The influence of urban form on surface urban heat island and its planning implications: Evidence from 1288 urban clusters in China

There is a growing demand for urban form optimization to mitigate urban heat island (UHI) effect. Nevertheless, how UHI responds to various urban morphological patterns is still limitedly understood, especially for cities in developing countries. Here, based on 1288 urban clusters identified automatically across China, we created a consistent analytical environment to recognize both homogeneity and heterogeneity of the relationship. Specifically, urban form was characterized from aspects of size, shape, and centrality, respectively measured using metrics of urban size, area-weighted mean shape index (AWMSI) and dispersion index (DI), entropy and Moran's I. Then, relationships between the metrics and surface UHI (SUHI) were modelled using the ordinary least squares (OLS). Results reveal that in nighttime when stronger relationships were observed than in daytime, centrality, a feature of intra-urban development structure largely neglected by previous studies, dominated as the most influential aspect. The relationships also varied across climate zones. A two-step OLS regression further reveals them to be size-dependent. As city expanded, the rising shape irregularity created a cooling impact, while the rising centrality leaded to urban warming. Overall, this study suggests that, in addition to controlling urban expansion, the optimal urban form for SUHI mitigation is moderately dispersed, polycentric, and decentralized.