Diversified evolutionary patterns of surface urban heat island in new expansion areas of 31 Chinese cities

As a hot area of population inflow in the process of urbanization, the urban expansion area faces rapid growth of surface urban heat island (SUHI). However, the multi-dimensional evolutionary characteristics of SUHI in urban expansion areas are still unclear. Through analyzing the evolution of SUHI range ratio, mean intensity and maximum intensity, in this study we identified the comprehensive evolutionary pattern of summer SUHI in urban expansion areas of 31 major cities in China during 2000-2018, and further investigated the corresponding dominant influencing factors. The results showed that the SUHI range and intensity in urban expansion areas exhibited a significant increasing trend in 81% and 71% of the cities respectively during the summer daytime. The cities with declining SUHI range and intensity were distributed in northwestern high-altitude areas with low economic level, while the cities with dominant increases in the SUHI range were distributed in eastern low-altitude areas with high economic level. Climate conditions and population distribution were the dominant influencing factors of intensity-dominated increasing and balanced increasing types, respectively. The intensity and range two-dimensional increasing type had experienced the most severe SUHI growth, with large proportion of secondary industry as the main influencing factor. This study highlighted the importance of multi-dimensional characteristics of SUHI evolution, which provided a new insight to understand SUHI change in urban expansion areas and associated mitigation measures.