Spatiotemporal Evolution and Component Contributions to Urban Heat–Humidity Risk Changes in Sichuan Province, China, from 2000 to 2024

Compound hot–humid events are placing increasing pressure on urban health and land-use governance as climate warming and urban expansion continue. This study examined urban built-up areas in 21 prefecture-level cities and prefectures of Sichuan Province for 2000, 2005, 2010, 2015, 2020, and 2024. Using the IPCC hazard–exposure–vulnerability framework, ERA5-Land, MODIS land-cover, GHSL population, and socioeconomic data were combined to construct the Humid Heat Hazard Index (HI), Population-Density Exposure Index (EI), Socioeconomic Vulnerability Index (VI), and Comprehensive Urban Heat–Humidity Risk Index (HHRI). Contribution decomposition, LISA, and standard deviation ellipse analysis were then used to examine risk changes and spatial patterns. The mean HHRI decreased from 0.42 to 0.24, but rebounds appeared in 2010 and 2024. HI varied strongly among years and drove short-term risk changes, EI declined continuously, and VI dropped from 0.87 to 0.30, making it the main factor behind long-term risk reduction. Higher-risk areas were mainly located in southern Sichuan, southeastern Sichuan, and the central-eastern Sichuan Basin. LISA results showed high-risk clusters in basin cities and low-risk clusters on the western Sichuan Plateau. The standard deviation ellipse remained mostly within the basin and followed the basin urban belt. Future adaptation should combine public-service improvement with heat warnings, cooling services, and emergency preparedness.