High Flood Risk Research Articles

A bootstrap approach for the parameter uncertainty of an urban-specific rainfall-runoff model

The predictions made using rainfall-runoff models are inherently uncertain and it is important to recognize and account for this uncertainty, especially in urban watersheds due to the high flood risk in these areas. Recent studies on hydrological model uncertainty mostly refer to the identification of model parameter uncertainty. However, such studies are somewhat limited using the bootstrap approach, a nonparametric method which makes less prior assumptions on the model structure and thus is more flexible. Hence, a residual-based bootstrap approach associated with the SCE-UA global optimization algorithm is demonstrated in this study for the analysis of calibrated parameter uncertainty and its subsequent effect on the model simulation of an urban-specific rainfall-runoff model, urban storage function (USF) model, under two different data scenarios of individual event-based and whole data-based scenarios. Initially, the parameter uncertainty was expressed by estimating the confidence interval (CI) of the USF model parameters obtained from bootstrapping and then the parameters from the highest to the lowest uncertainties were derived by utilizing two newly proposed parameter uncertainty indices which can make the best use of CI. Moreover, investigations on the effect of calibrated parameter uncertainty on model simulations revealed that the model was able to bracket most of the observations within the prediction range of considered scenarios. This further indicates that the residual-based bootstrap approach along with the SCE-UA method reasonably well predicted the uncertainty range of the USF model. For a better understanding of simulation uncertainty, we defined and demonstrated two model simulation uncertainty indices and these indices could be useful in future studies to analyze the simulation uncertainty of different rainfall-runoff models in the watersheds worldwide.

Climate-induced hydrological impact mitigated by a high-density reservoir network in the Poyang Lake Basin

The Poyang Lake Basin (PLB) is expected to see more precipitation and higher temperature by 2050. Due to climate change, it is advisable to identify the vulnerable area and to investigate if the local reservoir network of hundreds of larger reservoirs and thousands of smaller reservoirs can effectively mitigate the climate-induced hydrologic variation. Therefore, the local high-density reservoir network is integrated into a distributed hydrologic model (HMS) through a fully coupled reservoir module. We then apply the extended HMS in a one-way coupled mode to the bias corrected Coordinated Regional Downscaling Experiment in East Asia (CORDEX-EA) regional climate simulations under two Representative Concentration Pathways – RCP4.5 and RCP8.5. Results indicate that climate change poses new challenges to water resources management for the PLB, with a likely decrease of water availability in the dry season but an increase of water availability, flood magnitude and flood frequency in the flood season till 2049. The local reservoir network can mitigate climate impacts by displacing excessive water resources in the flood season to the dry season and mitigating floods across the basin. Despite that, much of the southern basin is likely to see a higher risk of water shortage in the dry season, while most of the northern basin is expected to see a higher flood risk. The approach and findings are expected to improve the understanding of the role of reservoirs in the context of climate change, and provide implications for water resources management and climate change adaptation strategies on a regional scale.

A geospatial approach to flash flood hazard mapping in the city of Warangal, Telangana, India

Abstract Dense urbanization leading to uncontrolled transformations within settlements result in flash flooding with overflowing drains leading to a greater inconvenience for the public and damage to private properties. Hence mapping of flash floods would be useful in identifying the high-risk flood zones for disaster response and urban services, during emergencies with rainfall events of high intensity. This article aims to prepare a flood hazard map of Warangal Municipal Corporation (WMC) in Telangana State, India. WMC is chronically affected due to a rise in water levels resulting in flash floods, with an increase in encroachments. The factors considered in this study are rainfall (curve number), surface slope and surface roughness, type of soil, and distance to main channel, drainage density, and land use cover. To decide the relative weight of the impact of each flood causative factors an Analytical Hierarchical Process (AHP) was used. Accordingly, a composite Flood Hazard Index (FHI) has been derived by using the multiple-criteria decision-making tools by integrating these into a Geographical Information System (GIS). The Soil and Water Assessment Tool (SWAT) in Quantum GIS (QGIS), which is a hydrological model, was used to evaluate the projection of streamflow over the water basin and model parameters were optimized using water balance equations during calibration and validation periods.

