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

Lin Chen,Bin Zhou,Mingyue Liu,Weidong Man

doi:10.3390/rs13214268

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.

Highlights

Urban areas comprise approximately 5% of the total surface of the Earth [1]
In the last 20 years, expansion slowed in Shangcheng, Xiacheng, Jianggan, Gongshu and Binjiang districts, impervious surfaces expanded with an increasing growth rate of 6.11% in Hangzhou City (Figure 4)
The centroid movement revealed that urban expansion was more rapid in the southeast (Figure 8), which resulted from the extensive urban growth in the flat terrain of southeastern Hangzhou City, such as in Xiaoshan District and the east of Yuhang District

Summary

Introduction

More than half of the human population lives in cities [2] This arrangement has produced a series of global environmental problems due to the replacement of natural land cover with impervious surfaces [3]. Heat stress due to these local modifications on land-use types, radiative forcing, and air circulation is one of the most severe challenges facing urban residents [6,7]. This phenomenon is traditionally called the urban heat island effect, and induces the growth of energy consumption, especially in summer. This phenomenon has a strong impact on the local air quality and greenhouse gas emissions [8,9]

Methods

Results

Discussion

Conclusion