China's Yangtze River basin is becoming the super heatwave centre in the East Asian monsoon regions

Different from the general heatwaves that mainly occur in southeastern China, the super heatwaves in China are concentrated mostly in the mid–lower reaches of the Yangtze River basin. Daily maximum temperature data over land from CPC/NOAA revealed that the basin has become the centre with the highest frequency increase of super heatwaves in the East Asian monsoon regions in the 21st century. Further analyses also indicted that the extent of super heatwaves in the basin has a much higher increasing rate than that of general heatwaves by using running thresholds. The westward extension of the western Pacific subtropical high (WPSH) plays the most dominant role. Statistical results suggested that a 10-gpm increment of the geopotential height (GPH) over the basin leads to a 0.43°C increase in the regionally averaged maximum temperature. Additionally, spatial extent of the super heatwave may expand by approximately 4%. In contrast to the stable eastern boundary of the North Africa high, the western boundary of the WPSH has significantly expanded westward in the 21st century. This expansion has led to the enhancement of the GPH over the Yangtze River basin, resulting in the super heatwave centre due to the heat-dome effect. Projections from 29 Coupled Model Intercomparison Project Phase 6 (CMIP6) models under moderate greenhouse gas emission scenario (SSP2-4.5) suggest that the GPH over the Yangtze River basin will continue to strengthen throughout the 21st century. This implies that the Yangtze River basin will continue to be the centre of super heatwaves in East Asia monsoon region.