Enhanced summer convection explains observed trends in extreme subdaily precipitation in the Eastern Italian Alps

Understanding past changes in precipitation extremes could help us predict their future dynamics. We present a novel approach for analyzing trends in extremes and attributing them to changes in the local precipitation regime. The approach relies on the separation between intensity and occurrence of storms. We examine the relevant case of the Eastern Italian Alps, where significant trends in extreme precipitation were reported. The model is able to reproduce the observed trends at all durations between 15 min and 24 hr, and allows us to quantify trends in extreme return levels. Despite the significant increase in storm occurrence and typical intensity, the observed trends can be only explained considering changes in the tail heaviness of the intensity distribution, that is the proportion between heavy and mild events. Our results suggest that the observed changes are caused by an increased proportion of summer convective storms.