Extreme Rainfall in a changing climate: regional analysis and hydrological implications in Tuscany

A comprehensive analysis of the extreme rainfalls in Tuscany, Italy, is carried out with the aim of understanding and quantifying the uncertainties connected with the estimation of the design storms, which is very important for a sound basin management at urban or larger scales. The historical extreme rainfall series of durations 1, 3, 6, 12 and 24 h collected at 81 rain gauges located at representative sites in Tuscany are computed to detect a possible trend by means of two tests: the Pearson linear correlation coefficient and the Mann-Kendall test. The generalized extreme value distribution is employed to compute design storms with a 30 years return period; hence a preliminary map of the most hazardous areas is built up. The design storms are then computed for several consecutive 20 year moving time windows (1 year step) to evaluate intrinsic (climatological) uncertainties in the series. A regionalization of the difference between the design storms calculated for different periods is performed. The hydrological consequences of this kind of climate variability are demonstrated to have a major impact on the design of hydraulic works in a basin.