Atmospheric circulation anomalies and impact mechanisms behind the extreme heat and drought event over the Yangtze River Basin in 2022

In the midsummer of 2022, the Yangtze River Basin experienced a historically rare extreme compound event of high temperature and drought. Investigating its causes and impact mechanisms is of great significance for the scientific understanding of extreme climate events. This study utilizes daily maximum temperature observations collected at 720 national meteorological stations across the Yangtze River Basin and the meteorological drought composite index (MCI) as well as the NCEP/NCAR reanalysis data to systematically analyze atmospheric circulation anomalies and influencing mechanisms of sea surface temperature (SST) as an external forcing. Results indicate that during the summer of 2022, the Western Pacific subtropical high (WPSH) and South Asian high (SAH) exhibited unprecedented intensification and dominated the Yangtze River Basin, with their intensities reaching historical extremes. An abnormally northward shifted 200 hPa subtropical westerly jet (SWJ) formed a warm ridge, effectively blocking the convergence of cold and warm air masses. The Yangtze River Basin was controlled by an anomalous anticyclonic circulation, which led to significant water vapor divergence. The re-intensification of the La Niña event and the record-breaking strengthening of the negative phase of the tropical Indian Ocean dipole (TIOD) jointly enhanced the descending branches of both the Walker and Hadley circulations, which, aided by the SWJ, further intensified the deep high-pressure system over the Yangtze River Basin, ultimately resulting in the prolonged extreme high temperature and drought event. It is worth noting that the interdecadal warming of the Indian Ocean warm pool (IOWP) and the Western Pacific warm pool (WPWP) has led to increasingly significant impacts on the WPSH and SAH. Their influences have exceeded that of SST anomalies in the equatorial central-eastern Pacific, making them key predictors for sub-seasonal to seasonal forecasting.