India's capital, Delhi, has been grappling with a severe heatwave for several weeks, with daily air temperatures consistently exceeding 40C. However, a recent investigation using thermal imaging has revealed a stark difference between official air temperature readings and the actual heat experienced on the city's streets, with significant implications for public health.
On a day when the Indian Meteorological Department (IMD) reported a maximum air temperature of 43.5C, a thermal camera deployed by Greenpeace India recorded surface temperatures reaching an astonishing 64C in certain locations. This substantial disparity is due to the nature of measurement: IMD data reflects air temperature under standard conditions, while thermal cameras measure the heat radiating from surfaces. Hard surfaces like roads, concrete, and vehicles absorb and re-emit heat, becoming considerably hotter than the surrounding air.
The impact of this surface heat was dramatically illustrated at the IIT flyover in south Delhi, a major traffic hub. Greenpeace researcher Nibedita Saha observed that while shaded areas under the flyover registered 42C, the surface temperature where bikers idled at traffic signals in direct sunlight soared to 64C. Even a move of less than ten feet to stand under a tree brought the surface temperature down to 39.8C, demonstrating the immediate relief shade can provide.
Dr A Fathahudeen, a pulmonologist, emphasised the serious health risks posed by prolonged exposure to such high temperatures. He explained that the human body's core temperature is 37C, and when it exceeds 40C, normal bodily functions begin to fail. Common symptoms include heat exhaustion, headaches, and fatigue, escalating to confusion, seizures, and potentially multiple organ failures and death if not treated promptly. Dr Fathahudeen advises staying hydrated, wearing loose, light-coloured clothing, and using an umbrella to mitigate risks.
The challenges are particularly acute for Delhi's working poor, who often have no option but to remain outdoors. Street vendors, such as Sanjana Ben, who sells dry fruits near the Red Fort, reported feeling the relentless heat from both the sun and the scorching ground. Her face registered around 40C with the thermal camera, but the ground inches away from her reached 57C. These findings underscore the urgent need for measures to protect vulnerable populations from the escalating dangers of urban heat.