Projected future changes of very extreme precipitation events over central European river catchments from ensemble climate simulations

Extreme precipitation events can cause flooding in central European river catchments. Climate simulations show that extreme precipitation, especially towards longer return periods, will intensify in a warmer climate for most parts of Europe. In order to study the mechanisms leading to the intensification of particularly extreme events, we investigate 10-year daily precipitation events over five major central European river catchments in Community Earth System Model Large Ensemble simulations. A statistical evaluation and comparison of large-scale circulation patterns associated with the events with operational ensemble weather prediction data from the ECMWF indicate a realistic representation of the 10-year extreme events in the climate model. Differences in these circulation patterns are analysed between the historical climate of 1990-2000 and a warmer climate at the end of the century (2091-2100). While most events occur in the core summer months (June-August) in the historical climate, there is a broadening of the seasonal distribution with extreme events from May to October in the warmer climate. Precipitation rates increase locally by 5-7%/K, similar to the Clausius-Clapeyron rate, related to significant increases in lower-tropospheric humidity. Averaged over the entire catchments, precipitation still increases, but with lower intensification rates varying between 1.2 and 3.8%/K for the individual catchments. This is due to a combination of thermodynamic and dynamic factors, in particular the shift towards the cold season, associated with smaller temperature increases during the events than expected from the overall warming, and a weakening of vertical motion over parts of the catchments. In future research, the robustness of these findings should be investigated through comparison with other climate simulations.