Evidence for Increasing Rainfall Extremes Remains Elusive at Large Spatial Scales: The Case of Italy

The widespread perception of an increase in the severity of extreme rainstorms has not found yet clear confirmation in the scientific literature, often showing vastly different results. Especially for short-duration extremes, spatial heterogeneities can affect the outcomes of large-scale trend analyses, providing misleading results dependent on the adopted spatial domain. Based on the availability of a renewed and comprehensive database, the present work assesses the presence of regional trends in the magnitude and frequency of annual rainfall maxima for subdaily durations in Italy. Versions of the Mann-Kendall test and a record-breaking analysis, which considers the spatial correlation, have been adopted for the scope. Significant trends do not appear at the whole-country scale, but distinct patterns of change emerge in smaller domains having homogeneous geographical characteristics. Results of the study underline the importance of a multiscale approach to regional trend analysis and the need of more advanced explanations of localized trends.