Here we present results from decade-long convection-resolving regional climate simulations at Alpine and European scales (Ban et al. 2014, 2015; Leutwyler et al. 2016a, 2016b) with a spatial resolution of 2.2 km using the COSMO model. The European-scale simulations employ a computational domain with 1536x1536x60 grid points. Such simulations have become feasible with a model version that runs entirely on Graphics Processing Units (Fuhrer et al. 2014, Leutwyler et al. 2016a, 2016b). Comparison against simulations with parameterized convection demonstrate that hourly events are much better captured at convection-resolving resolution -- in terms of diurnal cycle, precipitation frequency, and extreme events. Scenario simulations with an RCP8.5 emissions scenario suggest that for the summer season, when mean precipitation is projected to decrease significantly over Southern Europe and the Alps, the intensity of extreme events increases consistently with the Clausius-Clapeyron scaling, i.e. heavy events asymptotically increase with <7%/K, i.e. much slower than the super-adiabatic scaling suggests.
Analysis reveals that some of these differences are related to the different use of precipitation percentiles (Schar et al. 2016). Lenderink and van Meijgaard (2008) used wet-hour percentiles that are conditional upon the occurrence of precipitation. We demonstrate that our results are consistent with their analyses. In particular, observations and simulations exhibit a wet-hour super-adiabatic scaling. Yet, when considering the results in terms of all-hour percentiles, which is more relevant in term of impacts, results demonstrate that the currently observed wet-hour scaling cannot be extrapolated into the future, as changes in precipitation frequency are intimately linked to changes in wet-hour occurrence.