS participation are mixed, and (iii) the current level of CRS participation is influenced by the previous level of CRS participation, which is not tied to federal pre-disaster flood mitigation grant. These findings add to the growing discussions on the drivers and barriers of local flood risk mitigation.

Innovative Vulnerability and Risk Assessment of Urban Areas against Flood Events: Prognosis of Structural Damage with a New Approach Considering Flow Velocity

The floods in 2002 and 2013, as well as the recent flood of 2021, caused billions Euros worth of property damage in Germany. The aim of the project Innovative Vulnerability and Risk Assessment of Urban Areas against Flood Events (INNOVARU) involved the development of a practicable flood damage model that enables realistic damage statements for the residential building stock. In addition to the determination of local flood risks, it also takes into account the vulnerability of individual buildings and allows for the prognosis of structural damage. In this paper, we discuss an improved method for the prognosis of structural damage due to flood impact. Detailed correlations between inundation level and flow velocities depending on the vulnerability of the building types, as well as the number of storeys, are considered. Because reliable damage data from events with high flow velocities were not available, an innovative approach was adopted to cover a wide range of flow velocities. The proposed approach combines comprehensive damage data collected after the 2002 flood in Germany with damage data of the 2011 Tohoku earthquake tsunami in Japan. The application of the developed methods enables a reliable reinterpretation of the structural damage caused by the August flood of 2002 in six study areas in the Free State of Saxony.

Variation in root morphology amongst tree species influences soil hydraulic conductivity and macroporosity

Natural approaches to flood risk management are gaining interest as sustainable flood mitigation options. Targeted tree planting has the potential to reduce local flood risk, however attention is generally focused on the hydrological impacts of catchment afforestation linked to generic tree features, whilst the species-specific impacts of trees on soil hydrology remain poorly understood. This study compared effects of different tree species on soil hydraulic properties. Monocultures of Alnus glutinosa (common alder), Fraxinus excelsior (European ash), Fagus sylvatica (European beech), Betula pendula (silver birch), Castanea sativa (sweet chestnut), Quercus robur (English oak) and Acer pseudoplatanus (sycamore maple) were used to determine effects of tree species identity on soil hydraulic properties (near-saturated K and soil water retention) in a sandy loam soil, North Wales, United Kingdom. The interaction of F. excelsior root properties and soil class on hydraulic conductivity was also examined in four different soils (Rendzic Leptosol, Haplic Luvisol, Dystric Fluvic Cambisol and Dystric Gleysol) across England and Wales. Fine root biomass (FRB) and morphological characteristics were determined at three depths (0–0.1, 0.1–0.2 and 0.2–0.3 m) and complemented by in situ surface measurement of soil hydraulic conductivity. Root morphological traits were closely associated with species identity and pore-size distribution, and FRB was strongly correlated with soil hydraulic conductivity (R2 = 0.64 for 0–0.1 m depth FRB; R2 = 0.69 for 0.1–0.2 m depth FRB). Fine root biomass of F. excelsior was sixfold greater than C. sativa (p < 0.001), and the frequency of 0.01 mm radius soil pores under F. excelsior was twice that of Q. robur. Near-saturated hydraulic conductivity under F. excelsior was 7.91 ± 1.23 cm day−1, double the mean rate of the other species. Soil classification did not significantly influence FRB (p = 0.056) or near-saturated hydraulic conductivity (p = 0.076) in the 0.0–0.1 m depth soil, but soil water retention varied with depth. Species-specific traits of trees should be considered in landscape design to maximise the local hydrological benefits of trees.

A methodological approach for mapping and analysing cascading effects of flooding events

Current local or regional flood risk assessments, as required by the EU flood risk directive, rarely account for cascading effects due to interdependencies between critical infrastructures. However, it is essential to consider these effects, as they may severely impact areas outside the immediate flood risk area. The main purpose is to present and problematise a method (AB-CEM) for mapping and analysing cascading effects due to floods, aiming at also being relevant for other spatially widespread hazards. The method development and the pilot study, in Sweden, reveal that there is a prominent practical need for methods for mapping and analysing critical infrastructure interdependencies and cascading effects. Another key finding is that the method process and its results can serve as an important basis for decision-making about proactive and reactive efforts related to geographically extensive hazards. We further conclude that there is a recurring problem regarding sensitive and secret data. More specifically, the conflicting interests of information availability and information security concerning critical infrastructures, which needs to be resolved at the national level and communicated through clear guidelines. The method is a much-needed step towards accounting for cascading effects of floods in practice.

