Possible impacts of a changing climate on intense Ligurian Sea rainfall events

The region near the Ligurian Sea in northwestern Italy occasionally experiences extreme rainfall events that can lead to catastrophic flooding. These events are often caused by back-building mesoscale convective systems whose occurrence peaks during the autumn. Rapid warming of the Mediterranean Sea in recent decades has raised concerns that the warmer water may change the frequency or intensity of these rainfall events. To gain insight into possible impacts of the warming climate, surface wind and precipitation output from 12-km horizontal grid spacing EXPRESS-Hydro simulations of past and future climate are used to examine trends in the frequency of strong convergence and heavy rainfall events during both the past and the future climate. Strong convergence events are not found to increase in frequency in the future climate, but the rainfall associated with these events does increase. The area that experiences rainfall above a specified threshold along with the duration over which such conditions are experienced increases, especially during the autumn when increases are statistically significant. Peak 3-hourly rainfall at a grid point does not increase in the future climate but total rain volume associated with these events does, reflecting the larger areal coverage and duration of the events.