Regional patterns and trends of compound hot extremes in mainland China: a new objective approach

Abstract

Compound hot extremes (CHEs) are receiving increasing attention due to their significant impacts on human health, ecosystems, and society compared to individual hot days or nights. While previous studies have focused on the characteristics of CHEs at individual points or stations, assessments of features for regional CHEs (RCHEs), which have a specific impact area and duration, are still lacking. This study aimed to investigate the climatic characteristics of RCHEs in mainland China by applying an objective identification technique for regional extreme events based on a compound index. The results show that 379 RCHEs were identified during 1961–2020, most of the events had a duration of 5–11 d and a maximum impacted area of approximately 460 104 km2. Long-duration RCHEs were found to have vigorous extreme intensity and large maximum impacted area. The middle and lower reaches of the Yangtze River were most susceptible to RCHEs, while the Yellow River Valley had the most robust positive trend of frequency for RCHEs, suggesting a significant risk of compound temperature disasters in this region. Furthermore, RCHEs in mainland China showed significant increasing trends in several aspects, such as annual frequency, integrated index, and single indices (e.g. duration, accumulated intensity, accumulated impacted area, and extreme intensity). These upward trends were accompanied by evident interdecadal variations, with low values before 1992 and high values after 1992. This study provides valuable insights into understanding and monitoring CHEs in China from the perspective of regional extremes.