Flash flood forecasting, warning and risk management: the HYDRATE project

► We characterize flash flood events in various regions of Europe. ► We provide guidance to improve observations and monitoring of flash floods. ► Flash floods are associated to orography and are influenced by initial soil moisture conditions. ► Models for flash flood forecasting and flash flood hazard assessment are illustrated and discussed. ► We examine implications for flood risk policy and discuss recommendations received from end users. The management of flash flood hazards and risks is a critical component of public safety and quality of life. Flash-floods develop at space and time scales that conventional observation systems are not able to monitor for rainfall and river discharge. Consequently, the atmospheric and hydrological generating mechanisms of flash-floods are poorly understood, leading to highly uncertain forecasts of these events. The objective of the HYDRATE project has been to improve the scientific basis of flash flood forecasting by advancing and harmonising a European-wide innovative flash flood observation strategy and developing a coherent set of technologies and tools for effective early warning systems. To this end, the project included actions on the organization of the existing flash flood data patrimony across Europe. The final aim of HYDRATE was to enhance the capability of flash flood forecasting in ungauged basins by exploiting the extended availability of flash flood data and the improved process understanding. This paper provides a review of the work conducted in HYDRATE with a special emphasis on how this body of research can contribute to guide the policy-life cycle concerning flash flood risk management.