Assessing spatiotemporal characteristics of urban heat islands from the perspective of an urban expansion and green infrastructure

Urban heat island (UHI) effect is a common urban problem in the process of rapid urbanization. It is also widely considered as one of the most critical global problems in the 21st century. The UHI effect poses a severe challenge to the sustainable development strategy of cities, the living environment of urban residents and the livability of cities. In the context of urban planning and landscape design, how to mitigate the UHI effect and how to help urban residents adapt are one of research topics on urban thermal environments. With Landsat thermal sensor images, this study retrieved urban land surface temperature (LST), and revealed spatiotemporal characteristics of surface urban heat island (SUHI) effect from the perspective of urban expansion and urban green infrastructure. The results indicate that the Hangzhou city SUHI effect was prominent. From 1990 to 2010, the high-grade SUHI effect area tended to move to the north, while from 2010 to 2018, the high-grade SUHI effect area tended to move to the south, which was consistent with the direction of urban expansion. Urban edge-expansion led to continuous expansion of urban scope, and urban center was dominated by infilling expansion. The core area of green infrastructure in the city center was small, and the ecological corridor was reduced, which intensified the SUHI effect of the city center. In different time periods, the relationship between SUHI effect, urban expansion and urban green infrastructure was different. The analysis results derived from this study were considered valuable for urban planners and landscape designers to alleviate the SUHI effect, build an ecological civilization city and construct a "livable city".