Analysis of Alpine precipitation extremes using generalized extreme value theory in convection-resolving climate simulations

We present an analysis of extreme precipitation events in convection-resolving climate simulations. The simulations are performed with the COSMO-CLM model at 2.2 km resolution across an extended Alpine region and its larger-scale surrounding. Generalized extreme value theory (GEV) is applied to address projections of 5-day, daily and hourly extreme precipitation events in all seasons. Validation using ERA-Interim driven simulations reveals significant improvements with the 2.2 km resolution. In comparison to its driving 12 km model, high resolution improves the simulation of precipitation on most investigated timescales and seasons. The climate change signal is analyzed in 10-year long control and scenario simulations (1991-2000 and 2081-2090) driven by a CMIP5 coupled climate model (MPI-ESM-LR) under an RCP8.5 greenhouse gas scenario. Analysis shows negligible differences between the two resolutions for winter precipitation on all time scales, while in the other seasons the 2.2 km model shows smaller changes in extreme hourly precipitation, and yields narrower uncertainty estimates. Changes in extreme summer precipitation qualitatively scale with the Clausius-Clapeyron rate, i.e., 6-7% per degree warming, and are consistent with previous percentile based analysis. In winter, changes exceed the Clausius-Clapeyron rate. Some interpretations of this result are provided.