Rainfall regime and seasonality changes in semi-arid Mediterranean areas: Evidence from three regions of southern Italy (1922–2022).

Global warming is significantly altering precipitation patterns in the Mediterranean Basin, a region already susceptible to water scarcity and extreme weather events. Changes in precipitation can exacerbate both drought conditions and soil degradation caused by increasingly erosive rainfall. Where wet season patterns mismatch peak irrigation demands, shifts in rainfall seasonality may pose a serious threat to agricultural sustainability. This study analyses century-long (1922–2022) trends in three regions of Southern Italy representative of Mediterranean semi-arid areas (i.e., Campania, Sardinia, and Sicily), using a wide spectrum of rainfall regime indicators. A novel methodological framework is applied to an extensive database of daily rainfall time series from over 700 rain gauges, using both point-based (at gauge level) and spatially distributed analyses. This approach ensures the robust detection and localization of trends in precipitation characteristics, with a particular focus on rainfall seasonality. Results indicate consistent temporal variations across the three regions for most indicators, including reduction in mean annual precipitation, frequency and length of dry and wet spells. Crucially, the study area exhibits reduced rainfall seasonality compared to previous historical periods, with earlier onset and longer duration of the wet season. These shifts have profound implications for water resource management, agricultural planning, and ecosystem resilience across the Mediterranean. Furthermore, spatial autocorrelation analysis highlights that some trends are highly localized, identifying priority areas for the implementation of targeted climate change adaptation strategies.