Landsat-Based Monitoring of the Heat Effects of Urbanization Directions and Types in Hangzhou City from 2000 to 2020

Abstract

Rapid urbanization has produced serious heat effects worldwide. However, the literature lacks a detailed study on heat effects based on the directions and types of urban expansion. In this work, a typical city with an extremely hot summer climate, Hangzhou, was selected as a case study to determine the relationships between the urban heat-effect dynamics and spatiotemporal patterns of impervious surface expansion. Based on long-term Landsat imagery, this study characterized the spatiotemporal patterns of urban expansion and normalized surface temperatures in Hangzhou City from 2000 to 2020 using object-based backdating classification and a generalized single-channel algorithm with the help of a land-use transfer matrix, expansion index, and spatial centroids. Relevant policies, industries, and traffic networks were discussed to help explain urban expansion and thermal environment changes. The results demonstrated that in 2020, the area of impervious surfaces covered 1139.29 km2. The majority of the gains were in farmland, water, and forests, and the annual growth rate was 32.12 km2/year beginning in 2000. During the expansion of impervious surfaces, the city warmed at a slower rate, and more thermal contributions came from sub-urban areas. The southeast-oriented expansion of impervious surfaces was the key reason for the spatiotemporal dynamics of the urban heat effects. The dominant urban edge expansion intensified the local heat effects. This research provides a Landsat-based methodology for better understanding the heat effects of urban expansion.