Warming Asian Drylands Inducing the Delayed Retreat of East Asian Summer Monsoon and Intensifying Autumn Precipitation in Northern China

In the early 21st century, there was an increase in precipitation during the retreat period of the East Asian summer monsoon (EASM). This study aims to explore the precipitation changes and their possible causes in the context of climate change. The findings indicate that the increased precipitation primarily occurred in the Yellow-Huai River valley during the early autumn. This corresponds to a delayed retreat of the EASM with a northward shift of 0.9 degrees N after 2002. Notably, this anomalous changes in the EASM are associated with the significant warming in two Asian dryland regions. The warming of the central Asian dryland strengthens the midlatitude high-pressure belt and the anomaly anticyclone over northeast Asia, which restrains the development of wave troughs and westerly cold air activity. Similarly, the warming China-Mongolia dryland enhances the anomaly anticyclone over northeast Asia through the dry soil moisture feedback and reduced latitudinal temperature gradient. These two Asian drylands thereby hold the northward shift of the westerly jet stream and the northwest extension of the Japan Sea high and the western Pacific subtropical high. These changes result in maintaining the northward EASM circulation and driving the northwest water vapor flux from the northwest Pacific, leading to moisture convergence in northern China. The China-Mongolia dryland warming also increases the land-sea thermal contrast, which induces a dipole pattern over East Asia and drives the northward water vapor flux from the South Sea. As a result, the rapidly warming drylands restrict westerly activity and EASM retreat, ultimately leading to increased precipitation.