Relative Contributions of Large-Scale Atmospheric Circulation Dynamics and Anthropogenic Warming to the Unprecedented 2022 Yangtze River Basin Heatwave

The unprecedented 2022 Yangtze River Basin (YRB) heatwave is a threat to human society and natural ecology, so the understanding of its underlying drivers is critical to regional climate adaptation and resilience. Here we conducted a multi-method attribution analysis on the contribution of atmospheric circulation change and anthropogenic impacts to the occurrence probability and intensity of this extreme heatwave. Based on the nonstationary statistical analysis, the 2022 YRB heatwave is a 1-in-900-year event and a 1-in-110-year event with and without considering the 2022 YRB heatwave in the fitting, respectively. The large-scale meteorological condition analysis shows that the 2022 YRB heatwave is featured with an anomalous high-pressure system that favors a hot and dry atmospheric column, overlaid by anomalous subsidence and clear skies which leads to warming and greater solar heating. The ensemble constructed circulation analogue analyses show that the circulation anomaly fails to explain the observed 2022 YRB SAT anomalies fully. Specifically, 46% (0.132 +/- 0.027 degrees C decade-1) of the observed SAT trend during 1979-2022 (0.290 +/- 0.048 degrees C decade-1) is caused by anthropogenic warming and the associated thermodynamic feedback, while the remaining 54% (0.157 +/- 0.038 degrees C decade-1) of the trend is caused by changes in the large-scale atmospheric circulation. Our findings on changes in atmospheric circulation patterns associated with YRB heatwave and anthropogenic contributions to YRB heatwave could provide valuable information for climate adaptation and mitigation strategies in the context of a warming climate. Heatwaves are major climate extremes in the context of global warming, which have inverse effects on human health, food and energy production, and ecosystems. The 2022 heatwave in the Yangtze River Basin (YRB) sets a new record in observational history with its extreme intensity, long duration, and widespread affected areas. The 2022 YRB heatwave is too exceptional to be possible without anthropogenic warming, which is a 1-in-900-year event and a 1-in-110-year event, respectively, with and without considering it in the nonstationary statistical fitting. An anomalous and prolonged high-pressure system predominated the evolution of the 2022 YRB heatwave, which favors anomalous subsidence and clear skies, leading to hot and dry atmospheric conditions. Next, we applied an ensemble circulation constructed analogue approach to separate the contributions of large-scale circulation changes and anthropogenic warming in generating the 2022 heatwave. The results reveal that circulation dynamics can only partially explain the 2022 event. When historical changes are taken into account, the changes in large-scale circulation and anthropogenic warming, respectively, can account for 54% and 46% of the observed summer surface air temperature anomalies in the YRB region. The 2022 Yangtze River Basin (YRB) heatwave, linked to anomalous circulation backgrounds, set unprecedented records for surface air temperature (SAT) The atmospheric circulation anomalies alone cannot fully explain the SAT anomalies during the 2022 YRB heatwave The variation in atmospheric circulation and anthropogenic warming contributed nearly equally to the historical SAT trend of YRB