Study finds increasing tree cover can reduce experienced heat by around 1°C in Delhi neighbourhoods
Concrete expansion raises temperatures, but with a smaller impact than the cooling effect of trees
Poorer areas are hotter due to dense built-up spaces and limited access to cooling
Rising heat linked to sleep disruption, illness, loss of work and mental stress
Researchers call for neighbourhood-level heat plans and more urban greening to reduce inequality
Who feels the heat most in Delhi is shaped not just by temperature, but by trees and income, with greener neighbourhoods significantly cooler than those dominated by concrete, a new study has found.
A modest increase in tree cover can cool a neighbourhood’s experienced temperature by around 1 degrees Celsius (°C) — nearly double the warming caused by a comparable expansion of built-up concrete surfaces, according to new research by policy organisation Artha Global.
The findings, based on a survey of 2,368 households across all 70 of Delhi’s assembly constituencies combined with high-resolution satellite data, laid bare how sharply the physical shape of a city and the wealth of its residents determines who suffers most when temperatures rise.
The study, Mapping Heat Inequality Across Neighbourhoods in Delhi, found that increasing green cover from 3 per cent to 11 per cent in an area reduces the heat people actually feel by about 1°C. By contrast, expanding built-up surfaces from 25 per cent to 55 per cent raises experienced temperatures by roughly 0.6°C.
“Trees cool more than concrete heats,” the researchers said, calling urban greening “a far more powerful lever for reducing lived heat stress.”
But the implications extend well beyond discomfort.
Every 3°C rise in experienced heat triggers a cascade of effects, the study showed. Sleep disruption increases by 5 to 6 percentage points, a finding with serious long-term health implications, given that Delhi’s summer temperatures frequently swing through that range across neighbourhoods within the same city.
The poorest sleep outcomes were observed in the 42.5-47°C heat index range used in the study. Access to cooling dramatically reduces this burden, but remains uneven. Households with air conditioners spend nearly twice as much on electricity, while lower-income households often lack both appliances and the financial flexibility to increase cooling as temperatures rise.
The result is a compounding disadvantage. Poorer neighbourhoods tend to be hotter due to their built environment, and their residents are more exposed because their work and housing keep them outdoors or in poorly insulated structures for longer periods.
The report highlights that heat is fundamentally a structural issue. “Heat vulnerability is not the result of a single factor,” the researchers wrote, arguing that it arises from the interaction of microclimate, built environment and socio-economic conditions. These factors together determine how much heat people experience, how long they remain exposed, and how effectively they can buffer themselves.
At the same time, 3°C increase in temperature was also linked to a 15 percentage point rise in reported illness. In the highest heat bands, between 42.5°C and 47°C, nearly 30 per cent of individuals reported being ill for more than five days in a single month.
The data also shows clustering of chronic conditions. Heart disease, chronic obstructive pulmonary disease (COPD) and thyroid disorders peak in the 42.5-44°C range, while high blood pressure, obesity and diabetes peak between 44°C and 45.5°C.
Work is also affected. The share of households missing work due to heat rose from 18 per cent to nearly 28 per cent. And the proportion of people reporting deterioration in their mental state such as mood changes, psychological distress doubled, from 15 per cent to 30 per cent.
“Urban heat is reshaping everyday life,” the report stated, “influencing how much heat people feel, how they cope, and the toll it takes on their health and productivity.”
The researchers argue that India’s existing Heat Action Plans (HAPs), while useful, are limited by a lack of granular, context-specific data needed to protect the most vulnerable. What is needed instead, they said, are micro-level HAPs anchored at the ward level and extending down to settlement-scale “hot pockets” or the precise concentrations of heat stress.
The study also recommends establishing systems to routinely capture citizens’ lived experiences of heat, not just meteorological data, so that planning reflects how heat is actually felt and managed on the ground, rather than what satellites and weather stations record from above.
However, the report cautions that data alone will not cool cities. The physical fabric of Delhi must also change.
Given that vegetation’s cooling effect outweighs the heating impact of built-up areas, the researchers argue that tree cover should be treated as essential urban infrastructure alongside roads, drainage and power lines.
Strategically increasing green cover, the researchers argued, can offset the thermal impact of density even in the city’s most crowded neighbourhoods, and was critical to reversing Delhi’s intensifying urban heat island effect.