Subscribe
Delhi’s air has been blowing hot since March but its land started to scorch only by late April. Heatwave season began in the capital on March 11, 2022, when the maximum ambient temperature hit 32.7 degrees Celsius — 4.5°C higher than normal (one of the two criteria for declaring heatwave).
But the average land surface temperature was only 22.6°C. On April 20, however, it rose to 45°C, even when the maximum ambient temperature was 38.4°C. Land surface temperature hit 62°C in and around the Bawana Industrial Area in northwest Delhi.
Historically, the highest land surface temperature in the world was 70.7°C, recorded in 2005 in the Lut Desert of Iran.
This doubling of average land surface temperature over a short span is of major consequence as it affects city services and triggers auto-ignition of fires at landfills: Less than a week after land surface temperature reached 62°C in Bawana, a major fire broke out at the neighbouring Bhalswa landfill that burnt for at least five days.
Pockets of the city with very high land surface temperatures were found to overlap with its industrial zones in the north and southwest. Najafgarh, Dwarka, Naraina, Rohini, Mundka, Bawana and Narela are the prominent heat islands with land surface temperatures exceeding 45°C.
Anand Parbat Industrial Area and Sadar Bazaar in northeast Delhi; Badarpur and Jaitpur in the south; Shahdara near the banks of Yamuna river and Kondli in the city’s southeast are the second-rung of heat islands, with land surface temperatures ranging from 40-45°C.
Usually, high surface temperatures correspond to areas with low vegetation and desolate terrain. In March, patches of standing crop stretched across rural and agricultural areas in north and southwest Delhi, as well as along the Yamuna river bank.
The green cover kept the land surface temperature as low as 16°C over these land parcels, even as the ambient air temperature soared. In April, the crops were harvested, pushing the land surface temperature to 40°C. This seasonal denuding of land in the city seems to be fueling the heatwaves.
Low vegetation doesn’t always lead to a heat-island effect. Relatively greener neighborhoods of the capital such as Lutyens’ Delhi and South Delhi are exceptions. Despite a higher green cover, land surface temperature in these localities climbed to 40°C.
These places seem to have conjured up some novel heat-creating system that needs investigation. Indiscriminate use of air conditioners by the rich denizens of these localities leads to significant heat generation that is dumped in the local ecosystem. This may play a part in this paradox.
Land surface temperature in Delhi on March 11, 2022 and April 20, 2022
Source: Analysis of Landsat 8 satellite imagery from United States Geological Survey website by Sharanjeet Kaur / The Centre for Science and Environment (CSE)
Urban heat islands are hotspots where temperatures are higher than average due to concrete structures as well as emissions from automobiles and domestic appliances, among other factors.
Urbanisation has increased significantly in Delhi’s hinterlands over the past few decades to support its increasing population and economic activities. Delhi and the National Capital Region lost 34 per cent of its vegetation cover, 12 per cent agricultural land and 44 per cent open / fallow land during 1990-2018, when the built-up area expanded by 326 per cent.
Heat-island effect in the city is likely to further intensify with the current rate of urbanisation and landscape modification. The rich people will be able to shield themselves using air conditioners in buildings and cars, but the poor and blue-collared workers will suffer.
Some Indian cities such as Ahmedabad, Nagpur, and Bhubaneswar have heat emergency plans but they don’t address the problem of urban heat islands / land surface temperature. There is a need to expand the scope and agenda of these heat action plans.
Understanding the spatial-temporal variations of surface temperature can also prove to be useful in addressing concerns such as climate change, thermal discomfort and energy security.
If we continue to pour concrete on the ground and clad it with glass, while concentrating all our green building efforts in just ratcheting up energy performance of ACs, land surface temperatures will only increase. And with that, air temperatures will soar, making city cook itself through vicious cycle of heat absorption.
Inputs by Avikal Somvanshi, Senior Programme Manager, Urban Lab, CSE