Meteorological to hydrological drought propagation using the large ensemble of regional climate model simulations for Europe (LAERTES-EU). A case study for the Rhine River Catchment

The last twenty years have shown the most extreme drought events in Europe on record. In the Rhine River basin, these droughts have severely impacted the shipping and industry sectors due to low water levels limiting the transport of goods. Drought prediction, therefore, is crucial but difficult to achieve due to the complexities of the propagation from meteorological to hydrological droughts. In this study, we analyzed the relation between several meteorological drought indices and the occurrence of hydrological droughts. We found that the Standardized Precipitation Evapotranspiration Index (SPEI) shows the highest correlation. SPEI was then used to single out extreme meteorological droughts from the LAERTES-EU data set, which contains about 12.500 years of meteorological variables simulated under current climate conditions by several setups of the regional COSMO-CLM model. These most extreme meteorological droughts were then propagated through the hydrological model WRF-Hydro to produce streamflow at the Rhine, which was then evaluated in terms of hydrological drought severity by comparison with observed hydrological droughts. Overall, this approach reveals insights into the magnitude of extremely rare hydrological droughts, and their predictability from the corresponding meteorological drought indices.