Real-time Assessment of Flash Flood Impacts at pan-European scale: The ReAFFINE method

Abstract The development of early warning systems (EWSs) is a key element for the effective mitigation of flash flood impacts. Emergency managers and other end-users increasingly recognise the benefit of tools that automatically translate the forecasted flash flood hazard (e.g. expressed in terms of peak discharge or return period) into the expected socio-economic impacts (e.g. the affected population). While previous studies aimed at forecasting flash flood impacts at local or regional scales, this paper presents a simple approach for estimating in real time the flash flood impacts across Europe. The proposed method – named ReAFFINE – is designed to be integrated into an EWS for end-users operating over large spatial domains (e.g. across regions or countries). ReAFFINE uses the pan-European flash flood hazard estimates from the ERICHA system to retrieve the potentially flooded areas from the national flood maps (generated in the framework of the EU Floods Directive). By combining the potentially flooded areas with socio-economic exposure information, ReAFFINE estimates in real time the exposed population and critical infrastructures. For two catastrophic flash flood events affecting Europe in recent years, ReAFFINE has demonstrated the capability to identify impacts over large spatial scales. Also at sub-regional level, the method has mostly been able to locate the areas and municipalities where the most important impacts occurred. The results also show that the performance is sensitive to the quality of the rainfall estimates that drive the hazard estimation, and to the comprehensiveness of the employed flood maps.