Shifting of summertime weather extremes in Western Europe during 2012–2020

Over the past decades, droughts and heatwaves frequently appeared in Western Europe (45°–65°N, 10°W–20°E) during boreal summer, causing huge impacts on human society and ecosystems. Although these extremes are projected to increase in both frequency and intensity under a warming climate, our knowledge of their interdecadal variations and causes is relatively limited. Here we show that the droughts and heatwaves in Western Europe have shifted in their trends in the last decade: for 1979–2012, wind speed and precipitation have both strengthened in Western Europe; for 2012–2020, however, Western Europe have experienced declined wind speed, decreased precipitation, and higher air temperature, leading to more frequent droughts and heatwaves there. Recent changes in the WE climate and extremes are related to the variations of the North Atlantic westerly jet stream. In 1979–2012 (2012–2020), the westerly jet stream shifted equatorward (poleward), which enhanced (reduced) transportation of water vapor fluxes from the North Atlantic Ocean to the European land areas, resulting in wetter (drier) surface in Western Europe. Further analysis suggests that phase changes in the Pacific Decadal Oscillation could have played a key role in regulating the position of the jet stream, providing important implications for decadal predictions of the Western Europe summertime climate and weather extremes.We acknowledged supports from the National Natural Science Foundation of China (42088101), the Swedish Research Council (VR: 2017-03780 and 2019-03954), the Swedish FORMAS (2018-02858), the Ramon Y Cajal Fellowship (RYC-2017-22830), the Spanish Ministry of Science, Innovation and Universities (RTI2018-095749-A-I00), China Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies (2020B1212060025), the Second Tibetan Plateau Scientific Expedition and Research Program (2019QZKK0606), the Swedish MERGE and BECC, and the China Jiangsu Collaborative Innovation Center for Climate Change. The computational resources were provided by the Swedish National Infrastructure for Computing at the National Supercomputer Centre in Sweden