Comparative analysis of peak-summer heatwaves in the Yangtze-Huaihe River Basin of China in 2022 and 2013: Thermal effects of the Tibetan Plateau

In the peak-summer of 2022, the Yangtze-Huaihe River Basin (YHRB) in China experienced its most extreme heatwaves since 1961. Notably, a rare heatwave also occurred in the YHRB in 2013. However, the Tibetan Plateau (TP) exhibited different thermal conditions during those two years. Observational analysis indicates that the 2013 and 2022 heatwaves were closely related to the local anomalous high pressure. The synergistic effects of the East Asian subtropical jet (EASJ), South Asian high (SAH), western Pacific subtropical high (WPSH), and divergence of moisture, supported the formation and maintenance of the high pressure. Compared to 2013, under the synergistic control of these intensified circulation systems in 2022, which led a broader descending motion and stronger heatwaves prevailed over the YHRB. Also, the surface air temperature of TP reached its highest value in 2022, whereas it was not distinctly anomalous in 2013. Corresponding to the TP thermal anomaly, an abnormal high pressure appeared throughout the troposphere over the northern YHRB. The TP heating contributed to the northward strengthening of the SAH and EASJ, which enhanced the anomalous westerly winds to the north of the anticyclone. Moreover, the WPSH extends westward during strong TP heating years. With the cooperation of high pressure and moisture, there was an anomalous meridional circulation pattern with ascending motion in North China and descending motion in the YHRB, accompanied by reduced cloud cover and increased insolation in the YHRB, leading to further intensification of local heatwaves in 2022. This study demonstrates the significant role of TP thermal anomaly in YHRB heatwaves.