Polycentric urban development and urban thermal environment: A case of Hangzhou, China

Polycentric urban structure has become popular worldwide, including in China. Previous studies revealed that polycentricity can remediate certain environmental problems; however, few studies have focused on how polycentricity affects the urban thermal environment. Using remote sensing data for the nighttime light and surface temperature, this study first explored the dynamics of polycentric urban development and thermal environment in Hangzhou during 2000-2010. Then their relationship was investigated in both morphological and functional dimensions. It was observed that from 2000 to 2006, Hangzhou experienced rapid polycentric development, especially in the functional dimension; however, this trend slowed down during 2006-2010. With the expansion of hot and medium-hot landscapes, the area with higher surface temperature enlarged notably, and warming trends were more significant in the suburbs than in the urban core. Polycentric urban development in both morphological and functional dimensions was positively correlated with the deterioration of the thermal environment. The regional differences in the urban thermal environment can be attributed to the distinctive functional orientations and development patterns of (sub)centers. Further, industrial sub-urbanization could be the underlying reason for the positive correlation because of its consistent distributions with the newly-expanded hot landscape and more contiguous hot landscape caused by the single land use pattern in industrial areas. Two policy implications about polycentric planning and landscape composition and configuration in industrial areas were proposed to mitigate the effect of urban heat island. The findings in this study are conductive to cities whose polycentric urban development is also industrial-based.