Exploration of urbanization characteristics and their effect on the urban thermal environment in Chengdu, China

As rapid urbanization has drastically and widely altered the Earth's surface, urbanization has become an important contributor to changes in land surface temperature (LST) and the urban thermal environment, which has increasingly become a focus of urban ecologists and environmentalists. The present study used one of the fastest-growing cities in Southwest China, Chengdu city, as an example to explore the urbanization pattern and its effects on surface urban heat islands (SUHIs). To analyze the temporal and spatial characteristics of urban expansion, land use or land cover (LULC) images were classified using a support vector machine (SVM) classifier from Landsat images in 2004–2018, with an overall accuracy of 0.94 and kappa coefficient of 0.90. According to the spatiotemporal LULC changes, Chengdu city expanded at a rapid pace from 80.43 km2/a to 210.50 km2/a in 2004–2018, with an increasing reliance on vegetation area conversion. Spatially imbalanced expansion also occurred. The gravity center moved toward the southeast overall, and peripheral circle districts were the main force of Chengdu's urban expansion compared to the slow-expanding core districts. An allometric model was used to analyze the urbanization pattern, and the results indicated that expansion in Chengdu city was far in excess of its corresponding population growth. The SUHI effect in Chengdu mostly deteriorated over time, and SUHI deterioration closely correlated with the urban expansion area rate and expansion intensity. Therefore, excess urbanization at the expense of vegetation decrease damages the urban ecological environment and accelerates SUHI effects, which threaten habitat health and living comfort.