A Study on Temporary Shelter Areas Using Pedestrian Networks in Coastal Cities

Kim, J.O. and Lee, J.K., 2019. A study on temporary shelter areas using pedestrian networks in coastal cities. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 421-425. Coconut Creek (Florida), ISSN 0749-0208.This study aims to analyze service area of shelter in order to plan the evacuation route using a pedestrian-level network in coastal cities. We proposed the process of shelter service area demarcation, which is applied various scenarios for flood inundation risk map, considers the characteristics of refugees such as the general public and the elderly. To solve the problem, the coastal flood maps were constructed to take into account the rise in sea level due to climate change. By using the GIS(Geographic Information System), we calculated the slop of the road by adding elevation to the link of pedestrian-level network, applied differently the walking time according to the slope. A case study was conducted to demonstrate the application of the service area for flood emergency shelters of coastal cities in Republic of Korea. The service area of the study, which reflects the elevation, the condition of evacuees, the accessibility and the flood map, was able to arrive at the shelter in a short time avoiding the high risk of flooding.

FLOOD IMPACT-BASED FORECASTING FOR EARLY WARNING AND EARLY ACTION IN TANA RIVER BASIN, KENYA

Abstract. Kenya is mostly affected by floods during the March-April-May (MAM) and October-November-December (OND) rainfall. This often occurs along river basins such as the Tana river basin, leading to disruption of people’s livelihoods, loss of lives, infrastructure destruction and interruption of economic activities. This study used openly available data on flood exposure, vulnerability, lack of coping capacity, flood impacts and observed satellite rainfall to analyse and predict forecast-based impacts in Tana river. Earth observation satellites including LANDSAT, sentinel 1 and 2 were acquired based on credible flood event dates to validate flood exposure and flood events. The community risk assessment (CRA) approach was used to delineate communities at high risk of floods using combination of data on vulnerability, flood exposure and lack of coping capacity. Using an ordinary least squares (OLS) predictive model, observed satellite rainfall was used as a covariate in order to predict flood impacts on communities with high flood risk scores in Tana river. Weighted scores from the CRA dimensions were summed up with forecasted hazards from the OLS model in order to derive a flood impact-based forecast. The flood impact information is to be used in forecast-based action through early warning, early action protocols thereby reducing impacts of potential floods in communities living in high flood risk areas based on the flood risk map.

CONSTRUCTING THE FLOOD EVACUATION ZONES BASED ON USER-CENTRIC TIME-DISTANCE REPRESENTATION

Abstract. In the current scenario, where there is no quantitative criteria for the location, size, etc. of the shelter, an empirical study was conducted on the location distribution of the shelter considering accessibility. In this study, a safety zone that can be immediately evacuated using a pedestrian-level network is set up for each shelter. For the case area, a GIS network analysis service area analysis was used to divide the area to be evacuated to each shelter and to generate a base map in which the shelter that can reach the shelter as soon as possible can easily be identified. It is possible to provide a suitable area and evacuation route using pedestrian networks. In an urgent situation, it should be possible to get to the evacuation shelter at least as soon as possible, to avoid the high risk of flooding. Therefore, the service area that considers the flooding maps to be effective for evacuation.

Climatic and social factors behind the Spanish Mediterranean flood event chronologies from documentary sources (14th–20th centuries)

Abstract The Spanish Mediterranean river basin provides a good background for studying floods from documentary and bibliographical sources within the specialty of historical climatology. This study region's long history of human occupation and climatic conditions together determine a high risk of flooding. As a result, there exists an enormous amount of documentary heritage containing flood information. However, the heterogeneity of documentary sources and different approaches to classifying floods through historical documents can generate some biases and uncertainties about the quantity and quality of the available data. For this reason, this paper proposes a methodology for reconstructing historical floods based on cross-referencing documentary sources. This approach, together with additional archival work, has allowed us to increase the number of flood series for the Spanish Mediterranean coast by 17% and has generated a surprising increase of 233% in the number of flood cases detected. The data obtained have allowed us to analyze the variability of floods and their relationship with climatic and social factors from the fourteenth century to the present. Different climatic oscillations related to the Little Ice Age are detected between the 14th and 19th centuries. Additionally, we detected a strong influence of the defense infrastructures and urban growth, which explain the recent flood trends. However, the difficulty in analyzing the influence of social factors on long-term flood behavior invites us to reflect on the need for further work for emphasizing these issues.

