Projections of heavy precipitation characteristics over the Greater Alpine Region using a kilometer-scale climate model ensemble

This study presents the detailed analysis of a novel and first-of-its-kind 10-year multi-model ensemble of kilometer-scale convection-permitting climate model (CPM) simulations over the Greater Alpine Region. The simulations were obtained by downscaling global climate model (GCM) projections using regional climate models (RCMs) and further downscaling to the kilometer scale using convection-permitting climate models (CPMs) . This study evaluates the CPMs and assesses their added value with respect to RCMs regarding basic and heavy precipitation characteristics. In addition, this study assesses projected changes for the end of the century. The analysis is performed for climatological seasons, for different temporal aggregations between 1 hour and 5 days, and for various precipitation indices.. ERA-Interim-driven and historical GCM-driven CPM simulations are compared against daily and hourly observational datasets, as well as their driving RCM counterparts to evaluate their performance and added value. Evaluation reveals that CPMs refine spatial patterns, reduce the overestimation of precipitation frequency and better capture intense precipitation characteristics, especially on the sub-daily scale and in summer. Climate change projections show an intensification of precipitation for all seasons and across all temporal aggregation levels. During summer, mean precipitation and precipitation frequency are projected to decrease, especially in the Mediterranean. In winter, an increase is projected across most parts of the Alps. CPMs and RCMs show agreement, with CPMs indicating slightly amplified signals and reduced model spread. The findings are consistent with previous studies using individual simulations, but provide one of the first multi-model assessment of projections in heavy precipitation over the Alps.