Anthropogenic exacerbations of summer-autumn compound dry-hot severity in the middle and lower reaches of the Yangtze River

The middle and lower reaches of the Yangtze River (MLRYR), one of the most densely populated and economically developed regions in China, have suffered several severe compound dry-hot events (CDHEs) during the summer-autumn seasons in recent decades. However, it is unclear for spatiotemporal evolutions in this season’s CDHE severity and anthropogenic influence on them. Here, we calculated the Standardized Compound Event Indicator (SCEI) to quantify the CDHE severity during the summer-autumn season (August to November). During the past twelve decades, significant decreases in SCEI (–0.81 per century) in MLRYR have been found in observations, with the dependence of SCEI on low precipitation shifting to high temperatures. Temperatures change primarily contribute to the changes in SCEI with (82.3 %) or without (57.1 %) considering the effects of long-term warming. Quantitative detection and attribution results show that during 1901–2020, 86.7 % of the observed decrease in SCEI in MLRYR can be attributed to anthropogenic warming. In a warmer future, SCEI is projected to dramatically decrease before global warming reaches 3.5 °C above the preindustrial level. After exceeding 3.5℃, the CDHE severity in MLRYR is projected to stay at a new-normal serious level which exceeds the most severe CDHEs (such as in 2019 and 2022) during the past century. This new-normal serious level could be avoided if the global warming level is limited to around 2 °C. Early action to achieve the 1.5 °C or 2 °C temperature goal can therefore markedly reduce the likelihood that MLRYR would be exposed to record-shattering CDHEs and related impacts.