A Multi-Criteria Decision Support System in the Analysis of Flood Risk and Vulnerability Mapping in Suleja, Niger State, Nigeria

Abstract. This study aims at assessing flood risk factors and mapping areas vulnerable to flood in Suleja of Niger State, Nigeria, using Geo-spatial techniques. The method follows a multi-parametric approach and integrates some of the flood causative factors as: rainfall distribution, elevation and slope, drainage network and density, landuse/ land-cover and soil type. The Spatial Multi-Criteria Analysis (MCA) was used to rank and display potential locations, while the Analytical Hierarchy Process (AHP) method was employed using pair-wise comparison to compute the priority weights of each factor. The various layers were integrated in weighted overlay tool in ArcGIS to generate the final vulnerability map (high, moderate and low). The normalized criterion weights were obtained for each factor, and the results shows that, rainfall (34) and slope (31) have the highest influence on flood in the study area. The Consistency Ratio (CR) with an acceptable level of 0.05 was obtained which further validated the strength of the judgement. The factor weights from the AHP were incorporated to produce a Geo-hazard map and it showed that areas that are high vulnerable to flood in Suleja constitute about 37%, while moderate and low vulnerable areas constitute about 45% and 18% respectively. Elements at high risk of flood are those found at the extreme northeast, where elevation is very low, southwest where rainfall distribution is high and on low lying areas along the depressions. Therefore using the Geo-hazard map as a guide, local councils and other stakeholders can act to prepare for potential floods.

Flood risk assessment of metro systems in a subsiding environment using the interval FAHP-FCA approach

Metro systems are vulnerable to flooding during rainstorms and this situation worsens when a subsiding environment prevails. This study adopts the interval fuzzy analytic hierarchy process (FAHP) incorporated with fuzzy clustering analysis (FCA) to assess the flood risk of metro systems in subsiding environments, considering both the regional subsidence of the ground and the longitudinal settlement along metro lines as assessment factors. Shanghai metro system is analysed as an example by using the proposed method (the FAHP–FCA approach) together with the geographical information system (GIS). The assessment results show that more than 30% of metro lines in Shanghai are at a high risk of flooding, and the high-risk regions of metro lines are located in urban centres. The ratio of high-risk regions identified by the FAHP–FCA approach exceeds that obtained using the existing FAHP approach, which indicates that the FCA-FAHP approach can capture high-risk metro systems in Shanghai. Moreover, the comparison also shows that subsiding environments exacerbate the flood risk of metro systems. It is proposed that, to mitigate the risk of flooding, subsidence environments should be considered in more detail.

Application of Geographic Information Systems for Flood Risk Analysis: A Case Study from Accra Metropolitan Area

Abstract The main objective of the study was to identify high flood risk zones in AMA. The study also used questionnaires to assess local knowledge on what accounts for the high flood risk in their community. Spatial analysis techniques were used to model flood risk based on the following contributory factors; land cover, soil, drainage density, topography and proximity to rivers. The results show that high flood risk areas covered 46.3km2(20%), moderate risk area, 72.9km2(31.6%), low risk area 41.5km2(18%) and very low risk areas, about 6.7km2(2.9%). The high flood risk zones were low-lying areas below 50 meters above sea level and closely associated with poor drainage systems. People perceived not just low-lying areas as a paramount reason accounting for flooding but also very bad waste disposal habit of the public. These offsets the efforts of waste management companies to keep drains free of refuse.

Waiting after the storm: the effect of flooding on time on the housing market in coastal Virginia

ABSTRACTFlooding is the most common natural disaster experienced by many households and rising sea levels have made recurrent flooding events common in many coastal cities. This study uses a difference-in-differences model to estimate how the residential real estate market responds to significant flooding events. The analysis examines time-on-market for 137,348 residential property sales between 2007 and 2016 in southeast Virginia. This timeframe includes a Nor’easter, referred to as Nor’Ida, and Hurricane Irene. Results differentiate between high-risk (100-year flood plain) and low-risk (500-year flood plain) areas, and show that homes in the high-risk flood zones remain on the market 5–7 days longer. Our results suggest that the housing market cools down at a localized level after a severe weather event.

