- A white paper on heat in India says historical temperature records in northern India may understate future heat risk.
- The paper examines heat action plans, cool roofs and parametric insurance as important but limited responses to heat that affects work, housing, health and public finance.
- The paper says about three-fourths of India’s workforce is engaged in heat-exposed labour.
“A construction worker in Ahmedabad who labours through 45-degree heat loses income, risks injury, returns to a poorly ventilated home that doesn’t cool down at night, and has no social protection to fall back on. That’s a labour problem, a housing problem, a health problem, and a finance problem, all at once, in a single day,” said Kartikeya Bhatotia, co-author of the finance chapter of a new Harvard University white paper on extreme heat in India. Bhatotia used the example of a day in Ahmedabad, when above-normal temperatures this year almost touched 45°C, to explain why heat in India cannot be treated only as a weather event.
In fact India may be significantly underestimating its future heat risk, according to a white paper, Critical Perspectives on Extreme Heat in India, released in April 2026 and supported by Harvard University’s Salata Institute for Climate and Sustainability. The paper, which examines how heat reshapes life and livelihoods in India, draws from discussions from the India 2047: Building a Climate-Resilient Future workshop in New Delhi held in March 2025. Bhatotia was one of the organisers of this workshop.
The white paper says extreme heat is “the deadliest climate hazard globally” but remains among the least resourced in adaptation planning. It estimates that about three-fourths of the country’s workforce, roughly 380 million people, is engaged in heat-exposed labour, while the capacity to adapt remains unequal.
The white paper argues that heat cannot be understood through a single threshold or impact. A short, intense heatwave threatens the elderly; sustained months-long heat erodes outdoor workers’ productivity; over longer periods, it damages infrastructure. “The biggest gap is that we are still treating heat as an episodic disaster rather than a structural, economy-wide risk,” Bhatotia said.
“Most current responses are designed for short-term relief. They help people get through a heatwave, and they have varying efficacy on varying metrics: cool roofs reduce indoor temperatures by a few degrees in some settings, heat action plans can reduce mortality when activated during discrete events, and parametric insurance provides income protection during payout windows,” explains Bhatotia. “Each of these has value, but would contribute incrementally towards climate adaptation.”
Planning for a hotter future
The paper notes that historical temperature records, particularly in northern India, are not an accurate baseline for planning.
Data shows that monthly maximum temperatures in India have been rising since 1980, by about 0.28°C per decade. In the 2015-2024 period, the average temperature is 0.88°C hotter relative to the 1980–1990 period, as noted in the paper by Peter Huybers, department chair and professor of Earth and Planetary Sciences and Environmental Science and Engineering.
However, India’s average temperature rise has been somewhat muted, compared to global land warming, says Bhatotia, a Harvard climate fellow. The reasons for the muted the temperature rise, though, may not last and could change. Thus, understanding this warming gap is important for adaptation planning.
When examining the muted temperature rise, the paper notes that some cooling, or suppression of temperatures, particularly in northern India, has been because of aerosols and irrigation. “Aerosols, particularly in the Northern Indian plains, from crop-residue burning, industry, and traffic, scatter incoming sunlight and cool daytime surface temperatures. Irrigation cools near-surface air, typically measured about two metres above ground, by promoting evapotranspiration,” he said. But these cooling mechanisms may change or weaken in the coming decades. So, local trends, do not show the complete picture and cannot be relied on for adaptation planning.
The warming deficit — or the gap where the temperature increase is smaller than it should be — is likely the result of “multiple overlapping factors,” with their relative contributions still being researched, says Bhatotia.
“The recent historical temperature record in northern India likely understates the warming that the coming decades will bring,” he said. “Heat action plans, and any other instruments of climate adaptation calibrated to historical averages risk systematic underestimation of the exposures populations will face within those instruments’ own planning horizons. A warming trend that has appeared modest over recent decades may not remain so.”
Looking beyond cool roofs
The white paper’s built-environment chapter says cool roofs are important as a strategy for managing heat in buildings, but not sufficient.
Rajan Rawal and Radhika Khosla, experts on the built environment, write that a focus on roofs alone can create a false sense that overheating problems have been solved. They argue for a wider approach that includes passive design strategies addressing conduction, convection and radiation through building materials, construction techniques and spatial configuration.
Rawal, professor at CEPT University and senior advisor at the Centre for Advanced Research in Building Science and Energy (CARBSE), said heat enters buildings through multiple surfaces. “Heat ingress in buildings is from walls, windows, and the roof. Warm/hot air enters buildings through open windows, and solar radiation also penetrates through them. The wall also transmits the heat through the material. The floor also absorbs heat from the warm soil beneath it.”
