Understanding past changes in precipitation extremes could help us
predict their dynamics under future conditions. 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 distribution and occurrence frequency of
storms. We examine the relevant case of the eastern Italian Alps, where
significant trends in annual maximum precipitation over the past decades
were observed. The model is able to reproduce observed trends at all
durations between 15 minutes and 24 hours, and allows to quantify trends
in extreme return levels. Despite the significant increase in storms
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 these are caused by an increased proportion of summer
convective storms.