The Development and Application of the Urban Flood Risk Assessment Model for Reflecting upon Urban Planning Elements

As a city develops and expands, it is likely confronted with a variety of environmental problems. Although the impact of climate change on people has continuously increased in the past, great numbers of natural disasters in urban areas have become varied in terms of form. Among these urban disasters, urban flooding is the most frequent type, and this study focuses on urban flooding. In cities, the population and major facilities are concentrated, and to examine flooding issues in these urban areas, different levels of flooding risk are classified on 100 m × 100 m geographic grids to maximize the spatial efficiency during the flooding events and to minimize the following flooding damage. In this analysis, vulnerability and exposure tests are adopted to analyze urban flooding risks. The first method is based on land-use planning, and the building-to-land ratio. Using fuzzy approaches, the tests focus on risks. However, the latter method using the HEC-Ras model examines factors such as topology and precipitation volume. By mapping the classification of land-use and flooding, the risk of urban flooding is evaluated by grade-scales: green, yellow, orange, and red zones. There are two key findings and theoretical contributions of this study. First, the areas with a high flood risk are mainly restricted to central commercial areas where the main urban functions are concentrated. Additionally, the development density and urbanization are relatively high in these areas, in addition to the old center of urban areas. In the case of Changwon City, Euichang-gu and Seongsan-gu have increased the flood risk because of the high property value of commercial areas and high building density in these regions. Thus, land-use planning of these districts should be designed to reflect upon the different levels of flood risks, in addition to the preparation of anti-disaster facilities to mitigate flood damages in high flood risk areas. Urban flood risk analysis for individual land use districts would facilitate urban planners and managers to prioritize the areas with a high flood risk and to prepare responding preventive measures for more efficient flood management.

Evaluating urban growth and its implication on flood hazard and vulnerability in Srinagar city, Kashmir Valley, using geoinformatics

The present study investigates the urban growth in the Srinagar city of Kashmir Valley during 1972–2014 and the effect of 2014 Kashmir flood on the urban environment. Srinagar is the capital city in Kashmir Valley which has been affected by the devastating flood in 2014. The built-up growth for the past 42 years was 1565% with concomitant population growth of 224% in the Srinagar city. The built-up development was more pronounced in the central part of the city and along the river Jhelum during 1972–1989 which later on spread largely in the southernmost part of Srinagar city during the period of 1996–2014. High-Resolution Satellite (HRS) data-based observations indicated that 2014 flood inundation occupied 108 sq. km area within the Srinagar municipal limits. The increase of built-up inundation was monitored from 1972 to 2014, which reveals that the built-up inundation was 3.7 sq. km and increased to 39.2 sq. km. The spatial analysis revealed that nine wards located in the topographically low regions and in the proximity to Jhelum river were completely (100%) inundated during the flood. The past built-up inundation spatial analysis with reference to 2014 flood inundation indicated decrease in the percentage built-up area inundation (72.4% in 1972 to 46% in 2014) which reveals that the new built-up growth in the Srinagar city mostly occurred in the relatively safer zones. It is also observed that very high flood hazard and vulnerability zones were located in the western, southern, and central parts of the city in only 10 wards which rendered these wards with very high flood risk. The study demonstrated that geoinformatics-based spatial analysis of flood inundation can be effectively used for flood risk and related strategic planning.

Adoption of Individual Flood Damage Mitigation Measures in New York City: An Extension of Protection Motivation Theory.

This study offers insights into factors of influence on the implementation of flood damage mitigation measures by more than 1,000 homeowners who live in flood‐prone areas in New York City. Our theoretical basis for explaining flood preparedness decisions is protection motivation theory, which we extend using a variety of other variables that can have an important influence on individual decision making under risk, such as risk attitudes, time preferences, social norms, trust, and local flood risk management policies. Our results in relation to our main hypothesis are as follows. Individuals who live in high flood risk zones take more flood‐proofing measures in their home than individuals in low‐risk zones, which suggests the former group has a high threat appraisal. With regard to coping appraisal variables, we find that a high response efficacy and a high self‐efficacy play an important role in taking flood damage mitigation measures, while perceived response cost does not. In addition, a variety of behavioral characteristics influence individual decisions to flood‐proof homes, such as risk attitudes, time preferences, and private values of being well prepared for flooding. Investments in elevating one's home are mainly influenced by building code regulations and are negatively related with expectations of receiving federal disaster relief. We discuss a variety of policy recommendations to improve individual flood preparedness decisions, including incentives for risk reduction through flood insurance, and communication campaigns focused on coping appraisals and informing people about flood risk they face over long time horizons.

