An assessment of actual evapotranspiration and soil water deficit in agricultural regions in Europe

Changes in agricultural droughts were investigated using simulations of soil water deficit (SWD) and actual evapotranspiration (ETA) from a distributed semi-empirical soil water balance model-swbEWA. At European scale, both SWD and ETA did not change significantly between 1951 and 2011. However, significant increases in SWD were found in southern Europe, except in western Turkey, whereas in northern Europe changes in SWD remain small. ETA increased significantly as a joint response to increased air temperature and precipitation in northern Europe. Using the Empirical Orthogonal Function (EOF) analysis and the Pearson correlation coefficients (R-Pearson), we showed that large-scale agricultural droughts are influenced by the recurrence of the North Atlantic Oscillation (NAO) and by the atmospheric blocking. Atmospheric blocking in different months throughout the year and extreme NAO index (mainly in winter months) contribute to the severity of agricultural droughts. During a negative phase of NAO, storms over the North Atlantic and Europe are less frequent and as a consequence dry weather in Europe is observed. Positive NAO influences agricultural drought in Europe by shifting storms tracks from the North Atlantic onto European continent to more northerly paths, which in turn decreases the amount of precipitation over central Europe. Large SWDs are mainly influenced by atmospheric blocking. Notably, winter blocking increases severity of agricultural droughts in southwestern Europe, while summer blocking influences agricultural droughts in southeastern Europe. Notwithstanding, the first three EOFs contribute to less than 40% of the total spatial variability of SWD. This shows that agricultural droughts are complex phenomena that can be only partly explained by extreme NAO or by intensive atmospheric blocking.