Increasing probability of record-breaking precipitation: A case-study in the Eastern Italian Alps

Study region: Rotian river catchment, Adige river basin, Eastern Italian Alps. Study focus: Time-dependent precipitation frequency analyses are often hampered by the availability of relatively short data records, which result in large uncertainty in the estimation of extremes. Non-asymptotic statistical methods, based on ordinary events rather than extreme events only, represent a potential solution to the problem of data scarcity and are finding application in literature under the assumption of stationarity. This study adopts a time-dependent model for the statistical analysis of sub-hourly to multi-day precipitation extremes based on the Simplified Metastatistical Extreme Value (SMEV) approach. The aim is twofold: (i) evaluate the time-dependence in extreme precipitation probability over the past decades and (ii) estimate the temporal variations in the annual exceedance probabilities of the record-breaking Vaia storm by focusing on a catchment that was severely impacted by the event. New Hydrological Insights for the Region: Precipitation extremes in the study region increase over time, particularly for short durations. The largest increase in the design rainfall is observed for sub-hourly and hourly durations, indicating that enhanced convective activity can be a major factor driving the observed changes in the intensity and frequency of precipitation extremes. We find that the probability of observing events like Vaia increased significantly over the past decades, leading to the need for updating local adaptation measures.