Changes in future precipitation characteristics over the Alpine region in a multi-model convection-permitting ensemble: the role of shifting intensities

Changes in precipitation at local to regional scales in a warmer world remain highly uncertain. This is especially true of both moderate and high extremes (e.g. > 90%-iles and > 99.9%-iles, respectively). While a relationship between increasing model resolution and increasing precipitation (both means and extremes) appears to be present for both GCMs and RCMs there are conflicting results when convection-permitting scales are reached. These differences can be region as well as model dependent. A project under the auspices of the World Climate Research Program’s (WCRP) Coordinated Regional Downscaling Experiments Flagship Pilot Studies program (CORDEX-FPS) was established to investigate these, and other issues. This initiative aims to build first-of-their-kind ensemble climate experiments using convection permitting models to investigate present and future convective processes and related extremes over Europe and the Mediterranean. In this presentation we offer a first look at the scenario simulations (Historical 2000-2009 and RCP8.5 2090-99 timeslices) and an analysis of precipitation changes and their drivers over various sub-regions of a large domain, which cover the Alps, parts of central Europe and the Mediterranean and Adriatic coasts (0-17E x 40-50N). This study employs an innovative precipitation separation algorithm specifically designed for use with km-scale models. The algorithm separates convective, stratiform and orographic precipitation, which allows for a more nuanced understanding of projected change. The method is based on physical processes such as vorticity and vertical velocity. This new approach focuses on the physical processes leading to precipitation of a certain types rather than use the circular reasoning of employing the result to determine the cause. As a result we are able to see that despite overall drying in some seasons increasing intensity of convective precipitation contributes toward the shift to more intense extremes. We conclude with a discussion of the changes to the underlying physical processes driving convective and other types of precipitation at highly localized scales.