Monthly and daily precipitation trends in the Mediterranean (1950-2000)

The aim of the paper lies in the identification of possible significant linear trends at monthly, seasonal and annual timescales in the Mediterranean during the second half of the 20th century. Monthly and daily records of 63 stations have been used to elaborate several precipitation indices: sum of daily precipitation (SDP) for rainfall > 0.1 mm, > 10 mm and > 9(th) percentile, of number of rainy days (RD) > 0.1 mm and > 10 mm and of mean daily precipitation (MDP) > 0.1 mm and > 10 mm. For each index the stations have been gathered together by Rotated Principal Component Analyses to determine 8 sub-areas which can be considered as identical for all the timescales at the spatial scale of the research. Trends have been estimated from the scores of each eigenvector retained in all RPCAs. They are mainly non existant or non significant decreasing, even if a few monthly trends appear to be significantly diminishing, primarily during winter months, March in the Atlantic region, October in the Mediterranean Spain, December in the Lions and Genoa Gulfs, January, winter and the year in Greece, winter and the year in Italy and winter in the Near East and increasing in April in the two gulfs. Correlation coefficients between SDP > 0.1 mm and other indices have been computed: the significant trends seem mainly related to RD > 10mm, which represents a high percentage of the total rainfall amount. Greece is remarkable: SDP > 0.1 mm and > 10 mm decrease significantly during January, winter, the rainy season and the entire year whereas SDP > 95(th) percentile increases significantly, in accordance with the climatic change scenarios for the end of this century as does the decreasing of the total monthly and seasonal rainfall.