NEW DELHI: The national capital region has been growing warmer over the past three decades, revealed a comparative study of land surface and air temperatures as well as the heat index during the pre-monsoon season between 2015 and 2022, by the Centre for Science Environment (CSE).
The city recorded significant anomalies on all three temperature parameters. This year’s air temperature (day temperatures) has been 1.77 degrees Celsius hotter while the land surface temperature (a measure of how hot the earth’s surface is) has been 1.95 degrees C hotter than 1981-2010 baseline temperatures. The heat index (HI), which is a measure of both temperature and humidity and defines how hot one actually feels, is up by 1.64 degrees C compared to the 2010-19 baseline, the analysis report stated.
“The air temperature was the third hottest on record after 2016 and 2017, which were even hotter, registering a rise of 2.69 degrees C and 1.80 degrees C as compared to the 1981-2010 baseline temperatures. The CSE has analysed the temperature trends for India as a whole and of mega cities including – Delhi, Mumbai, Kolkata, etc from January 2015 till May 2022.
The study that aims to study the heat patterns in mega cities highlights that in Delhi the Heat Index continues to climb up despite stabilisation of air and land temperatures. “March and April have been unusually dry in Delhi but humidity started to rise in May with some scattered rain spells which brought relief from the recurring heat waves. But this spike in humidity has led to an increase in heat index in the city indicating increased thermal discomfort among the population,” it said.
The study further said that since the India Meteorological Department (IMD) doesn’t account for humidity in its consideration for heatwaves, dangers of humid heat that is known to be more lethal to humans don’t get reported. “This year the daily average heat index crossed 40 degrees C in June,” the report said. The seasonal average of the mega cities was 1-2 degrees C higher than the all-India average and 2.5-3.8 degrees C higher than northwest India.
Due to excessive hard and dark surfaces, cities tend to absorb the heat coming from the sun during the day; a city also generates a lot of waste heat due to human activities which adds to the natural heat. This extra heat should dissipate after sunset, but due to pollution and continuing generation of waste heat the city fails to cool down, leading to warmer conditions compared to rural areas, the study explained.
The highest land surface temperature (LST) in Delhi was observed in May 2020 when 53.9 degrees C was recorded within city limits. It is followed by May 14, 2022 with a maximum of 51.8 degrees C. In the previous years, maximum LST was observed to be in the mid-40s range. Besides, maximum LST is recorded from southwest Delhi around Najafgarh area followed by Badarpur and Jaitpur while minimum is recorded from near Yamuna River.
In terms of heat hotspots, Chandni Chowk recorded the highest average air temperature on May 14 this year – at 40.39 degrees C. It was followed by Punjabi Bagh at 40.29 degrees C, Mundka at 39.5 degrees C and Paharganj at 39.1degrees C. Siri Fort saw an average seasonal heat index of 38.2 degrees C.
The regions at the city periphery in the north, southwest, and northwest Delhi have seen extremely high surface temperature rise from March 19 to May 14, 2022, the analysis report said.
Delhi heat climbs up despite stabilisation of temperatures
The CSE study aims to analyse the heat patterns in mega cities
1.770 C rise in air temperature this year compared to 1981-2010 baseline
1.950 C increase in Land Surface Temperature compared to 1981-2010 baseline
1.640 C surge in Heat Index compared to 2010-19 baseline
Siri Fort and Chandni Chowk were on average hottest neighborhoods based on air temperature and heat index
The maximum land surface temperature in Delhi was recorded around Najafgarh followed by Badarpur and Jaitpur while minimum was recorded from near Yamuna River
Heat over Mega cities higher than national avg
The seasonal average of the mega cities was 1-2 degrees C higher than all-India average and 2.5-3.8 degrees C higher than north India. Due to excessive hard and dark surfaces, cities tend to absorb the heat coming from the sun during the day.