Relative Flood Risk Research Articles

Increasing flood risk under climate change and social development in the Second Songhua River basin in Northeast China

Study regionSecond Songhua River basin (SSRB), Northeast China. Study focusAccurately assessing future flood risks is the premise and foundation of flood control and water resources management. At present, studies are still lacking in assessing future watershed flood risks that consider climate change and social development in Northeast China and the relative flood risk assessment framework. This study proposed an integrated flood assessment framework containing the AHP, entropy weight, and GCM downscaling methods, which was implemented in the SSRB, a typical watershed in Northeast China, to estimate future basin flood risks under climate change and social development. New hydrological insights for the regionThe flood risk in the SSRB will increase significantly in the mid-term (2051–2075) and long-term (2076–2100) future. The areas under the four scenarios with greater than high-risk levels will expand by 28.9 %, 105.6 %, 165.6 %, and 156.7 %, respectively, compared to the historical scenario. The newly added areas mainly located in the lower reaches. Precipitation changes are the primary reason for the future flood risks. The increased GDP under a higher forcing degree will also significantly increase the flood risk in the long-term future in the lower reaches. Based on these above findings, extreme precipitation forecasting and flood management in downstream areas in the basin need to be enhanced. Energy-saving and emission-reduction measures should be simultaneously implemented.

The benefits of coastal adaptation through conservation of foreshore vegetation

AbstractDue to rising sea levels and projected socio‐economic change, global coastal flood risk is expected to increase in the future. To reduce this increase in risk, one option is to reduce the probability or magnitude of the hazard through the implementation of structural, Nature‐based or hybrid adaptation measures. Nature‐based Solutions in coastal areas have the potential to reduce impacts of climate change and can provide a more sustainable and cost‐effective alternative to structural measures. In this paper, we present the first global scale assessment of the benefits of conserving foreshore vegetation as a means of adaptation to future projections of change in coastal flood risk. In doing so, we extend the current knowledge on the economic feasibility of implementing global scale Nature‐based Solutions. We show that globally foreshore vegetation can contribute to a large decrease in both absolute and relative flood risk (13% of present‐day and 8.5% of future conditions in 2080 of global flood risk). Although this study gives a first proxy of the flood risk reduction benefits of conserving foreshore vegetation at the global scale, it shows promising results for including Nature‐based and hybrid adaptation measures in coastal adaptation schemes.

A comparative flood damage and risk impact assessment of land use changes

Abstract. Sustainable flood risk management encompasses the implementation of nature-based solutions to mitigate flood risk. These measures include the establishment of land use types with a high (e.g., forest patches) or low (e.g., sealed surfaces) water retention and infiltration capacity at strategic locations in the catchment. This paper presents an approach for assessing the relative impact of such land use changes on economic flood damages and associated risk. This spatially explicit approach integrates a reference situation, a flood damage model, and a rainfall-runoff model considering runoff re-infiltration and propagation to determine relative flood risk mitigation or increment related to the implementation of land use change scenarios. The applicability of the framework is illustrated for a 4800 ha undulating catchment in the region of Flanders, Belgium, by assessing the afforestation of 187.5 ha (3.9 %), located mainly in the valleys, and sealing of 187.5 ha, situated mainly at higher elevations. These scenarios result in a risk reduction of 57 % (EUR 100 000) for the afforestation scenario and a risk increment of <1 % (EUR ∼ 500) for the sealing scenario.

