Event-based analysis of extreme precipitation trends in Italy using hourly convection-permitting reanalyses

Abstract. The latest generation of high-resolution and convection-permitting reanalyses, capable of representing atmospheric processes at small spatial scales (≤4 km), is crucial for studying the temporal and spatial evolution of phenomena such as convective storms and orographic precipitation. Given the availability of long (>35 years) and continuous convection-permitting reanalysis datasets over Italy, this study investigates the occurrence and characteristics of hourly extreme precipitation events (EPEs) and quantifies their potential increase over time in this region. Using the MERIDA HRES reanalysis (1986–2022), precipitation events are extracted from hourly fields as spatially coherent structures, yielding approximately 160,000 events per year. Each event is characterized by intensity and shape indicators. The resulting HOPE-X (HOurly Precipitation Events and Xtremes) dataset enables a detailed climatological analysis of event frequency, intensity, and spatial scale across seasons. The most extreme component of those events (EPEs), defined based on the mean of local annual maxima in hourly precipitation (RX1hour), show a pronounced increase in occurrence. Specifically, significant upward trends are present during summer in several Alpine and Prealpine regions, as well as in parts of Calabria. In autumn, significant signals emerge in the southern Apennines and in coastal and maritime areas, including the eastern Ligurian coast, eastern Sardinia, the southern Adriatic Sea, and the Ionian Sea. These spatial and seasonal patterns align with regions where convective processes predominantly drive intense, localised precipitation, potentially amplified by climate change. While these findings should be considered in light of known limitations of reanalysis products, such as spatial mismatches with observations and temporal inhomogeneities, multiple independent observational studies support the increase in EPEs during summer and autumn in specific areas. Moreover, the methodology presented here is broadly applicable in any region with access to long-term convection-permitting reanalysis data. In summary, this study offers a contribution to the ongoing discussion on precipitation extremes in Italy and provides guidance for leveraging reanalysis data to enhance infrastructure resilience to short-lived, intense precipitation events.