Flood risk zone mapping using rational model in a highly weathered Nitisols of Abakaliki Local Government Area, South-eastern Nigeria

ABSTRACT The lack of spatially explicit flood hazard mapping has hampered the development of appropriate flood interventions at community levels in Nigeria. This paper reports on a work conducted to develop a local government level flood hazard map to delineation flood vulnerable areas. Flood vulnerability mapping in this work was addressed from a perspective of administrative unit as the unit of investigation. The study is anchored on the Modeling Flow based on Relational Rule for flood assessment using ArcGIS in combination with modified rational model. The output of the modified rational model was integrated into the Geographic Information Systems environment by the arithmetic overlay operation methods. The results show that the delineated areas/sub-catchments however experienced the same rainfall intensity of 414.2 mm/h but the flood extents in the areas are different. For instance, the very high flood risk zone covers about 22.8% of the study area while the low risk zone covers about 44.3% and the possible areas likely to experience seasonal floods with a given rainfall input are mostly below 40 m elevation. The results of this study will be helpful to prioritize development efforts at grassroot in the study location and to formulate flood adaptation strategies.

The Belt and Road: Geographical pattern and regional risks

Building the Belt and Road is initiatives of China to promote win-win international cooperation in the new era, aiming at green, health, intellect and peace and the joint development with people of the countries along the route. Systematic analysis on environmental characteristics, evolutionary tendency and future risks are certainly the scientific fundamentals of sustainable development for the Belt and Road construction. Applied remote sensing monitoring, statistical analysis, this paper investigates the regional characteristics of climate, topography, soil, hydrology, vegetation cover and terrestrial ecosystems production, as well as socio-economic conditions. Based on the regional characteristics, the Belt and Road is divided into 9 sub-regions: Central and Eastern Europe sub-region with cold and humid climate, Mongolia and Russia sub-region with cold and arid climate, Central and West Asia arid sub-region, Southeast Asia sub-region with warm and humid climate, Pakistan arid sub-region, Bangladesh-India-Myanmar sub-region with warm and humid climate, Eastern China monsoon sub-region, Northwest China arid sub-region and Tibetan Plateau sub-region. Combining modeling simulation with scenario projections, natural disaster assessment methodology is used to assess the risk of extreme events including heat waves, droughts and floods in the coming 30 years (2021–2050). Results show that, on the basis of the regional framework, the western Eurasia would be a warming trend; both sides of Qinghai-Tibet Plateau in high temperature and heat waves risk; Central and Eastern Europe sub-region with cold and humid climate in high drought risk; Bangladesh-India-Myanmar sub-region with warm and humid climate as well as Eastern China in high risk of flooding.

Assessment of coastal vulnerability in Chabahar Bay due to climate change scenarios

Summary A substantial body of research has shown that two key factors of global sea level rise are thermal expansion and melting of land-based ice, glaciers and ice sheets. Moreover, climate change may result in changes to wind speeds and directions, consequently resulting in contributions to variations in wind-wave components, wave heights and directions. In this research, climate change scenarios were used to assess the coastal vulnerability to the Chabahar port area due to global sea level rise, significant wave height changes and tidal regime effects. These three items were calculated separately using numerical models and the impacts of possible climate change scenarios were applied to estimate possible changes to these items by 2100. Significant wave heights for 25, 50 and 100-year return periods were evaluated. Based on statistical analysis, the maximum significant wave heights for the A2 and A1B scenarios were estimated at approximately 13.7 and 7.6, respectively. Since the main aim of this research was to assess the coastal zones at higher flood risk, therefore the mean global sea level rise, extreme values of significant wave heights and tidal heights were investigated. The height of sea during sea storms and for the most extreme case was calculated as 17.3 m and 11.2 m for A2 and the A1B scenarios, respectively. According to output maps of inundation areas, large coastal zones in the Chabahar port area are at risk due to the sea storms and possible climate change.