Assessment of Flood Risk Map under Climate Change RCP8.5 Scenarios in Taiwan

Climate change has exerted a significant global impact in recent years, and extreme weather-related hazards and incidents have become the new normal. For Taiwan in particular, the corresponding increase in disaster risk threatens not only the environment but also the lives, safety, and property of people. This highlights the need to develop a methodology for mapping disaster risk under climate change and delineating those regions that are potentially high-risk areas requiring adaptation to a changing climate in the future. This study provides a framework of flood risk map assessment under the RCP8.5 scenario by using different spatial scales to integrate the projection climate data of high resolution, inundation potential maps, and indicator-based approach at the end of the 21st century in Taiwan. The reference period was 1979–2003, and the future projection period was 2075–2099. High-resolution climate data developed by dynamic downscaling of the MRI-JMA-AGCM model was used to assess extreme rainfall events. The flood risk maps were constructed using two different spatial scales: the township level and the 5 km × 5 km grid. As to hazard-vulnerability(H-V) maps, users can overlay maps of their choice—such as those for land use distribution, district planning, agricultural crop distribution, or industrial distribution. Mapping flood risk under climate change can support better informed decision-making and policy-making processes in planning and preparing to intervene and control flood risks. The elderly population distribution is applied as an exposure indicator in order to guide advance preparation of evacuation plans for high-risk areas. This study found that higher risk areas are distributed mainly in northern and southern parts of Taiwan and the hazard indicators significantly increase in the northern, north-eastern, and southern regions under the RCP8.5 scenario. Moreover, the near-riparian and coastal townships of central and southern Taiwan have higher vulnerability levels. Approximately 14% of townships have a higher risk level of flooding disaster and another 3% of townships will become higher risk. For higher-risk townships, adaptation measures or strategies are suggested to prioritize improving flood preparation and protecting people and property. Such a flood risk map can be a communication tool to effectively inform decision- makers, citizens, and stakeholders about the variability of flood risk under climate change. Such maps enable decision-makers and national spatial planners to compare the relative flood risk of individual townships countrywide in order to determine and prioritize risk adaptation areas for planning spatial development policies.

Research Design of Mobile Based Decision Support for Early Flood Warning System

Flooding has become one of the most rapidly growing types of natural disaster that has spread around the globe. It is is one of the major natural hazards in many countries and mostly affected in the low-lying or flood prone areas. In order to minimize loss of life and economic losses, a detailed and comprehensive decision making tool is necessary for both flood control planning and emergency service operations. In this paper, we demonstrate our research design for mobile based decision support of Flood Early Warning System (FEWS). We outlined four research objectives. Firstly, critical criteria for flood risk assessment will be identified and the second step will involve develop measurement model for relative flood risk using Geographic Information System (GIS), Multi Attribute Decision Making (MADM) and data mining technique. In the third objectives, the holistic architectural design is develop by incorporating the communication technology and other related ICT requirements for the mobile decision support. The fourth objective is to validate the mathematical model and architectural design. Case study approach is chosen in order to understand the flood event and validate the decision support model. Following well-defined procedures, flood maps were drawn based on the data collected from expert responses to a questionnaire, the field survey, satellite images, and documents from flood management agencies. It is anticipates that by integrating of mathematical model, GIS and mobile application in flood risk assessment could provide useful detailed information for flood risk management, evacuation, communication. The decision support design from this study is perhaps to improve the warning system and contribute to reduction of casualties.

Flood risk forecasting at weather to medium range incorporating weather model, topography, socio-economic information and land use exposure

Non-structural mitigation measures to the globally increasing flood events include forecast based alert generation. However, the extreme rainfall forecasts are associated with low hit rate, high false alarm, and spatiotemporal bias; which makes it difficult to rely on them. Further, the losses due to flood in a region not only depend on rainfall severity but also on topography, socioeconomic conditions and exposure of the region to floods. Here, we introduce a new concept of spatial flood risk mapping and forecasting at weather to medium range based on forecasted hazard, embedded with vulnerability (topographic and socioeconomic) and exposure information. We define hazard as the probability of extreme rainfall event during upcoming days given an available weather forecast for the same days. As hindcast is used for computation of probabilities, hazard contains prior information about the false alarm, hit rate and spatiotemporal bias of the forecast. Vulnerability is calculated by averaging the topographic and socioeconomic indicators, and exposure is calculated using a land use land cover map. Topographic vulnerability is computed with digital elevation model using Height Above the Nearest Drainage method, and Data Envelopment Analysis is performed to derive the socioeconomic vulnerability based on the demographic census data. For a specific region and a specific event, the relative flood risk maps are generated at an administrative level (e.g., district, subdistrict or village level for India) and the high-risk areas can be identified from those maps for mitigation. The methodology is demonstrated for a very recent extremely severe flood event that happened in Kerala, India in August 2018. It is evident from the results that the high-risk areas forecasted well in advance (as high lead time as 15 days) match fairly well with the areas, which suffered maximum losses because of direct flood.

