Helmi, Saidi (2013) Extreme storm precipitations events in a changing climate: how to define and analyze (case of the Lake Maggiore watershed). Doctoral Thesis.
In recent years we are assisting in Alpine region to a profound change in rainfall typology and distribution. We can observe an increase in consecutive non-rainy days, and an escalation of extreme rainy events. In this study, the historical extreme rainfall series with high-resolution (5min-24h) collected at different gauges located 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. I used rainfall statistic methodology to check whether the automatic TBR Gauges was working effectively during extreme events. In four selected stations in our study we noticed an underestimation of extreme events. I carried out an automatic conversion of rain data from paper records into digital numerical format regarding four sites. Using this method we obtained long time series of precipitation with high temporal resolution (5min-12hour). Finally I examined the long-term historical change in frequency and amplitude of extreme precipitation events collected and digitized in four stations. We adopted two indices of extremes and Peaks-Over-Threshold approach. The application of Mann-Kendall test showed significant positive trend of the extreme frequency index and spring maximum precipitation for Bra and Lombriasco. The temporal change of growth curve proved that extreme short rainfall events have risen during the last 20 years.
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