Simplified graphical tools for assessing flood-risk change over large flood-prone areas

We propose and investigate the reliability of simplified graphical tools, which we term Hypsometric Vulnerability Curves, HVCs, for assessing flood vulnerability and risk over large geographical areas and for defining sustainable flood-risk mitigation strategies. These curves rely on the use of inundation scenarios simulated by means of quasi-two-dimensional (quasi-2-D) hydrodynamic models that reproduce the hydraulic behaviour of the floodable area outside the main embankment system of the study river reach. We present an application of HVCs constructed on the basis of land use and census data collected during the last 50 years for assessing the recent dynamics of the flood vulnerability and risk over a large floodable area along a 350 km stretch of the River Po (Northern Italy). We also compared the proposed simplified approach with a traditional approach based on simulations performed with the fully-2-D hydrodynamic model TELEMAC-2-D, a widely employed and well-known 2-D finite-element scheme. By means of this comparison, we characterize the accuracy of the proposed simplified approach (i. e. quasi-2-D model and HVCs) for flood-risk assessment over large geographical areas and different historical land-use scenarios.