Southern Germany's 100-year flash flood discharge expected to increase by 30 % under an RCP8.5 climate

Abstract. The frequency and intensity of convective heavy rainfall events are generally assumed to increase in a warming climate. So far, however, it remained difficult to assess the corresponding changes in flash floods. This difficulty resulted from the mismatch between the coarse spatial resolution of global and regional circulation models, which do not explicitly resolve convective processes, and the small spatial extent of flash-flood-prone headwater catchments. Recently, though, the results of several convection-permitting climate models (CPMs) became available for parts of Germany. Our study presents the first attempt to utilize these high-resolution data (1 h, 3 km) for an assessment of flash-flood changes in southern Germany. Based on an ensemble of 6 CPM models, we simulated the runoff for the periods 1971–2000 (historical) and 2071–2100 under the RCP8.5 scenario for the German part of the Danube basin. We then compared the 100-year return levels of rainfall and discharge maxima between these two periods. The results indicate an increase of 100-yr flood return levels for 94 % of the Danube subcatchments with a median increase of 30 % across all subcatchments under the RCP8.5 scenario.