Nights in Delhi have been getting hotter. On May 25, the city recorded its warmest night in 14 years. But this wasn’t the first time. Over the past decade, as days in the national capital have attracted more heat, its nights have stopped offering much relief, finds the ‘Making Delhi Heat-Resilient’ report by think-tank Centre for Science and Environment (CSE).
The report notes that this makes construction workers, gig workers, street vendors, the homeless, and those living in informal settlements particularly vulnerable to heat stress. Those affected include women, children and the elderly, who together comprise nearly half of Delhi’s population.
As temperatures soar, those who can afford it increasingly turn to cooling technologies, especially air-conditioners. It is no surprise then that on May 21, Delhi’s peak power demand had touched a record 8,231 MW, summing up a relentless rise in May demand over the past six years.
The growing use of ACs further aggravates the urban heat island (UHI) effect, increasing the temperature disparity between urban and surrounding areas. ACs eject heat, warming the environment for those outdoors. “Essentially, it spurs cooling inequity,” says the CSE report.
Mitashi Singh, CSE programme manager for sustainable habitat and the report’s lead author, explains that a “warm night” occurs when the maximum temperature during the day exceeds 40°C and the minimum temperature remains 4.5°C to 6.4°C above normal. On May 25, the night-time temperature reached 32.4°C, making it the warmest night recorded in 14 years.
So, why has Delhi lost its ability to cool down on summer nights? The primary reason is the increasing concretisation of the urban built environment along with shrinking green and blue spaces. Buildings are being constructed much closer together without adequate shading and insulation, while urban layouts are designed to maximise built-up space without adequately supporting ventilation.
Rajneesh Sareen, programme director for sustainable habitat at CSE, says the heat island effect makes communities that rely on outdoor work even more vulnerable because they do not have adequate means to adapt to rising temperatures. They often do not have the option of staying indoors and must continue to toil through the day to earn a living. “This becomes brutal when nights do not provide any respite. To add to this, if there is a heat-related disruption in work or if they fall sick, it results in wage losses,” says Sareen.
A May 2024 CSE report, ‘Urban Heat Stress Tracker’, had estimated that diurnal cooling in Delhi declined by 9 per cent during 2014-23. Singh explained that if the difference between day and night land surface temperatures was around 12°C during 2001-10, it had narrowed to 9.8°C by 2023.
Singh added that higher night-time temperatures could take a heavier toll on human health because the body cannot cool down after accumulating heat stress during the day. “This can lead to greater cardiovascular strain, disrupted sleep cycles and impaired tissue repair—in simple terms, lasting physiological damage,” she said.
Sareen pointed out that while heat action plans acknowledge the different vulnerable groups in Delhi, they do not offer concrete strategies to improve their resilience. “In the absence of such action, Delhi will see more and more people being affected by rising temperatures. The city needs a scientific and systematic response for its vulnerable populations,” he explained.
The CSE report recommends dual strategy to address the issue. This includes implementing year-round, city-wide measures, such as mandating thermally efficient roofs in industrial areas, office complexes, markets and informal settlements. It also recommends recognising heat as a notified disaster, developing a heat dashboard, implementing climate-appropriate urban planning, and mandating passive design principles in both new and retrofitted buildings. In addition, public cooling infrastructure needs to be developed while leveraging existing government schemes and climate funds for heat management.
For vulnerable communities, in particular, targeted interventions such as mandatory cooling breaks, staggered work timings, standard operating procedures for extreme heat events, and dedicated fiscal, medical and social support during heat emergencies should be implemented.
Heat management is no longer an occasional concern but an annual reality that is likely to persist and worsen. Sareen argued that a proactive heat management approach is needed to address rising heat vulnerability and ensure cities remain liveable in an increasingly climate-risked future.
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