Monthly rainfall changes in Central and Western Mediterranean basins, at the end of the 20th and beginning of the 21th centuries

Changes in the statistical distribution of rainfall amounts have been studied in four Mediterranean regions:the French and Spanish Mediterranean coasts, Sardinia Island, and the Calabrian region, in Italy. The largest precipitationseries (from 70 to 150 years) in these zones have been collected and studied at yearly and monthly time scales by meansof different parametric and nonparametric techniques. Nonparametric procedures have focussed on continuous time serieschanges, while possible changes at the end of the 20th century have been studied developing a parametric method. Amongthe results obtained, the 1984/1985 to 1994/1995 and 1994/1995 to 2004/2005 decades have been revealed as some ofthe driest ones since data are available in central and western Mediterranean. Despite that, such a finding is not alwaysaccompanied with a trend in the entire rainfall series. On the one hand, the low precipitation amounts detected in CentralMediterranean are caused in its major contribution by a diminution of the winter rainfall. On the other hand, a diminutionof the spring and winter rainfall is the cause of the driest records since data are available in Western Mediterranean.Possible relations between the dry records and seasonal SLP-based indexes have been studied. The seasonal configurationsof the North Atlantic Oscillation (NAO) have been calculated and their time series have provided a good perspective onthe evolution of the most contributive synoptic patterns to climate variability at the region. The high frequency of positiveseasonal phases of winter, spring and autumn NAO at the end of the 20th century and beginning of the 21st have been foundas possible dynamic mechanism causing the last decades dryness. Moreover, moving correlations suggest a strengthening inthe correlation between those seasonal NAOs and precipitation anomalies in Central and Western Mediterranean.