A Multiscale Thermal Environment Network Framework for Urban Agglomerations: Changes from 2000 to 2020 and Planning Insights from the Hangzhou Bay Region

Abstract

Against the backdrop of climate change and rapid urbanization, the urban thermal environment (UTE) in urban agglomerations continues to deteriorate, posing a growing challenge to regional sustainability. Network-based approaches have increasingly been applied to UTE studies, but most studies have focused on a single spatial scale, with limited attention to thermal connectivity at different scales. Therefore, this study used land surface temperature (LST) data from 2000, 2010, and 2020 together with the Patch-generating Land Use Simulation (PLUS) model and circuit theory to construct a multiscale UTE network framework for the Hangzhou Bay urban agglomeration. A cooling network was constructed at the urban-agglomeration scale and a heat network within the national-level urbanized zone, and temporal changes in each scale-specific network were examined across the three study periods. The results showed that: (1) Low-temperature areas remained concentrated in the southwestern mountains and major water bodies but continued to shrink, whereas high-temperature areas expanded and gradually coalesced across areas surrounding Hangzhou Bay, with more pronounced clustering within the national-level urbanized zone. The total area of cold sources decreased from 3249.76 to 2411.50 km2, whereas that of heat sources increased from 1061.32 to 2896.28 km2. (2) At the urban-agglomeration scale, the mean corridor length of the cooling network increased from 12.23 to 17.41 km, while the α, β, and γ indices declined continuously; within the national-level urbanized zone, the mean corridor length of the heat network decreased from 17.85 to 10.30 km, with all three indices reaching their highest values in 2020. (3) Cooling-network barriers spread from cold-source clusters into transitional areas linking cold sources with urbanized areas, whereas heat-network pinch points shifted from established heat-source clusters to emerging ones. This study provides a multiscale network perspective on thermal connectivity in urban agglomerations and offers spatial evidence for cross-regional thermal-environment management and climate-adaptation planning.