Spatial and temporal variability of precipitation over the Mediterranean Basin based on 32-year satellite Global Precipitation Climatology Project data. Part-II: Inter-annual variability and trends

Monthly mean satellite data from the Global Precipitation Climatology Project (GPCPv2) are used to examine the year-by-year variability of precipitation over the Mediterranean Basin and its changes over the period 1979-2010. The results show that the mean annual precipitation averaged over the study area has slightly increased from 1979 to 2010 by 1.28mm or by 0.2% (trend not statistically significant at the 95% confidence level). Nevertheless, examining the trends at a local scale, spatial and temporal patterns are revealed, with opposite trends in adjacent areas and increasing precipitation in summer and autumn against almost unchanged or decreasing precipitation in winter and spring, respectively. Inter-decadal changes of precipitation are detected, with precipitation decreasing in the 1980s, then increasing through the late 1990s and finally declining in the 2000s before levelling off since 2007. These changes are significantly anti-correlated (R=-0.57, up to -0.66 in winter) with the North Atlantic Oscillation (NAO) index, thus confirming the critical role of this large-scale teleconnection for the regional precipitation over the basin.