Uncertainty of future changes of very extreme precipitation events over central European river catchments from ensemble simulations of multiple global climate models

Historical extreme precipitation events over Central European river catchments often resulted in flooding events. Climate simulations show an increasing intensity of very extreme precipitation in a warmer climate for most parts of Europe. In order to analyse the atmospheric mechanisms leading to the intensification of very extreme precipitation events, we investigate 100-year daily precipitation events over Central European river catchments from large ensembles of multiple CMIP6 global climate models. Extreme events are identified in a historical (1970-2000) and a future (2070-2100, ssp370) period and uncertainties of projected changes are quantified through inter-model differences. Also, future changes are separated into dynamic and thermodynamic contributions with the precipitation scaling diagnostic by O’Gorman & Schneider (2009) and compared to synoptic composites in order to identify the main sources of uncertainty of projected changes and to understand the underlying mechanisms. Extreme precipitation events in the historical period mainly occur during the core summer season (June-August), while there is a slight broadening of the seasonality in the future period towards May and October. Averaged over all models, precipitation intensity in each catchment significantly increases by about 6-9%/K, similar to the Clausius-Clapeyron rate, but the increases vary regionally across models and catchments. This multi-model uncertainty is partly due to a varying representation of dynamical processes between most models, as indicated by the scaling diagnostic, while they mostly agree on a rather homogeneous precipitation increase due to thermodynamic mechanisms. Composites show that projected future changes in the synoptic situation during the extreme events are generally small. Nevertheless, significant changes both in dynamical parameters, such as an intensifying ridge over the North Atlantic, and thermodynamic variables, e.g. larger total column water vapour, enhance the precipitation rate in future events.