Applying fuzzy logic to open data for sustainable development decision-making: a case study of the planned city Amaravati

The Indian State of Andhra Pradesh is in the process of designing and constructing a planned capital city on the southern banks of the Krishna River at Amaravati. This region will see a significant increase in urban land cover and impervious surface area (ISA) under the 2050 draft perspective plan from the Andhra Pradesh Capital Region Development Authority. As the city central zone sits on the former floodplain of the Krishna River and is subject to concentrated rainfall during monsoon seasons—this increase in ISA risks increasing flood risk through preventing infiltration of storm water and causing increased peak storm water flow (NRSC 2014). The State has announced plans for a “zero-flooding city” through implementation of technologies including green roofs, porous pavement, and detention ponds (ADC 2017). This study aims to facilitate these efforts through mapping of present and future land usage, regional flood risk, and environmental services utilizing open-source data in order to maximize efficiency of installed green infrastructure and minimize future flood damages. A map of relative soil infiltration capacity was created through fuzzy overlay of sand percentage, clay percentage, and bulk density at several depths. Relative flood risk maps for both present-day land cover and a 2050 scenario were developed using several factors: elevation, flow accumulation, surface runoff, and soil properties. A novel Relative Environmental Services Provided Index is proposed here to in order to encourage cost-effective and ecologically sound development through composite visualization of carbon storage, greenery, runoff coefficients, and soil flood prevention.

A Flood Risk Assessment Model for Companies and Criteria for Governmental Decision-Making to Minimize Hazards

Flood risks in the industrial sector and economic damages are increasing because of climate change. In addition to changes in precipitation patterns due to climate change; factors that increase flood damage include infrastructure deterioration and lack of storage facilities. Therefore; it is necessary for companies and the government to actively establish flood management policies. However; no evaluation method is currently available to determine which items should be invested in first by small and medium-sized enterprises that have limited finances. Because the government should make comprehensive and fair decisions; the purpose of this study is to propose priority investment risk items and an assessment method to decide which companies should be invested in first in flood risk management due to climate change. The multispatial scale of the method takes both the location and characteristics of the company into account. Future climate change scenarios were used to evaluate the changing patterns of flood risks. We developed the relative Flood Risk Assessment for Company (FRAC model) methodology to support the government’s policymaking. This method was applied to four companies belonging to four different industries and three risk items were derived that are likely to harm the company owing to flooding.

지표평균법 및 PROMETHEE 결과 종합에 의한 홍수위험도 분석

This study has performed the flood risk assessment in order to provide preliminary information in the establishment of flood risk management and damage reduction strategies. The twelve representative flood risk factors were carefully selected for the flood risk assessment based on the P-S-R(Pressure-State-Response) classification system, and spatially constructed for the nationwide 812 standard watersheds of the national water resource unit map. The relative flood risk was estimated by the two methods; the one is a FRI(Flood Risk Index) by averaging the three flooding indexes such as PI(Pressure Index), SI(State Index), and RI(Response Index) by each four flood risk factor classified from the twelve factors, and the other is the PROMETHEE(Preference Ranking Organization METHod for Enrichment Evaluation) by estimating a complete outranking from the preference matrix analysis for the twelve alternatives. This study has newly presented the final flood risk determined by the higher risk value of two flood risk assessment results, which is expected to be used to identify flooding risk areas in terms of the integrated flood risk management.

Estimation of flood risk index considering the regional flood characteristics: a case of South Korea

Global warming is increasing the variability of climate change and intensifying hydrologic cycle components including precipitation, infiltration, evapotranspiration, and runoff. These changes increase the chance of more severe and frequent natural conditions, and limit ecosystem function and human activities. Adaptation to climate change requires assessment of the potential disaster risk. The objectives of this study were to estimate the flood risk index (FRI) considering regional flood characteristics at the national level and to prioritize the factors affecting flood risk through principal component analysis. FRI was estimated based on the Delphi survey results from 50 water resources experts in South Korea. The potential risk analysis was conducted for 229 local governments in South Korea. The results showed that natural and social factors were more influential flood risk factors to South Korea than administrative and economic and facility factors. Specifically, natural, social, administrative and economic, and facility factors were, respectively, highest at Jindo-Gun in Jennam-Do, Gumi-Si in Kyongsanbuk-Do, Dong-Gu in Incheon-Si, and Suwon-Si, Kyonggi-Do. Overall, the highest FRI is shown in Anyang-Si, Kyongggi-Do. The spatial distribution of the FRI was high in the southeastern coastal region and basins of the two biggest rivers in South Korea, and normalized flood frequency followed spatial patterns similar to FRIs. This study provided information on the relative flood risk index among administrative units for investment prioritization in flood risk management. In this regard, the suggested FRI is expected to significantly contribute to methodical and economic improvements in budget allocations for flood risk management.

