Quantifying the extremity of 2022 Chinese Yangtze River Valley daily hot extreme: fixed or moving baseline matters

Abstract

In 2022, an extreme heatwave struck the Yangtze River Valley (YRV) of China. Existing studies have highlighted its record-breaking magnitude by comparison with historical records using a fixed baseline. However, the quantification of extremity relies on the choice of baseline. While using fixed baseline allows us to understand the changes in extremes with the background warming, the use of moving baseline quantifies the extremity relative to recent climatology, and thus, takes into account the societal adaptation capability to global warming. Here, we revisit the 2022 heatwave in China and examine the extremity of daily hot extreme by comparing the two methods. Using a fixed baseline, daily hot extremes occurred in 2022 in the upper and middle reaches of YRV broke records since 1971. Nevertheless, using a moving baseline, daily hot extremes broke records only in the upper reaches (Sichuan Basin). In addition, it is not the most extreme event (measured by standard deviation anomalies), as China has experienced ~ 13 more extreme events since 1971. The future projections show that, when using fixed baseline, 2022 Sichuan basin like extreme will occur every 2-12 years in 2081-2100 period under high-emissions scenarios, and will sweep China. Approximately 2-25% of continental China will experience daily hot extreme with magnitude exceeding 5 standard deviations (SDs). Nevertheless, the projected changes based on moving climatology are weak, indicating that if we take measures to enhance our adaptability to background warming, the risks associated with hot extremes would be reduced in China.