Quantitative attribution of 2013 and 2022 extremely hot events in China: Insights from a climate feedback-response perspective

Abstract Unprecedented extremely hot events occurred in eastern China during August 2013 (EH13) and August 2022 (EH22). The physical factors responsible for the recent record-breaking extremely hot events, particularly their relative contributions to different events, are poorly understood. Using an updated version of the climate feedback–response analysis method (CFRAM-A), we quantitatively attribute these two events to several external forcing and internal processes and identify common and distinct drivers in both events. Results show that reduced clouds provide the largest positive contribution primarily through modulating shortwave radiation, but water vapor plays different roles in the two events. Both atmospheric dynamics and aerosol processes have positive effects on the surface warming, but surface processes (surface heat flux changes) exert overall negative influences. The temperature budget analysis indicates that the rapid warming for EH13 explained by atmospheric dynamics is attributed to horizontal advection and adiabatic warming. For EH22, the positive contributions of atmospheric dynamics are largely dominated by adiabatic and diabatic warming. An excess of water vapor contributes positively to EH22 through longwave radiation effects, but the anomalous reduction of water vapor during EH13 has opposing effects. Moreover, the aerosol-related processes are detected to exhibit strong warming for EH22, but their impacts on EH13 are comparatively weak. This feature highlights a significant reduction in aerosols due to effective emission reduction policies implemented in China, potentially exacerbating the severity of subsequent extremely hot events. The quantitative attribution based on the CFRAM-A provides crucial insights for an in-depth understanding of the formation mechanisms underlying extremely hot events in China. Significance Statement Frequent occurrences of extremely hot events significantly impact local agriculture, water resources, ecosystems, and human health. Here, we employ an updated version of the climate feedback–response analysis method (CFRAM-A) to diagnose the influences of different dynamic and radiative processes during two unprecedented extremely hot events in 2013 (EH13) and 2022 (EH22). The overall surface warming pattern associated with the two events can be predominantly attributed to the combined effects of anomalous clouds, water vapor, aerosols, atmospheric dynamics, and surface processes. Clouds, aerosols, and atmospheric dynamics all contribute positively to surface warming. An excess of water vapor exerts a beneficial influence on EH22, resulting in intensified nighttime heat waves, whereas the anomalous reduction of water vapor during EH13 produces an opposing effect. Clouds and atmospheric dynamics processes make notable positive contributions to both events. Changes in water vapor and aerosols contribute significantly to the warming observed during EH22, while these effects are not detected for EH13. The mechanisms of several key processes influencing the extremely hot events are further elucidated. Based on the quantitative diagnosis derived from CFRAM-A, this study offers valuable insights into the mechanisms driving the changes of extremely hot events in China.