A classification of high-risk atmospheric circulation patterns for Italian precipitation extremes

Precipitation extremes are a significant natural hazard that has caused considerable destruction in Italy over the past decade. However, our understanding of the effects of climate change on these extremes remains incomplete, with unclear trends in the intensity and frequency of precipitation extremes. As a first step to address this issue, here we develop a comprehensive classification of the Weather Types (WTs) associated with 1985-2019 Extreme Precipitation Events (EPEs) in the 156 operational Warning Areas (WAs) used by the Italian Department of Civil Protection by applying  Self-Organizing Maps to sea level pressure and 500 hPa geopotential height. We identify six different WTs influencing EPEs in Italy associated with different large-scale dynamical drivers:  Atlantic cyclone over France/northern Tyrrhenian Sea (WT1), Mediterranean cyclone over Central Italy (WT2), Western Mediterranean cyclone associated with upper level trough over Iberia (WT3), Westerly zonal flow (WT4), Western Mediterranean cyclone associated with upper level trough over North Italy and ridge over Southern Italy (WT5), and Mediterranean cyclone over Southern Italy (WT6). The relevance of these WTs for different WAs is evaluated through composites of moisture transport, the probability of EPEs to be associated with each WT and their seasonality. Trend analysis for the annual frequency of these circulation patterns shows no significant trends, with the except of WT3 which has experienced a significant increase in autumn. These results add to the existing knowledge of drivers of extreme precipitation events in Italy, providing an understanding of underlying large-scale atmospheric circulation and a tool to investigate the role of anthropogenic climate change in  climate model simulations.