Delhi’s land surface temperature has nearly doubled in just over a month, worsening heatwave conditions
Delhi’s air has been blowing hot since March, but its land only started burning in late April. The heat wave season began in the capital on March 11, 2022, when the maximum ambient temperature reached 32.7 degrees Celsius, 4.5°C above normal (one of the two criteria for declaring a heat wave).
But the average temperature of the earth’s surface was only 22.6°C. On April 20, however, it rose to 45°C, even when the maximum ambient temperature was 38.4°C. The temperature on the earth’s surface has reached 62°C in and around the Bawana industrial zone in northwest Delhi.
Historically, the highest land surface temperature in the world was 70.7°C, recorded in 2005 in the Lut Desert in Iran.
This doubling of the average temperature at the surface of the ground over a short period has a major consequence as it affects municipal services and triggers the auto-ignition of fires in landfills: less than a week after the temperature at the ground surface reached 62°C in Bawana, a major fire broke out at the nearby Bhalswa landfill which burned for at least five days.
Pockets of the city with very high land surface temperatures were found to overlap its industrial areas to the north and southwest. Najafgarh, Dwarka, Naraina, Rohini, Mundka, Bawana and Narela are the main heat islands with surface temperatures exceeding 45°C.
Anand Parbat Industrial Zone and Sadar Bazaar in northeast Delhi; Badarpur and Jaitpur to the south; Shahdara, near the banks of the Yamuna River, and Kondli, in the southeast of the city, constitute the second echelon of heat islands, with ground surface temperatures ranging from 40 to 45°C.
Role of seasonal vegetation
Usually, high surface temperatures correspond to areas with low vegetation and desolate terrain. In March, plots of standing crops expanded in rural and agricultural areas in north and south-west Delhi, as well as along the bank of the Yamuna River.
The green cover kept the ground surface temperature as low as 16°C on these plots, even when the ambient air temperature soared. In April, the crops were harvested, pushing the soil surface temperature to 40°C. This seasonal denudation of land in the city seems to fuel the heat waves.
Heat island paradox
Low vegetation does not always lead to a heat island effect. The relatively greener districts of the capital such as Lutyens’ Delhi and South Delhi are exceptions. Despite higher green cover, the land surface temperature in these localities climbed to 40°C.
These places seem to have evoked a new system of heat creation that requires investigation. The indiscriminate use of air conditioners by the wealthy inhabitants of these localities leads to a significant generation of heat which is discharged into the local ecosystem. This may play a role in this paradox.
Land surface temperature in Delhi March 11, 2022 and April 20, 2022
Source: Analysis of Landsat 8 satellite imagery from the United States Geological Survey website by Sharanjeet Kaur / The Center 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 household appliances, among other factors.
Urbanization has increased significantly in Delhi’s hinterland over the past decades to support its growing population and economic activities. Delhi and the National Capital Region lost 34% vegetation cover, 12% agricultural land and 44% open/fallow land between 1990 and 2018, when built-up area expanded by 326%.
The heat island effect in the city is likely to intensify with the current rate of urbanization and landscape change. The wealthy will be able to protect themselves by using air conditioners in buildings and cars, but the poor and blue-collar workers will suffer.
Weak contingency plans
Some Indian cities such as Ahmedabad, Nagpur and Bhubaneswar have heat-related contingency plans, but they do not address the problem of urban heat islands / land surface temperature. There is a need to broaden the scope and agenda of these heat action plans.
Understanding spatio-temporal variations in surface temperature can also prove useful in addressing concerns such as climate change, thermal discomfort, and energy security.
If we continue to pour concrete on the ground and cover it with glass, while focusing all our green building efforts on increasing the energy performance of air conditioners, the temperatures on the surface of the ground will only increase. And with that, air temperatures will skyrocket, forcing the city to cook itself through the vicious circle of heat absorption.
Contributions from Avikal Somvanshi, Senior Program Manager, Urban Data Analytics Lab, CSE
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