Assessing China's Hillside Urban Expansion and Its Urban Thermal Environmental Impacts Using Multisource Data

Global urban expansion presents a clear upward trend, reshaping urban socioeconomic frameworks and environmental dynamics. This study developed a multisource classification framework to accurately identify hillside urban expansion (HUE) across China, a region undergoing rapid transformation amidst diverse mountainous landscapes. Based on this foundation, we investigated the spatiotemporal evolution patterns of HUE and analyzed its influence on the urban thermal environment (UTE). Results show that leveraging a developed classification framework, the identified HUE exhibits stronger edge detail capture and higher patch integrity, achieving an overall accuracy of 78%. HUE in China shows a general trend of spatial expansion, predominantly dominated by low hillside urban expansion (LC) and moderate hillside urban expansion (MC). The relationship between HUE and land surface temperature (LST) is predominantly positive and exhibits variability. Specifically, LC maintains a stable positive correlation with LST, whereas MC and heavy HUE display varying relationships with LST. Our study presents an effective way for accurately identifying and evaluating HUE and its UTE effects. It provides a scientific reference for land use and spatial governance studies and holds notable implications for the progress evaluation with the UN's Sustainable Development Goals by 2030, particularly SDG 11 (Sustainable Cities).