Projected changes in synoptic circulations over Europe and their implications for summer precipitation: A CMIP6 perspective

Abstract: Projected changes in summer precipitation deficits partly depend on alterations in synoptic circulations. Here, the automated Jenkinson-Collison (JC) classification is used to assess the ability of twenty-one Global Climate Models (GCMs) to capture the frequency of recurring circulation types (CTs) and their implications for European daily precipitation intensities in summer (JJA). The ability of the GCMs to reproduce the observed present-day climate features is first evaluated. Most GCMs capture the observed links between mean directional flow characteristics of the CTs, and the occurrence of dry days and related dry months. The most robust relationships are found for anticyclonic and easterly CTs which are generally associated with higher than average occurrences of dry conditions. Future changes in summer frequencies of the CTs are estimated in the high-emissions SSP5-8.5 scenario for the sake of a high signal-to-noise ratio. Our results reveal consistent changes, mainly in the zonal CTs. A robust decrease in frequency of the westerlies and increase in the frequency of easterly CTs favour more continental, dry and warm air masses over Central Europe. These dynamical changes are shown to enhance the projected summer drying over central and southern Europe.