From CMIP6 to eddy-rich models: does very-high resolution improve the representation of Mediterranean heavy precipitation events?

Abstract. The Mediterranean region is a recognized climate-change hotspot where heavy precipitation events are frequently associated with cut-off lows (COLs). However, traditional climate models show limited skill in representing both the climatology of these systems and their relationship with extreme rainfall. Here, we assess the impact of horizontal resolution on the simulation of Mediterranean COLs and associated precipitation using four very-high-resolution simulations from the EERIE project and eighteen standard-resolution CMIP6 models, with ERA5 reanalysis as reference.

Results show that all models underestimate COL frequency over the Mediterranean, although this bias is substantially reduced in the eddy-rich EERIE simulations, particularly over the western Mediterranean. Reanalysis indicates that COLs contribute to 20–40 % of total precipitation across much of the region, but their importance increases markedly for upper-tail events, accounting for more than 60 % of precipitation exceeding the 99th percentile over large areas. In contrast, CMIP6 models largely fail to reproduce this enhanced COL contribution to extremes. Several EERIE simulations, however, capture these observed relationships more realistically and produce substantially larger precipitation maxima associated with COLs.

Future projections suggest a decrease in COL occurrence over the western and central Mediterranean, but contrasting responses in associated extreme precipitation emerge between EERIE and CMIP6 simulations. These results highlight the importance of very-high-resolution climate simulations for representing Mediterranean precipitation extremes and reveal persistent uncertainties in their future evolution.