Unveiling Changes in the Seasonality of Extreme Precipitation Shows an Anticipation of Short-Duration Extremes

Climate change is significantly modifying the characteristics of extreme precipitation events, with relevant implications for society and water-related risks. While most studies focus on changes in the magnitude or frequency of this hazard, this work investigates shifts in the seasonality of extreme precipitation across the Sicily Island over a period spanning almost 100 years. We use circular statistics to characterize the seasonality of annual maximum precipitation at canonical durations. By applying two different circular-linear regression tests (i.e., a Generalized Linear Model developed for circular outcomes within the Bayesian framework and a circular-adapted version of the Theil-Sen slope estimator), we also analyze changes in the extreme events timing over time. Our findings reveal a general anticipation in the timing of extreme events, particularly for short durations, reaching up to similar to 20 days over the study period (1928-2018) and aligning with previous studies reporting increasing severity of short-lived extremes in the region. By integrating circular statistics with spatial clustering methods, we also identify seasonal clusters that reflect the spatial coherence of extreme precipitation timing. In this case as well, especially at shorter durations, a particularly distinct cluster of stations emerges in the northeastern part of the island, an area known to be highly affected by intense convective events and prone to flash floods. This study has a twofold significance. First, it challenges the conventional paradigm in the analysis of seasonality of extreme precipitation by introducing a novel, robust methodology that fully respects the circular nature of the data and can be extended to other geographical contexts or to different variables. Second, it highlights how changes in the timing of extremes are more pronounced for short-duration events, an aspect that could have substantial consequences for flash flooding, urban drainage systems, and agricultural planning, particularly in regions already vulnerable to climate change impacts.