As Delhi endures weeks of severe summer heat, with official air temperatures routinely surpassing 40C, thermal imaging and household monitoring are revealing a more extreme reality on the ground — where sun-baked roads, concrete structures, and poorly ventilated homes push temperatures well beyond what official weather stations record.
On a recent day, the Indian Meteorological Department recorded a maximum air temperature of 43.5C in the capital. But a thermal camera deployed by Greenpeace India captured surface temperatures of up to 64C at a busy traffic junction in south Delhi, highlighting the gap between standard air measurements and the actual heat experienced by people in urban environments.
The difference stems from how temperatures are measured. Official data reflects the temperature of the air under standard conditions, while thermal cameras record the temperature of surfaces. On hot days, roads, concrete, vehicles, and other exposed surfaces can become substantially hotter than the surrounding air. High surface temperatures increase the heat absorbed by the human body through radiation, making urban areas feel considerably hotter than the official reading — particularly where there is little shade or vegetation.
At the IIT flyover in south Delhi, one of the city's busiest traffic junctions, Greenpeace researcher Nibedita Saha measured surface temperatures of 64C on bikers waiting at stop signals under direct sunlight. The spot where she stood recorded 61C, but moving less than 10 feet to stand under a tree dropped the reading to 39.8C. Areas shaded by the flyover registered 42C.
"Consistent exposure to such high temperatures can cause major health issues," says Nibedita, adding that sometimes moving just a few feet can help. "We got instant relief under the tree," she observed.
The heat is not confined to the streets. In the cramped lanes of Delhi's Sundar Nagri district, a densely packed area home to some of the city's poorest residents, families describe homes that offer little refuge from the heat.
Durga Devi, a 45-year-old factory worker, spends eight hours a day working without a fan, then returns at dusk to a stifling one-room house. The structure — with concrete walls, low roofs, and poor ventilation — traps heat during the day and stays oppressively hot through the night. Devi says she has recorded temperatures as high as 45C on her bedroom wall at night, while the concrete road outside registered 60C during the day.
"I prefer staying outside after work, because inside the house there is no relief," she said.
Her son Abhishek, a 21-year-old student, has been keeping a heat diary as part of a Greenpeace India initiative that involves 20 families in the area. Using a thermal camera, he tracks temperatures inside the home and around the neighbourhood to document living conditions.
"I want to show how high the temperature goes here, and what it is like to live in this condition," Abhishek said. His findings show temperatures well above those recorded by official meteorological stations.
"Heat doesn't end when the temperature outside falls," said Deepali Tonk, who has helped organise the project for Greenpeace India. "For many families, the structure of their homes and the materials they are built from mean there is no place to recover."
The campaign aims to push policymakers to better protect vulnerable communities, highlighting how urban design and housing quality can amplify the effects of extreme heat. Researchers estimate that extreme heat is responsible for thousands of excess deaths nationally each year, though the exact figure remains a matter of ongoing study.
As climate change drives more frequent and intense heatwaves, the gap between official temperatures and the lived experience of residents in poorly shaded, poorly ventilated urban areas is becoming a critical concern — and one that thermal imaging is now bringing into sharper focus.