Annualised risk analysis approach to recommend appropriate level of flood control: application to Swannanoa river watershed

AbstractThis study presents an analysis approach using an existing Monte Carlo (MC) flood risk framework to compare annualised risk reductions from flood control alternatives targeting various recurrence interval events. The annualised risk approach is demonstrated by analysing the relative flood risk mitigation benefits of flood proofing in Swannanoa watershed, North Carolina. Using the MC framework, 54 design flows are sampled from the flow distribution and used to drive a graphics card based two‐dimensional flood model. The computed flood depths are used to create flood damage frequency and annualised risk curves. It was hypothesised that flood proofing for a higher probability event would result in a greater relative level of damage reduction for lower cost compared with the traditional use of a 1% annual exceedance flood event. The MC framework was used to test the hypothesis by producing a distribution of annualised risk over various return periods. Confirming the hypothesis, the 12% flood event was found to have the highest annualised risk for the case study in this paper. Simulations were executed to determine the relative costs and benefits of the 12% flood proofing (alternate case) and 1% flood proofing (base case) alternatives. The results showed that the base case reduced the expected annual damage (EAD) by 98.9% compared with the status quo. The alternate case reduced the EAD by 80.4% compared with the status quo. Comparing estimated annual implementation cost with flood damage reductions, annually, for every dollar spent on flood proofing, the 12% design resulted in twice the reduction in flood damages compared with the 1% design. This preliminary study thus confirms the potential of an alternative analysis approach that may be applied for identifying desired flood control level based on flood risk mitigation potential.

Spatially-explicit assessment of flood risk caused by climate change in South Korea

Identifying spatially-explicit risk is essential for efficient flood management with limited resources and budgets. We investigated national-scale relative flood risk for 139 sub-basins in South Korea under current and future climate conditions. A non-parametric index method was employed to calculate relative flood risk based on a sensitivity index, an exposure index, and an adaptive capacity index for each sub-basin. A dynamically downscaled climate simulation based on the A2 Greenhouse Gas (GHG) emission scenario, provided by the Korean Meteorological Research Institute (METRI), was used to examine possible change in flood risk. The estimated flood risk generally agreed with historical flood damage. The highly vulnerable sub-basins had high exposure indices, reflecting frequent heavy rainfall, as well as high sensitivity indices due to dense population at low elevation. Although rainfall intensity and frequency is likely to increase under the A2 GHG emission scenario, the spatial pattern of relative flood risk did not change remarkably. Our results indicate that reducing flood sensitivity levels and enhancing the adaptive capacity in vulnerable regions will be critical aspects of climate change preparation in South Korea.

Integrated application of the analytic hierarchy process and the geographic information system for flood risk assessment and flood plain management in Taiwan

Flooding is one of the major natural hazards in Taiwan, and most of the low-lying areas in Taiwan are flood-prone areas. In order to minimize loss of life and economic losses, a detailed and comprehensive decision-making tool is necessary for both flood control planning and emergency service operations. The objectives of this research were (i) to develop a hierarchical structure through the analytic hierarchy process (AHP) to provide preferred options for flood risk analysis, (ii) to map the relative flood risk using the geographic information system (GIS), and (iii) to integrate these two methodologies and apply them to one urban and one semi-rural area in central Taiwan. Fushin Township and the floodplain of Fazih River (1 km on either side of the channel) in Taichung City were selected for this study. In this paper, the flood risk is defined as the relative flood risk due to broken dikes or the failure of stormwater drainage systems. Seven factors were considered in relation to the failure of stormwater drainage, and five to that of broken dikes. Following well-defined procedures, flood maps were drawn based on the data collected from expert responses to a questionnaire, the field survey, satellite images, and documents from flood management agencies. The relative values of flood risk are presented using a 200-m grid for the two study areas. It is concluded that integration of AHP and GIS in flood risk assessment can provide useful detailed information for flood risk management, and the method can be easily applied to most areas in Taiwan where required data sets are readily available.