According to the study by Delhi-based climate and energy think-tank Council on Energy Environment and Water (CEEW), the 10 states and union territories with the highest heat risk include Delhi, Maharashtra, Goa, Kerala, Gujarat, Rajasthan, Tamil Nadu, Andhra Pradesh, Madhya Pradesh and Uttar Pradesh
About 57 per cent of Indian districts, home to 76 per cent of India’s total population, are currently at ‘high’ to ‘very high’ heat risk, according to a new study.
According to the study published on 20 May, Tuesday by Delhi-based climate and energy think-tank Council on Energy Environment and Water (CEEW), the 10 states and union territories with the highest heat risk include Delhi, Maharashtra, Goa, Kerala, Gujarat, Rajasthan, Tamil Nadu, Andhra Pradesh, Madhya Pradesh and Uttar Pradesh.
It also found that the number of very warm nights has increased faster than that of very hot days in the last decade.
Very warm nights and very hot days are defined as periods when minimum and maximum temperatures rise above the 95th percentile threshold, i.e., what was normal for 95 per cent of the time in the past.
The study comes as some parts of north India continue to grapple with heatwave and severe heatwave conditions. Billions of people across South Asia grapple with soaring temperatures each year, a trend scientists say has been exacerbated by human-driven climate change.
The study also flagged a rise in relative humidity across north India, including in traditionally arid regions, which worsens heat stress on the human body by slowing the process of sweating and making it harder to release heat as temperatures soar.
Factoring in more dimensions like humidity and demographics in heat risk planning, and creating a national repository of heat action plans for cross-learning between states are among the measures the study recommends to “bridge the heat resilience gap”.
India recorded more than 40,000 suspected heatstroke cases and at least 110 confirmed deaths between March 1 and June 18 last year, when its northwestern and eastern parts recorded more than twice the usual number of heatwave days.
As part of the study, CEEW researchers developed a Heat Risk Index (HRI) for 734 districts, using 40 years of climate data (1982–2022) and satellite images to study heat trends, land use, water bodies and green cover.
They also included data on population, buildings, health and socio-economic factors, along with night temperatures and humidity, for a comprehensive picture of heat risk.
“Our study found that 417 out of 734 Indian districts fell in the high and very high risk categories (151 under high risk and 266 under very high risk). A total of 201 districts fell in the moderate category, and 116 fell in either the low or very low categories.
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“This does not mean that these districts are free of heat risk, but that it is relatively lesser than that of other districts,” Vishwas Chitale, senior programme lead at CEEW, said.
According to the study, the number of very hot days is increasing in India, but concerningly, the number of very warm nights is increasing even more, creating health risks.
High night temperatures are considered dangerous because the body does not get a chance to cool down. Increasing nighttime temperature is more common in cities because of the urban heat island effect, in which the metro areas are significantly hotter than their surroundings.
“The rise in very warm nights is most noticeable in districts with a large population (over 10 lakh), which are often home to Tier-I and Tier-II cities. In the last decade, Mumbai saw 15 additional very warm nights per summer, Bengaluru (11), Bhopal and Jaipur (7 each), Delhi (6) and Chennai (4),” the report said.
The study revealed that even in the traditionally cooler Himalayan regions, where heat thresholds are lower than in the plains and coasts, both very hot days and very warm nights have increased.
This could severely impact the fragile mountain ecosystems.
For example, in the union territories of Jammu and Kashmir and Ladakh, the number of very hot days and very warm nights rose by over 15 days and nights each summer.
The study also showed that north India’s summer humidity climbed from 30-40 per cent to 40-50 per cent in the last decade, worsening heat stress, especially in the Indo-Gangetic plain where farm workers toil outdoors.
Also, early mornings now feel hotter due to humid conditions. Cities like Delhi, Chandigarh, Jaipur and Lucknow have seen a 6–9 per cent rise.