The relative importance of each surface depends on the building. “In multi-storey structures, the combined surface area of the walls and windows is significantly larger than that of the roof. Consequently, the roof may only represent approximately 5% of the total exterior surface area, making vertical surfaces the dominant contributors to heat ingress in multi-storey buildings,” he said.
Rawal said design and construction measures such as shading, operable ventilators, specialised glass and low-conductivity wall materials can reduce heat ingress. But passive design may not be enough on its own across India’s diverse climatic zones. “A more robust approach involves a hybrid model, where passive design is integrated with low-energy cooling systems,” he said.
He also cautioned against over-reliance on land surface temperature data in urban planning. “Current policies rely disproportionately on land surface temperature data, leading to a reductive and often erroneous focus on surface treatments alone. By doing so, these frameworks marginalise the vital roles of ambient air temperature and relative humidity. This narrow focus ignores the complex meteorological interplay essential for human thermal survival, potentially rendering urban interventions ineffective.”
Insurance, labour, health and fiscal risk
The paper, in its chapter on insurance, notes a specific limitation of the new adaptation tool of parametric heat insurance, which is intended to compensate workers with a cash payout on extremely hot days to compensate for lost wages. It notes that workers who buy parametric products are unlikely to stop working on hot days because they cannot predict whether payout conditions will be met on a given day. The payout may therefore compensate workers after exposure, rather than protect them from heat-related health risks, as is the intent.
Informal workers constitute as much as 90% of India’s workforce. Formal employer-based protections, hence, do not apply to them. Heat is then not only a health risk for these workers but also an economic burden because avoiding exposure means lost wages, while falling ill means medical spending.
“When the state underinvests in heat resilience, and employers externalise costs to workers, those costs don’t disappear; they are shifted downward,” says Bhatotia. “They show up as lost wages on dangerously hot days, higher out-of-pocket spending on cooling and health, and reduced ability to absorb shocks.”
India still struggles to measure the true health burden of heat, says the paper in its health chapter. Many heat-related illnesses and deaths go unrecorded or are misclassified, private-sector health data remain largely absent from national registries, and meteorological and health data are fragmented.
This data gap affects adaptation planning, says Bhatotia.
“In a very literal sense, India cannot fully see the health and economic burden of heat. Private providers, who account for the majority of inpatient care, are largely missing from national datasets. We are working with outdated population baselines due to our delayed census. Even meteorological data is not always a public good. The result is that we are trying to plan for a systemic risk with partial visibility, which inevitably leads to underestimation,” he says.
Warm nights and city risk
Vishwas Chitale of the Council on Energy, Environment and Water, who is not part of the report, pointed to another dimension of heat risk in India.
“As per CEEW’s analysis, nearly 57% of Indian districts, home to about three-fourths of the population, are already at high to very high heat risk. Beyond rising daytime temperatures, a critical concern is the sharp increase in warm nights — over 70% of districts have seen at least five additional warm nights annually in the last decade (2012–2022) compared to the 1982–2011 baseline,” Chitale said.
He said the rise in warm nights changes how cities need to understand and respond to extreme heat because preparedness has traditionally focused on peak daytime temperatures. “When nights remain warm, the human body does not get the chance to recover from accumulated daytime heat stress. This leads to cumulative exposure, increasing the risk of heat exhaustion and heatstroke, especially for vulnerable groups such as the elderly, those with pre-existing conditions, and people living in poorly ventilated homes,” he said.
For cities, Chitale said, this means moving from a “daytime-only” response to a “24-hour heat management approach.” Early warning systems need to account for night-time temperatures and “feels-like” conditions, not just daytime peaks, while cooling strategies must prioritise indoor thermal comfort through cool roofs, better ventilation and access to affordable cooling, he said.
“It also calls for rethinking work-rest cycles, strengthening night-time healthcare readiness, and ensuring that the most vulnerable populations have access to safe, cooler environments even after sunset. In simple terms, warm nights turn heatwaves from short-term events into prolonged stress periods, and preparedness must evolve accordingly,” he said.
Read more: Humid heat rises on the coasts of India impacting health
Banner image: Labourers sleep on a road median in Lucknow, Uttar Pradesh in the summer of 2024. Beyond rising daytime temperatures, a critical concern for experts is the sharp increase in warm nights. (AP Photo/Rajesh Kumar Singh)
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