Flood vulnerability, risk and social disadvantage: current and future patterns in the UK

Present day and future social vulnerability, flood risk and disadvantage across the UK are explored using the UK Future Flood Explorer. In doing so, new indices of neighbourhood flood vulnerability and social flood risk are introduced and used to provide a quantitative comparison of the flood risks faced by more and less socially vulnerable neighbourhoods. The results show the concentrated nature of geographic flood disadvantage. For example, ten local authorities account for fifty percent of the most socially vulnerable people that live in flood prone areas. The results also highlight the systematic nature of flood disadvantage. For example, flood risks are higher in socially vulnerable communities than elsewhere; this is shown to be particularly the case in coastal areas, economically struggling cities and dispersed rural communities. Results from a re-analysis of the Environment Agency’s Long-Term Investment Scenarios (for England) suggests a long-term economic case for improving the protection afforded to the most socially vulnerable communities; a finding that reinforces the need to develop a better understanding of flood risk in socially vulnerable communities if flood risk management efforts are to deliver fair outcomes. In response to these findings the paper advocates an approach to flood risk management that emphasizes Rawlsian principles of preferentially targeting risk reduction for the most socially vulnerable and avoids a process of prioritisation based upon strict utilitarian or purely egalitarian principles

Using airborne laser altimetry to improve river flood extents delineated from SAR data

Flood extent maps derived from SAR images are a useful source of data for validating hydraulic models of river flood flow. The accuracy of such maps is reduced by a number of factors, including changes in returns from the water surface caused by different meteorological conditions and the presence of emergent vegetation. The paper describes how improved accuracy can be achieved by modifying an existing flood extent delineation algorithm to use airborne laser altimetry (LiDAR) as well as SAR data. The LiDAR data provide an additional constraint that waterline (land-water boundary) heights should vary smoothly along the flooded reach. The method was tested on a SAR image of a flood for which contemporaneous aerial photography existed, together with LiDAR data of the un-flooded reach. Waterline heights of the SAR flood extent conditioned on both SAR and LiDAR data matched the corresponding heights from the aerial photo waterline significantly more closely than those from the SAR flood extent conditioned only on SAR data

Utility of different data types for calibrating flood inundation models within a GLUE framework

International audienceTo translate a point hydrograph forecast into products for use by environmental agencies and civil protection authorities, a hydraulic model is necessary. Typical one- and two-dimensional hydraulic models are able to predict dynamically varying inundation extent, water depth and velocity for river and floodplain reaches up to 100 km in length. However, because of uncertainties over appropriate surface friction parameters, calibration of hydraulic models against observed data is a necessity. The value of different types of data is explored in constraining the predictions of a simple two-dimensional hydraulic model, LISFLOOD-FP. For the January 1995 flooding on the River Meuse, The Netherlands, a flow observation data set has been assembled for the 35-km reach between Borgharen and Maaseik, consisting of Synthetic Aperture Radar and air photo images of inundation extent, downstream stage and discharge hydrographs, two stage hydrographs internal to the model domain and 84 point observations of maximum free surface elevation. The data set thus contains examples of all the types of data that potentially can be used to calibrate flood inundation models. 500 realisations of the model have been conducted with different friction parameterisations and the performance of each realisation has been evaluated against each observed data set. Implementation of the Generalised Likelihood Uncertainty Estimation (GLUE) methodology is then used to determine the value of each data set in constraining the model predictions as well as the reduction in parameter uncertainty resulting from the updating of generalised likelihoods based on multiple data sources

Flood vulnerability, risk and social disadvantage: current and future patterns in the UK

Present day and future social vulnerability, flood risk and disadvantage across the UK are explored using the UK Future Flood Explorer. In doing so, new indices of neighbourhood flood vulnerability and social flood risk are introduced and used to provide a quantitative comparison of the flood risks faced by more and less socially vulnerable neighbourhoods. The results show the concentrated nature of geographic flood disadvantage. For example, ten local authorities account for fifty percent of the most socially vulnerable people that live in flood prone areas. The results also highlight the systematic nature of flood disadvantage. For example, flood risks are higher in socially vulnerable communities than elsewhere; this is shown to be particularly the case in coastal areas, economically struggling cities and dispersed rural communities. Results from a re-analysis of the Environment Agency’s Long-Term Investment Scenarios (for England) suggests a long-term economic case for improving the protection afforded to the most socially vulnerable communities; a finding that reinforces the need to develop a better understanding of flood risk in socially vulnerable communities if flood risk management efforts are to deliver fair outcomes. In response to these findings the paper advocates an approach to flood risk management that emphasizes Rawlsian principles of preferentially targeting risk reduction for the most socially vulnerable and avoids a process of prioritisation based upon strict utilitarian or purely egalitarian principles