Runoff prediction of Surma basin by curve number (CN) method using ARC-GIS and HEC-RAS

Bangladesh being a low-lying country is affected by floods easily that turns the Sylhet city more vulnerable to floods due to improper management of stormwater and failure in estimating runoff volume of Surma River. For this, CN value of the city area, the direct runoff of the area and the peak discharge value for different return periods were calculated. Meanwhile, geometric data and peak discharge were imported into HEC-RAS software to obtain flood depth and flood extend. Finally, an HEC-GeoRAS simulation resulted in a floodplain map. The inundation area found from the floodplain map covers 6.34% of the total study area for 2 years return period. To continue, 6.37%, 6.42%, 6.55%, 6.70% and 6.88% for 5 years, 10 years, 25 years, 50 years and 100 years return period respectively. These maps and relevant discharge data may help to understand the local flood risks and take up cost-effective measures.

Economic evaluation of sea-level rise adaptation strongly influenced by hydrodynamic feedbacks

Coastal communities rely on levees and seawalls as critical protection against sea-level rise; in the United States alone, $300 billion in shoreline armoring costs are forecast by 2100. However, despite the local flood risk reduction benefits, these structures can exacerbate flooding and associated damages along other parts of the shoreline-particularly in coastal bays and estuaries, where nearly 500 million people globally are at risk from sea-level rise. The magnitude and spatial distribution of the economic impact of this dynamic, however, are poorly understood. Here we combine hydrodynamic and economic models to assess the extent of both local and regional flooding and damages expected from a range of shoreline protection and sea-level rise scenarios in San Francisco Bay, California. We find that protection of individual shoreline segments (5 to 75 km) can increase flooding in other areas by as much as 36 million m3 and damages by $723 million for a single flood event and in some cases can even cause regional flood damages that exceed the local damages prevented from protection. We also demonstrate that strategic flooding of certain shoreline segments, such as those with gradually sloping baylands and space for water storage, can help alleviate flooding and damages along other stretches of the coastline. By matching the scale of the economic assessment to the scale of the threat, we reveal the previously uncounted costs associated with uncoordinated adaptation actions and demonstrate that a regional planning perspective is essential for reducing shared risk and wisely spending adaptation resources in coastal bays.

Participatory Approaches to Urban Flood Risk Mitigation and Adaptation Strategies Projects: A Scoping Review of the Global South Evidence

Participatory approaches to urban flood risk adaptation initiatives have been prominent amongst developed countries, particularly in Europe, since the 2000s and are now steadily on the rise in the Global South. In this article we focus on how international examples of community-based participatory research and practice have managed flooding risk mitigation and adaptation strategies, specifically in the Global South. While top-down resistance-based approaches that include infrastructure, technology, laws and regulations offer invaluable information for urban planners and policy-makers they however fall short on revealing the perceptions and behaviours that shape individual, household and community adaptation decision-making process. In addition, these top-down approaches tend to take a long-term view of change with new programmes or policies, implemented over time, failing to tackle current challenges. The aim of this scoping review is therefore to map out the key concepts underpinning this research area and the main sources of evidence addressing community-based flooding monitoring, mitigation and adaptation strategies to uncover practices that facilitate participatory models of working between researchers, urban developers/designers, government institutions, and local communities. Finally, this evidence-based synthesis serves as background to the presentation of a Mexican case-study in which a community-based participatory approach is employed to support a co-production process for the identification of local flood risk management options.

