Recent hot and dry summers in Germany in comparison to climate projections

This study investigates whether the recent extremely hot and dry summers (2003, 2015, 2018 and 2019) in Germany will be normal summers under future climate change conditions from climate projections. Abnormally persistent high-pressure systems during these recent German summers maintained clear skies and dry conditions on the ground, resulting in record-breaking heat and drought conditions which had major socio-economic impacts, e.g. reduced crop yields or impacts on human health and increased mortality. Heat and drought indices are calculated from the German Meteorological Service's (DWD) climate model reference-ensembles for periods 2031-2060 and 2071-2100 under greenhouse gas emission scenarios RCP 2.6 (11 ensemble members) and RCP 8.5 (21 ensemble members). These results are compared with the same indicators calculated from three observational datasets (station data and gridded datasets: HYRAS and DWD Climate Monitoring Grids). The order of recent extreme summers in Germany from hottest and driest is: 2018, 2003, 2019, 2015. The climate projections show increasing summer heat conditions for Germany throughout this century, especially for the RCP 8.5 scenario, but no clear future summer precipitation anomaly trend. These recent extreme summers would be considered extremely hot summers for RCP 2.6 in 2031-2060, 2071-2100 and the RCP 8.5 2031-2060 scenarios, but would be considered normal or even below normal hot summers under the RCP 8.5 scenario in 2071-2100. Due to the combination of extreme heat and strong precipitation deficits, the climatic water balance and derived meteorological drought indicator values of these summers often exceeds the considered likely ranges projected for all future summer scenarios and are only matched by the most anomalous hot and dry summers in the model ensembles, even for the high-emission RCP 8.5 scenario in 2071-2100.