An integrated framework for jointly assessing spatiotemporal dynamics of surface urban heat island intensity and footprint: China, 2003–2020
Yuan Wang, H.G. Wang, Fei Yao, Rudi Stouffs, Jiansheng Wu
Abstract
An urban heat island (UHI) refers to a metropolitan area significantly warmer than its rural surroundings. Accurately quantifying UHI intensity (UHII) relies on selecting appropriate rural areas, which lack a universal definition. A crucial aspect in UHII quantification is considering the spatial extent of the UHI effect, known as its footprints (UHIFP). Here, we propose a framework to jointly estimate both UHII and UHIFP, integrating the latter into the former. Our approach involves creating 12 equal-area buffer zones around each urban boundary and initially selecting the three farthest zones as rural areas. Using a seamless 1-km daily land surface temperature dataset on Google Earth Engine, we constructe exponential decay models to characterize the temperature variations along the urban-area gradient of each city and and to extract UHIFP from these models. The results reveal that the average UHIFP during daytime and nighttime are 2.6 and 2.7 times of the urban size, respectively, predominantly located before the three farthest buffer zones, thereby verifying the effectiveness of the selected rural areas for accurate UHII calculations. This framework is critical for evaluating the risks associated with extreme heatwaves and heat stress. It also provides suggestions for UHI mitigation measures from an urban-rural gradient perspective.