Assessing urban population exposure risk to extreme heat: Patterns, trends, and implications for climate resilience in China (2000-2020)

Urban residents face serious thermal health risks from extreme heat owing to the cumulative effects of urbanization and climate warming. However, the patterns of urban populations exposed to extreme heat and urban extreme heat exposure risks (UEHER) require clarification in China. We determined urban extreme heat and the exposed populations for land surface temperature (LST) in 320 cities from 2000 to 2020 by setting thresholds and assessed the UEHER in China through the "Hazard-Exposure-Vulnerability" framework. Our findings indicated an average extreme LST threshold of 35.24 degrees C, varying from 29.32 degrees C to 47.79 degrees C. Higher extreme LST thresholds were mainly concentrated in Northwest China and developed cities. From 2000 to 2020, the extreme heatexposed areas have increased by approximately 27.8 km(2), equivalent to an average of approximately 321.3 soccer fields per year. The urban population exposed to extreme heat (UPEEH) in China has increased by approximately 115 million in the past 20 years, mainly in more developed cities, especially in eastern and northern China. Notably, the proportion of the UPEEH has decreased more rapidly in the east region. The UEHER index increased 52.5 % over 20 years, with 97.19 % of the cities having a worsening trend. Medium-developed and high-population density regions faced the dual risk of a high UEHER and more rapid increase in extreme heat. In contrast, less-developed regions faced the dual problems of high UEHER and low gross domestic product (GDP). Understanding vulnerable and prioritized areas of urban heat exposure will provide information for the development of adaptive policies that enhance urban climate resilience.