The climate characteristic of extreme precipitations for short term Intervals in the watershed of Lake Maggiore

The Alpine and Mediterranean areas are undergoing a profound change in the typology and distribution of rainfall. In particular, there has been an increase in consecutive non-rainy days, and an escalation of extreme rainy events. The climatic characteristic of extreme precipitations over short-term intervals is an object of study in the watershed of Lake Maggiore, the second largest freshwater basin in Italy (located in the north-west of the country) and an important resource for tourism, fishing and commercial flower-growing. The historical extreme rainfall series with high-resolution from 5 minutes to 45 minutes and above - 1, 2, 3, 6, 12 and 24h - collected at different gauges located at representative sites in the watershed of Lake Maggiore, have been computed to perform regional frequency analysis of annual maxima precipitation based on the L-moments approach, and to produce growth curves for different return-period rainfall events. The different rainfall-generating mechanisms in the watershed of Lake Maggiore, such as elevation, meant that no single parent distribution could be found for the entire study area. This paper describes an investigation designed to give a complete view of the temporal change and evolution of annual maxima precipitation, focusing particularly on both heavy and extreme events recorded at time intervals ranging from a few minutes to 24h, and also to create and develop an extreme storm precipitation database, starting from historical sub-daily precipitation series distributed over the territory. There have been two-part changes in extreme rainfall events occurring in the last 24 years, from 1987 to 2009. Little change is observed in 720 min and 24-hour precipitations, but the change seen in 5, 10, 15, 20, 30, 45, 60, 120, 180 and 360 min events is significant. In fact, during the 2000s, growth curves have flattened and annual maxima have decreased.