Assessment of heat exposure risk for urban populations and spatio-temporal patterns: A perspective of urban functional zones in Xi'an, China

Heat exposure risk has obvious spatio-temporal dynamics in cities, especially in urban functional zones (UFZs), which have significant variations in human activities. However, previous studies have overlooked the assessment based on UFZs. This study integrated remote sensing images and points of interest data to identify the UFZs in Xi'an, China. It also combines land surface temperature data with population distribution data to measure the risk of heat exposure for urban residents at the UFZ level. The results indicated that the top five UFZs, ranked by average risk level, were the business office zone, general business zone, residential zone, science and education zone, and public service zone. The proportion of the study area categorized as ultrahigh and high risk was 2.5% and 3.4%, respectively. These areas were mainly concentrated in the central region within the second ring road. The areas with a higher risk during the day were mainly distributed along the central axis of the city, while the areas with a higher risk at night were mostly concentrated between the second and third ring roads of the city. These findings have significant implications for urban planning and management in terms of mitigating and adapting to the risk of heat exposure.