Evaluation of Urban Heat Island (UHI) Using Satellite Images in Densely Populated Cities of South Asia

Manisha Maharjan,Anil Aryal,Bhesh Raj Thapa,Rocky Talchabhadel,Bijay Man Shakya,Saurav Kumar

doi:10.3390/earth2010006

Abstract

Rapid Urbanization, and other anthropogenic activities, have amplified the change in land-use transition from green space to heat emission in built-up areas globally. As a result, there has been an increase in the land surface temperature (LST) causing the Urban Heat Island (UHI) effect, particularly in large cities. The UHI effect poses a serious risk to human health and well-being, magnified in large developing cities with limited resources to cope with such issues. This study focuses on understanding the UHI effect in Kathmandu Valley (KV), Delhi, and Dhaka, three growing cities in South Asia. The UHI effect was evaluated by analyzing the UHI intensity of the city with respect to the surroundings. We found that the central urban area, of all three cities, experienced more heat zones compared to the peri-urban areas. The estimated average surface temperature ranged from 21.1 ∘C in March 2014 to 32.0 ∘C in June 2015 in KV, while Delhi and Dhaka experienced surface temperature variation from 29.7 ∘C in June 2017 to 40.2 ∘C in June 2019 and 23.6 ∘C in March 2017 to 33.2 ∘C in March 2014, respectively. Based on magnitude and variation of LST, highly built-up central KV showed heat island characteristics. In both Delhi and Dhaka, the western regions showed the UHI effect. Overall, this study finds that the UHI zones are more concentrated near the urban business centers with high population density. The results suggest that most areas in these cities have a rising LST trend and are on the verge of being UHI regions. Therefore, it is essential that further detailed assessment is conducted to understand and abate the impact of the temperature variations.

Highlights

The frequency and magnitude of extreme weather events, such as heatwaves, are expected to rise with an increase in air temperature [1]
Data was selected to maintain temporal uniformity over the study period (Table 1). This data selection should not be hindered as our study focused on land surface temperature (LST) variations and Urban Heat Island (UHI) over modified land use rather than the absolute value of LST
In the year 2015, LST was estimated for June so most of the region in Kathmandu Valley (KV) had higher temperature compared to other years

Summary

Introduction

The frequency and magnitude of extreme weather events, such as heatwaves, are expected to rise with an increase in air temperature [1] Such events are exacerbated when coupled with Urban Heat Island (UHI) effect. UHI is the phenomenon where urban air temperatures are higher than the surrounding rural areas [2]. Several factors, such as an increase in anthropogenic heat flux’s emission [3], change in urban geometry, and population density [4], and change in land-use and land cover LULC [5], results in the UHI phenomenon. Change in land cover properties alters the thermal properties, surface radiation, and humidity of the urban area [8], leading to the UHI effect. The UHI phenomenon has been widely studied [9,10,11] since its first observation by

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Conclusion