From disrupting sleep and threatening pregnancies to hitting livelihoods, heatwaves fall hardest on the urban poor, with experts across disciplines converging on a common response -- that passive cooling, built into roofs, walls, and public spaces, is a public health intervention that can no longer be overlooked. Identifying what passive cooling solutions are in practice, Benjamin Hickman, Programme Manager at the United Nations Environment Programme (UNEP) in India, noted that while cool roofs can reflect heat away from low-income communities, they work best when combined with other relatively affordable measures such as roof insulation, appropriate building materials, traditional practices, and shading of windows, walls, and roofs.
Hickman, who has spent 12 years leading initiatives on sustainable cooling, highlighted that a critically overlooked aspect is extracting heat from buildings, especially at night through exhaust and forced ventilation, while keeping windows shut during the day.
"But those strategies need to be adapted according to climate zones. While insulation and shading must be prioritised in hot, dry areas, ventilation, including exhaust fans, and shading are most effective in the humid ones," the UNEP official told PTI.
Citing their cool-roof project at New Delhi's Kashmere Gate bus terminal, he underscored the importance of passive cooling in outdoor spaces such as footpaths, bus stops, and cycling infrastructure -- all of which draw high footfall from vulnerable populations -- including nature-based solutions.
He further said that for highly exposed workers in factories or construction sites, solutions include cooling vests, well-shaded rest areas, shifted working hours, and parametric insurance for heat-forced work stoppages.
"Low-income areas are also disproportionately hit by heatwave-triggered power outages, driven by peak cooling demand, yet these communities contribute least to that demand. An air conditioner uses up to 30 times more power than a ceiling fan," Hickman told PTI.
"If we narrow the lens to extreme heat specifically, passive cooling is a major public health tool that can protect people during heat waves, and we know it works," he added.
The UNEP has been working with central and state governments to integrate passive cooling into heat action plans, building regulations, schools and affordable housing schemes, measures that can reduce hours of discomfort by up to 35 per cent while remaining affordable, according to the UN body. The activities are supported by the Government of Switzerland.
Explaining the impacts of extreme heat on vulnerable populations, Dr Harshal Salve, a physician at the All India Institute of Medical Sciences (AIIMS), classified them into two categories: short-term acute impacts, ranging from convulsions and confusion to heat stroke, and long-term impacts gradually leading to hypertension and cardiovascular morbidities.
"In pregnant women, heat exposure affects outcomes for both mother and newborn, in the form of low birth weight, premature delivery, and congenital malformations," Salve -- whose ICMR-supported research is assessing heat's impact on occupational settings in Delhi-NCR -- told PTI.
He said impacts are further aggravated in those with pre-existing conditions such as cardiovascular disease, diabetes, and hypertension, and can be reduced through passive cooling interventions at the household level.
Salve further said that while children under five and adults over sixty are at greater risk, the threat is compounded further for those above 65, roughly one in three of whom already live with chronic conditions.
"Studies have also found that residents of uppermost floors of high-rise buildings are more vulnerable to heat, regardless of their economic status. Passive cooling solutions are therefore more feasible and practical for addressing the problem," the doctor said. Pointing to passive cooling's potential, Siraz Hirani, Director at Mahila Housing Trust, said cooling stations built entirely on passive technologies in Jodhpur, Jaipur, and Churu in Rajasthan are delivering temperatures 10 to 12 degrees Celsius lower than outside, with zero electricity.
"These solutions matter because most people spend their days outside, in transit, markets, or worksites, where air conditioning simply isn't an option. Making public spaces thermally comfortable through passive cooling addresses a gap that active cooling never can," Hirani told PTI.
The Mahila Housing Trust Director emphasised that scaling solutions through active cooling alone is neither feasible, affordable, nor environmentally sustainable, and with rising temperatures across the country, passive cooling is "not merely about comfort but is a critical health imperative".
Speaking about the challenges of implementing such measures on the ground, Hirani told PTI that even when passive cooling practices are acknowledged in policy, local enforcement remains weak.
"The government has taken progressive steps to actively encourage these passive cooling and climate-resilient designs, notably various incentives. However, the real challenge lies in ensuring these measures are effectively integrated at the implementation stage. Even when passive cooling practices are acknowledged in policy, local enforcement is weak," he said.
When asked whether passive cooling interventions translate into measurable health outcomes, Ritika Kapoor, Climate and Health specialist at NRDC India, said cool roof pilot projects consistently recorded a temperature reduction indoors, with follow-up surveys showing residents felt more comfortable, spent more time inside during peak hours, and reported better sleep.
"This last point is particularly important -- vulnerability to heat stress is not limited to heat stroke. It also increases when people haven't slept well or when the body hasn't had adequate time to recover overnight," she told PTI.
Kapoor argued that while early warning systems, hydration advisories, and hospital readiness remain important, they address the crisis once it has already struck. Passive cooling, she said, shifts the focus upstream -- and much like safe water and sanitation, should be treated as preventive public health infrastructure.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)