The climatological contribution of Mediterranean cyclones to precipitation and ocean evaporation

The Mediterranean region is highly sensitive to climate change, largely due to the variable response of its hydrological cycle. Mediterranean cyclones are the major weather system governing the variability of precipitation (P) and ocean evaporation (E). Mediterranean cyclones themselves are a heterogeneous group of systems in terms of their development mechanisms and surface impact, ranging from winter baroclinic lows to transition-season convective systems and spring heat lows over land, governed by different upper-level forcing and interaction with the lower troposphere and near surface. It is, however, unclear how P and E respond to different types of cyclones, and if any links emerge between observed trends in Mediterranean cyclones, P and E.

Here we integrate P and E under the influence of differently-driven cyclones by combining climatological ERA5 datasets (1980-2020) of P and E, composite cyclone tracks and a recent potential-vorticity based cyclone classification. Our results confirm the prime importance of Mediterranean cyclones for yearly means of P and E. We find alternating dominance of different cyclone types in different regions and seasons, with the strongest precipitation and ocean evaporation attributed to the winter cyclones, and the least contribution to both quantities from spring and summer systems. Interestingly, climatological P-E budget varies by cyclone type, and display variable, and at time, opposing observed trends. The trends are tightly linked to Mediterranean cyclones and are largely a result of changing cyclone frequency and/or P and E totals per cyclone. Overall, if observed trends continue, we expect P to decrease and E to increase due to decreasing P and increasing E per some winter cyclones and increasing frequencies of non-precipitating heat lows.