Extreme Mediterranean cyclones under future climate change

Abstract. The Mediterranean storm track is characterized by small but intense cyclones that can cause extreme weather events across the region. Thus the aim of this study is to investigate the impact of future climate change on extreme wind, precipitation and compounding cyclones. Using a regional climate model simulation, we show that the mean cyclone frequency is reduced by roughly a third in the Mediterranean by the end of the 21st century under the representative concentration pathway RCP8.5. For precipitation-type extreme cyclones (EXCs), future projections show increased precipitation during their most intense phase in the western Mediterranean (WMED), whereas precipitation from these cyclones remains similar in the eastern Mediterranean (EMED). Moreover, precipitation EXCs in the EMED are shifted southward, whereas the latitude of precipitation EXCs in the WMED remain unchanged in the future. The intensification of WMED precipitation EXCs in the future is partly explained by a significant increase in diabatically produced PV during their mature phase. Wind speed EXCs become more intense in both the WMED and EMED in the future under RCP8.5. The reason for this intensification is that wind speed EXCs in the future are located on the left exit of the jet streak, the latter also being intensified in the future. The future change of compounding precipitation and wind speed cyclones is similar to the individual precipitation and wind speed EXCs, with the exception that wind speed of compounding EXCs is reduced in the EMED. Thus, we find that despite a general reduction of cyclones in the Mediterranean, precipitation and wind speed EXCs intensify in the future in some areas, which implies strong socio-economic consequences for the Mediterranean.