Quantification of the Effect of Bridge Pier Encasement on Headwater Elevation Using HEC-RAS

The deterioration of bridge substructure is a serious concern across the United States. The pier encasement is one of the most common practices for repairing and strengthening the bridge substructure. It is a rehabilitation process of existing pile piers during the repair or replacement of the bridge superstructure, which involves enclosing part of an existing pile pier with a polyethylene or PVC pipe large enough to provide at least three inches of concrete cover over the existing pier when filled. However, this process of enclosing pile piers might elevate water level due to increase in pier width, which could be hazardous in high-risk flood zones. Furthermore, it may create an adverse impact on the stability of the bridge due to scouring around the pier foundation. In order to gain knowledge on the backwater effect due to pile encasement, Hydraulic Engineering Center-River Analysis System (HEC-RAS) was used in this research to perform hydraulic simulations near the bridge sites. These simulations were carried out for various channel configurations and pier sizes with a wide range of flows, which resulted into 224 HEC-RAS models in order to investigate the effects of pile pier encasement on the headwater elevation. This study demonstrated that the water elevation measured in the upstream of the bridge showed no-rise condition, especially for wider channel sections with flatter slopes. However, the water elevation at the immediate upstream of the bridge was slightly higher, and the increasing pattern was only noticeable for a smaller channel width (20 ft), and specifically, for increased flow rate. As the area of flow was decreased resulting in increased water surface elevation due to encasement, a generic power equation in the form of Y = aXb was suggested for various channel slopes for the increased water surface elevation (Y) for each percentage decrease in channel area (X).

Capitalization of Flood Insurance and Risk Perceptions in Housing Prices: An Empirical Agent‐Based Model Approach

Federally regulated or insured lenders in the United States are mandated to require flood insurance on properties that are located in areas at high risk of flooding. Despite the existence of this mandatory flood insurance requirement, take‐up rates for flood insurance have been low, and the federal government's exposure to uninsured property losses from flooding remains substantial. Meanwhile, the value of capital at risk varies significantly with flood events and changing risk perceptions, which necessitates mechanisms that stabilize these dynamics. In this article we discuss how a scenario of complete insurance uptake, under various risk attitudes, affects the value of properties in the 100‐year and 500‐year flood zones. Our results indicate that an increase in flood insurance uptake may provide such a mechanism by lowering the value of capital at risk in the flood zone consistently, independent of homeowners' risk attitudes. We apply an empirical adaptive agent‐based model to examine the capitalization of insurance costs, risk premiums, and their interaction in housing prices. Our approach combines widely‐used empirical hedonic analysis with the computational economic framework. We highlight the usefulness of our method in capturing the marginal implicit price of homeowners' preferences that may change over time and separately assess the effect of various factors and policies on property values, illustrating the agent‐based modeling as a valuable complement to traditional hedonic analysis.

Risk assessment and sensitivity analysis of flash floods in ungauged basins using coupled hydrologic and hydrodynamic models

Flash floods are among the most devastating natural hazards but the analyses of flash floods are hindered by the lack of hydro-meteorological data. In particular, data issues are critical in ungauged basins. This paper presents an investigation of flash flood modeling using coupled hydrological and hydrodynamic models. Specifically, the TOPography-based hydrological MODEL (TOPMODEL) is employed to obtain the flood hydrograph and the coupled 1D-2D hydrodynamic model MIKEFLOOD is used to simulate floodplain inundation. The methods are tested in the Pajiang River, a mountainous basin in South China. The results show that the TOPMODEL effectively simulates the flood hydrograph and the Nash–Sutcliffe coefficients of the flow rate are larger than 0.80 for both calibration and validation. Also, MIKEFLOOD effectively simulates the flood inundation extent and flooding depth and the BIAS for simulated water level is −0.004 m. Further, using socioeconomic and historical flood disaster datasets, areas with high flash flood risk are identified. A flash flood risk assessment shows a clear trend of change in the flood hazard and the spatial heterogeneity of the flood vulnerability is significant. A sensitivity analysis of the flood vulnerability to the socioeconomic indicators indicates that cultivated land is the most sensitive indicators, and the population and the construction areas have similar influences. Overall, the coupled hydrological and hydrodynamic models prove effective and can be used in practical applications for flash flood risk mapping.