Widespread multi-year droughts in Italy: identification and causes of development

Multi-year droughts pose a significant threat to the security of water resources, putting stress on the resilience of hydrological, ecological, and socioeconomic systems. Motivated by the recent multi-year drought that affected Southwestern Europe and Italy from 2021 to 2023, here we utilize two indices - the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) - to quantify the temporal evolution of the percentage of Italian territory experiencing drought conditions in the period 1901-2023 and to identify Widespread Multi-Year Drought (WMYD) events, defined as multi-year droughts affecting at least 30% of Italy. Seven WMYD events are identified using two different different precipitation datasets: 1921-22, 1942-43, 1945-46, 2006-08, 2011-13, 2015-19 and 2021- 23. Correlation analysis between the time series of Italian drought areas and atmospheric circulation indicates that the onset and spread of droughts in Italy are related to specific phases of the winter North Atlantic Oscillation (NAO), the Scandinavian Pattern (SCAND), East Atlantic/Western Russia (EAWR) pattern and of the summer East Atlantic (EA) and East Atlantic/Western Russia (EAWR) patterns. Event-based analysis of these drought episodes reveals a variety of atmospheric patterns and combinations of the four teleconnection modes that contribute to persistently dry conditions in Italy during both winter and summer. This study offers new insights into the identification and understanding of Italian WMYD events and serves as a first step toward a better understanding of the impacts of anthropogenic climate change on them.