EWRA 2015 - Proceedings

Several studies investigating long term changes in rainfall pattern over the Mediterranean area, have shown that the average number of rainy days is decreased during the last decades, whereas precipitation intensity is increased at the same time, as more and more heavy rainfall have occurred in shorter periods. In particular, an intensification of extreme rainfall events have recently characterized several areas of peninsular and insular Italy. In the present study temporal changes in 1-, 3-, 6-, 12- and 24-hour annual maxima rainfall series from more than 200 sites between 1928 and 2009 in Sicily region (Italy) are examined. For a more accurate analysis of extreme events, annual maxima series are first treated according to a standard regional frequency analysis to produce growth curves for homogeneous regions. First a cluster analysis using at-site characteristics is used to determine homogeneous rainfall regions. Then, L-moments and the modified Anderson-Darling rank test statistic are applied to verify the homogeneity of the clusters. Several commonly applied probability distributions, namely the Lognormal (LN3), Generalized Extreme Value (GEV), Generalized Pareto (GPA), Generalized Logistic (GLO), Pearson type III (PE3) and Weibulll (W3) are investigated to derive regional growth curves. Hence, potential changes in L-moment ratios and regional growth curve shapes during the observation period are analysed using a 11-year moving window and by splitting the records into separate decades. In addition, a jackknife technique is used to assess uncertainty in the fitted growth curves and to identify significant trends in quantile estimates. Results reveal that, despite L-moment ratios show a general decreasing long term trend and that growth curves corresponding to the last decade (2000-2009) are usually less steep than the ones of the previous periods, rainfall quantile estimates have increased during the 2000s due to a large increase in regional average median, mainly in Eastern and Western Sicily.