Influence of Impervious Surface Area and Fractional Vegetation Cover on Seasonal Urban Surface Heating/Cooling Rates

Youshui Zhang,Yu Li,Heiko Balzter

doi:10.3390/rs13071263

Abstract

The urban thermal environment is impacted by changes in urban landscape patterns resulting from urban expansion and seasonal variation. In order to cope effectively with urban heat island (UHI) effects and improve the urban living environment and microclimate, an analysis of the heating effect of impervious surface areas (ISA) and the cooling effects of vegetation is needed. In this study, Landsat 8 data in four seasons were used to derive the percent ISA and fractional vegetation cover (FVC) by spectral unmixing and to retrieve the land surface temperature (LST) from the radiative transfer equation (RTE). The percent ISA and FVC were divided into four different categories based on ranges 0–25%, 25–50%, 50–75%, and 75–100%. The LST with percent ISA and FVC were used to calculate the surface heating rate (SHR) and surface cooling rate (SCR). Finally, in order to analyze the heating effect of ISA and the cooling effect of vegetation, the variations of LST with SHR and SCR were compared between different percent ISA and FVC categories in the four seasons. The results showed the following: (1) In summer, SHR decreases as percent ISA increases and SCR increases as FVC increases in the study area. (2) Unlike the dependence of LST on percent ISA and FVC, the trends of SHR/SCR as a function of percent ISA/FVC are more complex for different value ranges, especially in spring and autumn. (3) The SHR (heating capacity) decreases with increasing percent ISA in autumn. However, the SCR (cooling capacity) decreases with increasing FVC, except in summer. This study shows that our methodology to analyze the variation and change trends of SHR, SCR, and LST based on different ISA and FVC categories in different seasons can be used to interpret urban ISA and vegetation cover, as well as their heating and cooling effects on the urban thermal environment. This analytical method provides an important insight into analyzing the urban landscape patterns and thermal environment. It is also helpful for urban planning and mitigating UHI.

Highlights

This study shows that our methodology to analyze the variation and change trends of surface heating rate (SHR), surface cooling rate (SCR), and land surface temperature (LST) based on different impervious surface areas (ISA) and fractional vegetation cover (FVC) categories in different seasons can be used to interpret urban ISA and vegetation cover, as well as their heating and cooling effects on the urban thermal environment
As the two main urban land cover types, the composition and configuration of ISA and vegetation patches affect the spatial distribution patterns and magnitude of LST, and the LST increases with increasing percent ISA and decreases with increasing FVC
Subpixel ISA and FVC were extracted from Landsat data by fully constrained least squares (FCLS), and the accuracy was assessed by testing areas using very-high-resolution remotely sensed imagery

Summary

Introduction

Urbanization, with the transformation of natural landscapes to impervious surface area, can result in environmental degradation and human and social issues, such as urban heat island (UHI) effects, air pollution, climate change, and adverse effects on human health and well-being [1,2,3]. Among the urban environmental problems, the UHI phenomenon can be evaluated by comparing the land surface temperature (LST) values in urban and rural environments. The LST is usually retrieved from thermal infrared (TIR) remote sensing data [4,5]. Advances in remote sensing have enabled the use of satellite data at various spatial and temporal resolutions for estimating LST over entire urban regions, making such data superior to point observations of LST on the ground.

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