Identification of the inter-basin water diversion project-effected local flood risk factor by using the fishbone-diagram method

When carrying out the inter-basin water diversion project, we must face problems such as the long river routing distance and complex hydro-meteorological conditions along the main channel. Under the condition of the unchangeable standard of the designed rainstorm, the changes of the underlying surface could inflect the designed flood. As a result, the drainage channel is not as consistent as the designed condition, therefore the flood discharge condition in the upper and lower sub-reaches changes, and the actual flow capacity of the hydraulic structure is reduced compared with the designed conditions. The above-mentioned situations could cause risk event of the rising of designed flood level in the left bank and will cause local flood risk, and also cause corresponding economic losses and social impacts. In this study, for the first time, the fishbone-diagram method is applied to identify the local flood risk factors of the inter-basin water diversion project. By using this method, the changes of characteristic values of watershed above cross section, villages, factories or other buildings at the outlet location of the drainage structures etc. are identified as the local flood risk factors, and there are mainly eight types of local flood risk factors which can be taken into consideration when selecting engineering and non-engineering measures to reduce or eliminate the risk factors. PACS: J0101

‘Learning for resilience’ as the climate changes: discussing flooding, adaptation and agency with children

Climate change scenarios project higher flood risk, so knowing how households can increase socio-ecological resilience is essential. Children rarely feature in UK policy guidance about how households prepare for floods, and research is limited about children’s roles in local resilience building. Using a participatory action research, child-centred methodology we explored (7-9year old) children’s knowledge, skills and dispositions in discussions about flooding, suggesting processes for effectively engaging them in Learning for Resilience (LfR). Results suggest children have existing knowledge, skills and dispositions concerning local and international flood risk originating from various sources. They displayed cross-cultural learning, embryonic systems-thinking, and understandings of theirs and others’ agency, including adults’ reasons for un-preparedness, revealing awareness of risk underestimation and deferral/denial of risk. The paper offers framing of a new taxonomy for young children’s significant ‘LfR’ and seven ‘top tips’ to facilitate, design and implement learning strategies with children around environmental risk, in the UK and internationally, in climate change contexts.

The Effect of Storm Direction on Flood Frequency Analysis

AbstractStorm direction modulates a hydrograph's magnitude and duration, thus having a potentially large effect on local flood risk. However, how changes in the preferential storm direction affect the probability distribution of peak flows remains unknown. We address this question with a novel Monte Carlo approach where stochastically transposed storms drive hydrologic simulations over medium and mesoscale watersheds in the Midwestern United States. Systematic rotations of these watersheds are used to emulate changes in the preferential storm direction. We found that the peak flow distribution impacts are scale‐dependent, with larger changes observed in the mesoscale watershed than in the medium‐scale watershed. We attribute this to the high diversity of storm patterns and the storms' scale relative to watershed size. This study highlights the potential of the proposed stochastic framework to address fundamental questions about hydrologic extremes when our ability to observe these events in nature is hindered by technical constraints and short time records.

Assessment of local outburst flood risk from successive landslides: Case study of Baige landslide-dammed lake, upper Jinsha river, eastern Tibet

Two large landslides in October and November 2018 sequentially dammed the Jinsha river at Baige village, eastern Tibet, China. Subsequently, breaching of each dam induced massive outburst floods that posed a severe threat to downstream cities and infrastructure. Field investigation indicates volumes of the first and second landslide dam are about 24.5 × 106 m3 and 8.53 × 106 m3, respectively. However, the peak discharge of the flood generated from the second landslide (3.1 × 104 m3/s) was significantly larger than that from the first (1.0 × 104 m3/s). The second peak discharge would have been 5.15 × 104 m3/s if the dam breached naturally. In this study, we developed two geometry parameters: effective dam height He (elevation difference between overtopping level and river bottom) and a narrowing number distribution Nr(H) (measures the degree to which a river section is occupied by landslide materials to elevation H) which represents river section narrowing effects of successive landslides. Using numerical simulations, we show that He dominates peak discharge, and it has a linear relationship with peak discharge with slope of 1009.4 m2/s. Furthermore, the dam includes two sub-areas: a higher part (SB-1) and a lower part (SB-2). Two floods only eroded SB-2. However, breaching of SB-1 and breached SB-2 still narrowed the river. The narrowing effects of the first and second breached dam on the river channel are around 0.35 and 0.5, respectively. Spillway and landslide runup deposits increased the local flood risk by narrowing and lifting the local river section; the first landslide promoted the second landslide, which occupied the same area and forms a dam with high He value. Consequently, a more catastrophic flood could be triggered by a small subsequent landslide. Spatial superposition phenomenon of successive landslides increased the local flood risk. This research quantitatively analyzed the influence of the geometry of dam induced by successive landslides on the process of outburst floods and the risk.