Mediterranean summer temperature and winter precipitation, large-scale dynamics, trends

In this contribution we summarize results on the large-scale influence of the atmospheric circulation at several tropospheric levels and Mediterranean SSTs on wet season precipitation and warm season temperature across the Mediterranean area covering the last few decades. Three large-scale predictor fields (300 hPa geopotential height, 700–1000 hPa thickness and SSTs) account for more than 50% of the total summer temperature variability over the Mediterranean area. The positive phase of the first most important canonical mode is associated with blocking conditions, subsidence and stability related to warm Mediterranean summers. The second CCA mode shows an east-west dipole of the Mediterranean summer air temperature connected by a combination of a trough as well as an extended ridge over the western and eastern parts of the Mediterranean, respectively. It is mainly the first mode which is responsible for the significant 0.4◦ C warming over the last 50 years of the twentieth century. In the context of the last 500 years it comes apparent that the hot summers of the decade 1994-2003 seem to be unprecedented. The hottest larger Mediterranean summer over the last half millennium was in 2003, in agreement with findings from the whole of Europe. It is found that around 30% of the total Mediterranean October to March precipitation variability can be accounted for by the combination of four large-scale geopotential height fields and sea level pressure. Results show that the North Atlantic Oscillation (NAO) seems to play an important role in interannual to centennial low frequency variability of wet season precipitation over the studied area. In the western and northern part, the correlation between precipitation and the NAO is negative, whereas for the southeastern part mostly positive correlations have been found. The analysis further reveals that since the mid-nineteenth century precipitation steadily increased with a maximum in the 1960s and decreased since then. The second half of the twentieth century shows a general downward trend of 2.2 mm/month/decade