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Delhi's air, surface temperatures above baseline avg, study finds

Published on Jul 08, 2022 02:33 AM IST

The highest surface temperature this year was 51.8°C on May 14 at outer Delhi’s Narela, Bawana, Fatehpur Jat and south-east Delhi’s Badarpur.

Delhi's air, surface temperatures above baseline avg, study finds. (HT Photo)

Air and surface temperatures in Delhi between March and May this year were significantly higher than the 1981-2010 baseline, and the heat index was well above a more recent 2010-19 threshold, found a study by the Centre for Science and Environment (CSE).

The study, ‘‘Urban Heat Stress in major cities of India: Delhi” found that the Capital’s average air temperature from March to May (considered the pre-monsoon period) this year was 30.03°C, higher than the 30-year baseline (1981-2010) of 28.25°C, while the average land surface temperature was 1.95°C than its baseline. At the same time, Delhi’s heat index (also known as the ‘real feel’ of the weather) was 30.53°C, higher than the baseline figure of 28.89°C.

The highest surface temperature this year was 51.8°C on May 14 at outer Delhi’s Narela, Bawana, Fatehpur Jat and south-east Delhi’s Badarpur.

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It also found that surface temperatures in some parts of the city hit a high of 53.9°C in the past eight years.

The CSE analysis used the United States Geological Survey’s (USGS) EarthExplorer portal to analyse land imagery and thermal infrared sensor data, assessing change in heat patterns for Delhi over the years during the pre-monsoon season.

For land surface temperature (LST) satellite maps, readings from 2014, 2016, 2018, 2020 and 2022 were also checked, with the figure peaking on May 16, 2020, at 53.9°C in Badarpur and Narela.

Almost all of Delhi this year logged peak land surface temperatures above 42°C, the study said.

The data bolsters regular temperature readings for the summer months this year, which have been well above normal for much of March, April, May and early June (which was not part of the CSE study). A string of heatwaves oppressed the city between March and May, with temperatures well above normal and a persistent dry spell compounding the general sense of discomfort. Even as temperatures dipped in the latter half of June, rising humidity levels kept the heat index at record levels.

“The maximum LST was recorded in the south-west part of the city, in areas around Najafgarh, during the time period examined in this study. Apart from Najafgarh, Badarpur and Jaitpur are other neighbourhoods that show consistently high LST with levels above 40°C,” said the study, adding that in May, the surface mercury across Delhi shot above 38°C even in the city’s green pockets.

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It added that, in general, the areas with the lowest LST were those along the Yamuna and near the Okhla Bird Sanctuary.

The study also finds a considerable difference the heat index and air temperature across the city during the pre-monsoon period this year, finding the gap to be as wide as six degrees between neighbourhoods.

Chandni Chowk recorded the highest seasonal air temperature, with an average reading of 34.2°C, Aurobindo Marg at 28.1°C was the city’s coolest spot.

From a heat index perspective, Siri Fort recorded the highest seasonal average at 38.2°C, followed by Chandni Chowk at 36.8°C. Shadipur (29.1°C) and Aurobindo Marg (29.6°C) were on the other end of the spectrum, recording the lowest average seasonal heat index reading.

“Understanding the overall temperature anomaly, extreme heat conditions, and the mixed trends in heat patterns across different regions of India has become necessary to assess the emergent risk. Currently, the attention is largely on the maximum daily heat levels and extreme conditions of heat waves, but it is equally important to pay attention to the overall rising temperature and humidity trends in different regions to understand the gravity of the problem,” says Avikal Somvanshi, senior programme manager at the Urban Lab of CSE and also the co-author of the study.

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Anumita Roychowdhury, executive director, research and advocacy, CSE says without heat-action plans and the erosion of heat-dousing forests, urban greens and water bodies, health risks related to heat stress will only increase. “Policy preparedness to mitigate rising heat due to climate crisis is nearly absent in India and this trend shows the need to act against urban heat stress by reversing concretisation, heat-trapping structures and waste heat from industrial processes and air conditioners,” she says.

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