Land surface temperature increases by 5 degrees over 20 years in SoBo

Published on Aug 05, 2022 07:33 PM IST
With the world’s temperature increasing continuously for the last 150 years, the densely-populated coastal city of Mumbai has not been spared
For this study, titled ‘Impact of Land-Use Dynamics on Land Surface Temperature in Mumbai City’, researchers used remote sensing data from NASA’s Landsat Program to assess changing land use in Mumbai city (Satish Bate/HT PHOTO)
For this study, titled ‘Impact of Land-Use Dynamics on Land Surface Temperature in Mumbai City’, researchers used remote sensing data from NASA’s Landsat Program to assess changing land use in Mumbai city (Satish Bate/HT PHOTO)
ByPrayag Arora-Desai

Mumbai With the world’s temperature increasing continuously for the last 150 years, the densely-populated coastal city of Mumbai has not been spared.

Land surface temperature (LST) in south Mumbai became warmer by 5 degrees Celsius (°C) between 2000 and 2020, according to a new study led by researchers at the National Environmental Engineering Institute (NEERI). The study found that the average LST of the city increased from 27.1°C to 32.2°C over 20 years, which experts said is a direct result of an increase in built-up area and a decrease in vegetation and water bodies, leading to an exacerbation of the urban heat island (UHI) effect.

For this study, titled ‘Impact of Land-Use Dynamics on Land Surface Temperature in Mumbai City’, researchers used remote sensing data from NASA’s Landsat Program to assess changing land use in Mumbai city and its impact on heat. They analysed monthly temperature data for the years 2000, 2010, 2015, and 2020, and the average annual LST was found to be 27.1°C in 2000, 27.8°C in 2010, 31.8°C in 2015, and 32.2ºC in 2020. The main urban heat pockets in South Mumbai were identified as CST, Mumbai Port Trust facility, and slum clusters in Sion and Dharavi.

Land Surface Temperature (LST) is a measure of how hot the surface of the earth is at a particular location, and is measured remotely by satellite through infrared sensing. It is a measure of surface temperature, and differs from ambient temperature, which is a measure of heat in the air or atmosphere, and is used to express weather conditions in meteorology. However, LST and ambient temperature are positively correlated.

In Mumbai city, increasing LSTs have resulted in a warmer atmosphere as well, with average daily temperature rising by 1.9 degrees from around 36 degrees in 2000 to just under 38 degrees in 2020.

“There are significant changes in the lower and upper range of LST from 2000 to 2020 and the area coverage by the highest temperature zone is increasing, which is shown in the spreading of thermal discomfort zones in the city. It is observed that the high density of built-up area along transportation networks (roads, railways) is more responsible for the increase of LST in central Mumbai. The presence of vegetation in the central part and western portions of the city makes it cooler when compared with highly urbanised places like Malabar hill, Tardeo, Worli, Colaba,” the study notes.

F/N Ward, which includes Matunga and surrounding areas, were found to have the highest LST in 2020, at 34 degrees Celsius. D Ward, including Grant Road and surrounding areas, was found to have the lowest LST in 2020, at 31.8 degrees Celsius. However, all nine wards in Mumbai city recorded an increase.

The NEERI study affirms another paper (led by the Faculty of Natural Sciences at Delhi’s Jamia Millia Islamia University), published last year in the peer-reviewed Springer Journal of the Indian Society of Remote Sensing, which found that Mumbai lost 58.17% of its open spaces, 40% of its green cover and about 25.30% of water bodies between 1991 and 2018.

These transformations were found to radically alter land surface temperature dynamics, leading to more intense urban heat island formation.

“We observed that the average temperature in 1991 was 34.08 degrees Celsius. It rose to 36.28 degree Celsius in 2018 (a 2.2-degree Celsius increase) under the heat island zones (vulnerable areas), thus exposing people to higher heat risk,” said Shahfahad, one of the researchers.

Roshni Udyavar Yehuda, president, Institute of Environmental Architecture and Research, who was not involved with the study, said that the UHI effect is caused due to an increase in hardscapes such as building materials including concrete, steel and glass, both on the buildings and on streetscapes or open spaces.

“Curtailment of wind flow which often occurs in urban areas due to closely built vertical structures is also a problem,” she explained, emphasising that such micro-climatic changes must be clearly reflected (and prepared for) in Mumbai’s official development plan.

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