Rainfall statistics changes in Sicily

Changes in rainfall characteristics are one of the most relevant signs of current climate alterations. Many stud- ies have demonstrated an increase in rainfall intensity and a reduction of frequency in several areas of the world, in- cluding Mediterranean areas. Rainfall characteristics may be crucial for vegetation patterns formation and evolution in Mediterranean ecosystems, with important implications, for example, in vegetation water stress or coexistence and com- petition dynamics. At the same time, characteristics of ex- treme rainfall events are fundamental for the estimation of flood peaks and quantiles that can be used in many hydro- logical applications, such as design of the most common hydraulic structures, or planning and management of flood- prone areas. In the past, Sicily has been screened for several signals of possible climate change. Annual, seasonal and monthly rainfall data in the entire Sicilian region have been analyzed, showing a global reduction of total annual rainfall. More- over, annual maximum rainfall series for different durations have been rarely analyzed in order to detect the presence of trends. Results indicated that for short durations, historical series generally exhibit increasing trends, while for longer durations the trends are mainly negative. Starting from these premises, the aim of this study is to in- vestigate and quantify changes in rainfall statistics in Sicily, during the second half of the last century. Time series of about 60 stations over the region have been processed and screened by using the nonparametric Mann-Kendall test. In particular, extreme events have been analyzed using an- nual maximum rainfall series at 1, 3, 6, 12 and 24 h duration, while daily rainfall properties have been analyzed in terms of frequency and intensity, also characterizing seasonal rainfall features. Results of extreme events analysis confirmed an in- creasing trend for rainfall of short durations, especially for 1 h rainfall duration. Conversely, precipitation events of long durations have exhibited a decreased trend. Increase in short- duration precipitation has been observed especially in sta- tions located along the coastline; however, no clear and well- defined spatial pattern has been outlined by the results. Out- comes of analysis for daily rainfall properties have showed that heavy-torrential precipitation events tend to be more fre- quent at regional scale, while light rainfall events exhibited a negative trend at some sites. Values of total annual precip- itation events confirmed a significant negative trend, mainly due to the reduction during the winter season.