Investigating the influence of morphologic and functional polycentric structures on urban heat island: A case of Chongqing, China

Polycentric urban structures are widely regarded as solutions to mitigating urban heat islands (UHI). However, few studies clarified the influences of morphological and functional polycentrism on UHI. Using Chongqing as the case study, we revealed the spatial pattern of UHI based on ECOSTRESS images and morphological/functional polycentrism based on multi-source data. Then, we quantified the spatial and nonlinear effects of polycentric structures on UHI using spatial regressions and XGBoost-SHAP methods. The results showed that polycentric structures exhibit spillover and nonlinear effects on local heat variation. Building volume alleviated UHI in the urban core, signifying a substantial shadowing effect in a mountainous setting. Population density positively but weakly affected local UHI among urban centers. Facility mixture positively affected UHI mainly in facility-abundant subcenters within the effective range between 0.5 and 1.0. As a functional factor, functional linkages exerted positive effects mainly in the urban cores where the degree centrality is larger than 1,500 while exhibiting negative correlation in the peripheral subcenters, suggesting the cooling effects by dispersing functions in the urban core. These findings help mitigate UHI by targeting measures for optimizing polycentric structures.