High-resolution precipitation over the southern Balkans

The main climatic characteristics of precipitation in the southern Balkans were examined by applying S-Mode and T-Mode factor analysis (FA) to APHRODITE 0.25 degrees x 0.25 degrees grid point precipitation data for the period 1951-2007. First, S-Mode FA was applied to the seasonal precipitation values and revealed the main modes of interannual variation of precipitation for each season. These modes were found to be connected to specific atmospheric circulation centers of action. Statistically significant negative trends were found for: (1) winter and spring precipitation over northwestern Greece and southern Albania and (2) spring and autumn precipitation over the southern Aegean Sea. Next, T-Mode FA was applied to the 57 yr mean precipitation of 5 d intervals (n = 73) in a year and resulted in 3 main modes of spatial distribution of precipitation: (1) the cold period mode (late November to late March) with maxima in northwestern Greece and the western Asia Minor coasts, (2) the warm period mode (late April to late August), presenting a maximum over the northern continental areas, and (3) the autumn mode (early September to late October) with a maximum found over the northern Ionian Sea. The intra-annual variations of the prevalence degree of these modes are connected to the seasonality of the thermal characteristics of the surface and the overlying atmospheric layers and the main circulation systems affecting the region.