A Classification of High‐Risk Atmospheric Circulation Patterns for Italian Precipitation Extremes

ABSTRACT 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. Part of this uncertainty results from internal variability in atmospheric circulation, which is key in triggering high‐impact precipitation events. To address this issue, here we develop a comprehensive classification of the Weather Types (WTs) associated with November 1984 to October 2024 Extreme Precipitation Events (EPEs) from CERRA in the 156 operational warning areas used by the Italian Department of Civil Protection, by applying Self‐Organising Maps to sea level pressure and 500 hPa geopotential height. We identify six different WTs associated with Italian EPEs, corresponding to 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), upper‐level cut‐off low (WT5), and Mediterranean cyclone centered over the Tyrrhenian Sea (WT6). The relevance of these WTs for different warning areas is evaluated through composites of moisture transport, the probability of EPEs given a specific WT and a seasonality analysis. The annual frequency of extreme precipitation events exhibits a statistically significant increasing trend (Mann‐Kendall, p < 0.05), corresponding to an average rise of more than two additional events per year per decade. The positive trend in precipitation extremes occurs for five out of the six WTs, with the largest increase occurring for WT4. 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 database of weather types to investigate the role of anthropogenic climate change in climate model simulations.