Future heat extremes and impacts in a convection-permitting climate ensemble over Germany

Heat extremes and associated impacts are considered the most pressing issue for German regional governments with respect to climate adaptation. We explore thepotential of a unique high-resolution, convection-permitting(2.8 m), multi-GCM (global climate model) ensemble with COSMO-CLM (Consortium for Small-scale Modeling Cli-mate Limited-area Modelling) regional simulations (1971-2100) over Germany regarding heat extremes and related im-pacts. We find a systematically reduced cold bias especially in summer in the convection-permitting simulations com-pared to the driving simulations with a grid size of 7 km and parametrized convection. The projected increase in temperature and its variance favors the development of longer and hotter heat waves, especially in late summer and early autumn. In a 2(degrees)C (3(degrees)C) warmer world, a 26 % (100 %) increase in the heat wave magnitude index is anticipated. Human heat stress (universal thermal climate index (UTCI)>32 degrees C) andregion-specific parameters tailored to climate adaptation revealed a dependency on the major landscapes, resulting insignificantly higher heat exposure in flat regions such as the Rhine Valley, accompanied by the strongest absolute in-crease. A nonlinear, exponential increase is anticipated for parameters characterizing strong heat stress (UTCI>32(degrees)C,tropical nights, very hot days). Providing region-specific and tailored climate information, we demonstrate the potential of convection-permitting simulations to facilitate improved impact studies and narrow the gap between climate modeling and stakeholder requirements for climate adaptation.