Trend analysis of hourly rainfall in the Mediterranean: a case study of the Basilicata Region, Southern Italy (2001–2024)

This study examines recent trends in sub-daily rainfall extremes across the Basilicata region of southern Italy – a Mediterranean climate-change hot spot – using high-resolution hourly data from 32 well-distributed stations, covering years 2001–2024. A comprehensive set of fixed-threshold and percentile-based indices was applied to describe the occurrence, intensity and spatial variability of short-duration rainfall. Trend analyses were conducted using the Mann-Kendall test and Theil-Sen slope estimator, with adjustments for autocorrelation (TFPW) and multiple testing (Benjamini Hochberg False Discovery Rate, BH-FDR). Preliminary results indicate widespread upward tendencies in both frequency and intensity of sub-daily rainfall extremes, particularly for events exceeding the 95th and 99th percentiles, with over 80% of stations showing positive trends, most evident in summer and autumn. After BH-FDR correction, no individual station exhibited statistically significant changes; however, the complementary Field Significance Test (FST) revealed spatially coherent regional signals, with summer intensification and winter decline. Comparisons among physiographic zones (Kruskal- Wallis test) showed stronger trends in mountainous and high-hilly sectors, confirming elevation as a key control on short-duration rainfall variability. Overall, moderate extremes (95th percentile) have intensified, while the most severe events (99th − 99.9th percentiles) remain stationary. These results align with broader Mediterranean evidence suggesting a seasonal redistribution of precipitation toward the warm period. The integrated statistical framework adopted here effectively distinguishes genuine climatic signals from natural variability, offering robust guidance for hydrological risk assessment and climate adaptation planning in Mediterranean environments.