More extreme-heat occurrences related to humidity in China

The co-occurrence of day and night compound heat extremes has attracted much attention because of the amplified socioeconomic and human health impacts. Based on ERA5 hourly reanalysis data, this study characterized and compared extreme day–night compound humid-heat/high-temperature events (CHHEs/CHTEs) in China as well as the associated impacts. Results indicated that the spatial patterns of summer mean extreme CHHEs are consistent with those of extreme CHTEs, except in northwestern China. A greater magnitude of these two types of events dominates over southern China, but the high-frequency centers are mainly observed over northern China. Significant increasing trends in frequency are captured nationwide, but with much stronger trends detected in northern and western China. Further analysis shows that the anomalies of humidity play a more important role than those of temperature in the occurrence of extreme CHHEs in most parts of China, but particularly in eastern regions. Since 1961, the human population and land areas of China have experienced strongly increasing compound heat extremes, with a faster rate of exposure to extreme CHHEs than to extreme CHTEs. This study highlights the importance of understanding regional changes in humidity when considering heat stress in the future.