Which models for extreme flood events in Mediterranean catchments?

Abstract

Over the last years, most of the Mediterranean countries have been affected by catastrophic flood events generated by never observed before extreme rainfalls. Those events are frequently convective and stationary for several hours. The recorded intensities have frequently values exceeding 100 mm/hour and can last for several hours. Under those specific conditions as during the storm ALEX of October 2020, the runoff processes are particularly intense and can generate massive floods. Mitigation strategies should be developed and based on modeling that can support the understanding of the processes and the forecast the magnitude of the flood events and the associated impacts. The choice of the relevant hydrological modeling tools is a key element. The selected ones should be able to provide the relevant information, on time and with the relevant accuracy for the decision makers. The hydrological deterministic distributed models have reached a sufficient maturity to provide an accurate representation of the processes. The storm ALEX was generating more than 500 mm in less than 6 hours and producing a devastating flood within the Vésubie valley (France) in October 2020. The analysis of the event has demonstrated the difficulty to obtain consistent field observations and the limitations of many stochastic hydrological tools. The application of the AquaVar approach, combining several distributed deterministic models, has demonstrated its capacity to generate meaningful hydrographs and to quantify process with the catchment. The proposed solution is currently implemented within a real-time decision support system and can be used in real-time.