Escalating population and land exposure to human-perceived heatwaves in China: Insights from excess heat factor

Current assessments of human-perceived heatwaves (HPHWs) primarily incorporate the synergistic effects of temperature and humidity but largely neglect the influences of local antecedent heat conditions and human acclimatization, limiting the comprehensive evaluation of HPHW changes. Using hourly reanalysis products and gridded population data, we systematically compare three HPHW definitions and further apply a modified excess heat factor (EHF) framework to characterize the long-term spatiotemporal evolution of HPHWs and associated extreme heat exposure across three seasons (excluding winter) in China. The results show that most HPHW metrics exhibit opposite directional changes between the periods of 1961−1984 and 1985−2022. Spatially, South and Southwest China experience more substantial rises in HPHW occurrence, total days, and duration. The most pronounced intensification of HPHW events is found in Northeast China, and the onset of the first yearly HPHW advances most markedly in North China. At the national scale, the population-weighted HPHW frequency (∼2.49 d per decade per person) increases at a faster rate than its area-weighted counterpart (∼1.44 d per decade per unit of land area), indicating the disproportionate effect of HPHW occurrence on populated areas. Jianghuai region exhibits the most notable growth in both mean (∼4 million people per decade) and maximum (∼50 million people per decade) population affected by extreme heat. Regarding mean and maximum land area exposed to extreme heat, the most substantial increases occur in Jianghuai region and South China, at approximately 9 thousand km 2 and 85 thousand km 2 per decade, respectively. Our findings enhance the understanding of HPHW variations across China and demonstrate the necessity to mitigate escalating dangers of heat stress in a warming climate.