Trockenheit und Trockenperioden im südlichen Mitteleuropa: Zusammenhänge mit der atmosphärischen Zirkulation

Drought in southern Central Europe: Connections to the atmospheric Circulation: Based on gridded precipitation data with a resolution of 6 km regions of similar precipitation variability were derived for southern Central Europe. Between 1961 and 2017, precipitation in the summer half-year (April to September) decreased significantly north of the Alps, in the winter half-year (October to March) south of the Alps. Days without precipitation are occurring more frequently in both seasons throughout nearly the entire study area. To investigate correponding changes in atmospheric circulation, large-scale circulation types were derived using an optimized non-hierarchical cluster analysis. The combination of sea level pressure, relative humidity at the 700 hPa level, U and V wind components at the 700 hPa level, temperature at 2 m height and the regional precipitation time series proved to be especially suitable for generating drought-relevant atmospheric circulation types. Prominent examples are ridges from the Azores’ High with a cut-off cell above eastern Central Europe (summer half-year) and extended high pressure centered above southeastern Europe (winter half-year). Future changes were analyzed using different regional climate models (from Cordex and ReKliEs-De) for different greenhouse gas scenarios (RCP4.5 and RCP8.5) in two projection periods (2031-2060 and 2071-2100). Drought-relevant circulation types with higher temperatures will occur much more frequently and persistently in a warmer climate, while their type-internal high-pressure centers will expand in a northwesterly direction.