Escalating population and land exposure to human-perceived heatwaves in China under a warming climate

Anthropogenic warming has significantly exacerbated heatwaves (HWs) globally, posing severe threats to public health. In light of the insufficiency of using solely ambient temperature to assess human heat stress, previous studies identified human-perceived HWs (HPHWs) by considering the synergistic effects of temperature and humidity. However, the limited attention given to the influence of local antecedent heat conditions and human acclimatization hampers the comprehensive evaluation of HPHW changes. Through a systematic comparison of three HPHW definitions, this study employs the Excess Heat Factor (EHF) to examine the long-term spatiotemporal variations in HPHWs across three seasons (excluding winter) in China, as well as the associated extreme heat exposure. The results show that most HPHW metrics exhibit opposite directional changes between the periods of 1961−1984 and 1985−2022. Regionally averaged, South and Southwest China experience more substantial rises in HPHW occurrence, duration and frequency. The most pronounced intensification of HPHW events is found in Northeast China, and the onset of the first yearly HPHW advances most significantly in North China. At both national and sub-regional scales, the population-weighted HPHW frequency increases at a faster rate than its area-weighted counterpart, indicating the disproportionate effect of HPHW occurrence on populated areas. Jianghuai and South China generally undergo the most notable increases in both mean and maximum population/land area affected by extreme heat. Our findings contribute to a better understanding of HPHW changes across China and highlight the urgent need for adaptation strategies to mitigate escalating dangers of heat stress in a warming climate.