Observational evidence for soil-moisture impact on hot extremes in southeastern Europe

Climate change is expected to affect not only the means of climatic variables, but also their variabilities(1,2) and extremes such as heat waves(2-6). In particular, modelling studies have postulated a possible impact of soil-moisture deficit and drought on hot extremes(7-11). Such effects could be responsible for impending changes in the occurrence of heat waves in Europe(7). Here we analyse observational indices based on measurements at 275 meteorological stations in central and southeastern Europe, and on publicly available gridded observations(12). We find a relationship between soil-moisture deficit, as expressed by the standardized precipitation index(13), and summer hot extremes in southeastern Europe. This relationship is stronger for the high end of the distribution of temperature extremes. We compare our results with simulations of current climate models and find that the models correctly represent the soil-moisture impacts on temperature extremes in southeastern Europe, but overestimate them in central Europe. Given the memory associated with soil moisture storage, our findings may help with climate-change-adaptation measures, such as early-warning and prediction tools for extreme heat waves.