Unraveling the association between the urban polycentric structure and urban surface thermal environment in urbanizing China

The urban surface thermal environment has greatly changed in China's accelerated urbanization process, which is closely related to urban eco-security, socioeconomic activities, and residents' comfort and health. Recent studies have focused on the effects of urban form optimization on the urban surface thermal environment, but few have been conducted from an urban polycentric structure perspective. This paper quantified the association between the urban polycentric structure and urban surface thermal environment of Chinese major cities at the prefecture level and above in 2015, 2010 and 2003 using spatial regression. The results revealed that (1) no significant association were found between the urban polycentric structure and the average land surface tem-perature (LST). (2) Both the increase in the urban center number (N) and the degree of polycentricity (POLY) are conducive to a uniform LST distribution and an increase in the number of high-temperature patches. In 2003, 2010 and 2015, the effect coefficients of POLY and N on the standard deviation of LST ranges from-0.126 to 0.102 and from-0.132 to-0.094, respectively, and on the number of different high-temperature patches ranges from 0.067 to 0.197 and from 0.098 to 0.502, respectively. (3) The increase in the degree of polycentricity is correlated with smaller high-temperature patches. In 2003, 2010 and 2015, a one-unit increase in POLY was associated with a 0.097-to 0.124-unit decrease in the average area of different high-temperature patches. The findings suggest that an urban polycentric structure is conducive to forming smaller and more fragmented high-temperature patches, which contributes to a uniform LST distribution and exerts positive effects on alleviating urban heat aggregation. This work enriches the research on the ecological performance of urban polycentric structure and provides a preliminary but effective basis for the formulation of polycentric development strategies from an urban surface thermal environment improvement perspective.