1Nansen-Zhu International Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
2Climate Change Research Center, Chinese Academy of Sciences, Beijing 100029, China
3Uni Climate, Uni Research, Bergen, Norway
4Nansen Environmental and Remote Sensing Center, Bergen, Norway
5Geophysical Institute, University of Bergen, Bergen, Norway
6Bjerknes Centre for Climate Research, Bergen, Norway
*now at: Nansen-Zhu International Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
Abstract. Observation shows that eastern China has experienced an interdecadal shift in the summer precipitation during the second half of the 20th century. The summer precipitation increased in the middle and lower reaches of the Yangtze River Valley, whereas it decreased in northern China. Here we use a coupled ocean–atmosphere general circulation model and multi-ensemble simulations to show that the interdecadal shift is mainly caused by the combined effect of increasing global greenhouse gases and regional aerosol emissions over China. The rapidly increasing greenhouse gases induce tropical warming and a westward shift of the western Pacific subtropical high, leading to more precipitation in Yangtze River Valley. At the same time the aerosol cooling effect over land contributes to a reduced summer land–sea thermal contrast and therefore to a weakened East Asian summer monsoon and to drought in northern China. Consequently, an anomalous precipitation pattern starts to emerge in eastern China in late 1970s. Our results highlight the important role of anthropogenic forcing agents in shaping the weakened East Asian summer monsoon and associated anomalous precipitation in eastern China.