A Methodology for Comparing the Surface Urban Heat Island in Selected Urban Agglomerations Around the World from Sentinel-3 SLSTR Data

José Antonio Sobrino,Itziar Irakulis

doi:10.3390/rs12122052

José Antonio Sobrino, Itziar Irakulis

Open Access

https://doi.org/10.3390/rs12122052

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Abstract

Retrieval of land surface temperature (LST) from satellite data allows to estimate the surface urban heat island (SUHI) as the difference between the LST obtained in the urban area and the LST of its surroundings. However, this definition depends on the selection of the urban and surroundings references, which translates into greater difficulty in comparing SUHI values in different urban agglomerations across the world. In order to avoid this problem, a methodology is proposed that allows reliable quantification of the SUHI. The urban reference is obtained from the European Space Agency Climate Change Initiative Land Cover and three surroundings references are considered; that is, the urban adjacent (Su), the future adjacent (Sf), and the peri-urban (Sp), which are obtained from mathematical expressions that depend exclusively on the urban area. In addition, two formulations of SUHI are considered: SUHIMAX and SUHIMEAN, which evaluate the maximum and average SUHI of the urban area for each of the three surrounding references. As the urban population growth phenomenon is a world-scale problem, this methodology has been applied to 71 urban agglomerations around the world using LST data obtained from the sea and land surface temperature radiometer (SLSTR) on board Sentinel-3A. The results show average values of SUHIMEAN of (1.8 ± 0.9) °C, (2.6 ± 1.3) °C, and (3.1 ± 1.7) °C for Su, Sf, and Sp, respectively, and an average difference between SUHIMAX and SUHIMEAN of (3.1 ± 1.1) °C. To complete the study, two additional indices have been considered: the Urban Thermal Field Variation Index (UFTVI) and the Discomfort Index (DI), which proved to be essential for understanding the SUHI phenomenon and its consequences on the quality of life of the inhabitants.

Highlights

By 2050, the world’s population is estimated to increase to nine billion, 70% of whom will live in urban areas [1]
Retrieval of land surface temperature (LST) from satellite data allows the estimation of the surface urban heat island (SUHI) as the difference between the LST obtained in the urban area and the LST of its surroundings
There is no clear definition in the literature of how to select these reference areas, and this makes it extremely difficult to compare the SUHI between different urban agglomerations

Summary

Introduction

By 2050, the world’s population is estimated to increase to nine billion, 70% of whom will live in urban areas [1]. One of the most problematic consequences of rapid urbanization is the increase of the urban heat island (UHI) [3,4], which is defined as the difference between the air temperature (AT) within the urban area and the AT of its surroundings [5]. The temperature in urban areas is higher than in rural areas, especially at night [5]. This phenomenon, which will be reinforced by the effects of climate change, affects people psychologically and physiologically, and controls daily behaviours and economic activities [6] and can lead to a drastic increase in morbidity and mortality [7], increased energy consumption [8], and even violent behaviours [9] within urban areas [10]. When the UHI is monitored with remote sensing data, we have to talk about surface urban heat island (SUHI), as the parameter studied is no longer AT, but the land surface temperature (LST) [12]

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