More than Half of India's Districts Vulnerable to 'High to Very high' Heat Risk: Study

The Wire

6 hours ago

More than half of India's districts are vulnerable to 'high to very high' heat risk, according to a recent study by Delhi-based think tank Council on Energy, Environment and Water.
The top 10 states and union territories that are threatened by the highest heat risk are Delhi, Maharashtra, Goa, Kerala, Gujarat, Rajasthan, Tamil Nadu, Andhra Pradesh, Madhya Pradesh and Uttar Pradesh.
The study recommends that Heat Action Plans – which are currently used at the district level to prepare for heat hazards and exposure – be updated regularly, and that it take into account aspects such as the rise in warmer nights and relative humidity which the study noted as new trends over the past decade.
India has been experiencing record-breaking heat in recent times.
For instance, the India Meteorological Department (IMD) announced that February 2025 was the hottest that India has witnessed in 125 years. Last year, in a first, Mungeshpur in northwest Delhi clocked 52.3° Celsius in May (which authorities put down as an 'outlier' possibly due to 'sensor errors').
Per the IMD, a heatwave is said to occur over a region if the maximum temperature goes above 45°C, or when temperatures increase from between 4.5°C and 6.4°C above the normal; and a severe heatwave is said to occur when maximum temperatures exceed 47°C, or rises above normal levels by 6.4°C and higher. Both are known to impact people – their health and livelihoods – in several ways. Some sections of people are more prone to these heat hazards than others. According to the United Nations' Intergovernmental Panel on Climate Change (IPCC), heat risk is a combination of heat hazard, exposure and vulnerability.
A team of scientists at the Council on Energy, Environment and Water (CEEW), Delhi, developed a heat risk index (HRI) for 734 districts in India to assess heat risk at district-level across the country. They mapped long-term heat trends from 1982 to 2022 using both satellite imagery and the Indian Monsoon Data Analysis and Assimilation, which is a high-resolution climate dataset. The team also included several other variables in their analyses, such as socio-economic and health factors, land-use, population and green cover while also looking at trends in night-time temperatures and relative humidity levels.
The Heat Risk Index in the report of the Council on Energy, Environment and Water.
on May 20, showed that 57% (417) of India's 734 districts – which are home to more than three-quarters of the country's total population – are currently at high to very high heat risk. Specifically, 151 districts fell under the 'high risk' category and 266 under the 'very high risk' category. While 201 districts fell in the moderate category and 116 fell either in the low or very low categories, this does not mean that these districts are free of heat risk, but instead that heat risk in these districts is relatively lesser when compared to others, according to the study.
The team aggregated these risks at the state level and found that the ten states and union territories with the highest heat risk are Delhi, Maharashtra, Goa, Kerala, Gujarat, Rajasthan, Tamil Nadu, Andhra Pradesh, Madhya Pradesh and Uttar Pradesh.
They also found that while the number of very hot days is increasing in India, the number of very warm nights is increasing at an even greater rate. Over the last decade, nearly 70% of India's districts experienced an additional five very warm nights per summer (March to June). In comparison, only ~28% of districts experienced five or more additional very hot days.
This is a concern because usually, when daytime temperatures increase, nights cool down providing much-needed relief to people. However, when nights get warmer, the human body finds it harder to cope with the increased daytime temperatures and unusually warmer nights.
Cities and the urban heat island phenomenon
The team found that the urban heat island effect – where increased urbanisation and the resulting concretisation keeps temperatures in built-up areas far higher than it would have been if it had green cover – also plays a role in this trend in the increase in very warm nights.
Their data showed that 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 II cities. Per the study, just over the last decade alone, several metros witnessed an additional number of very warm nights per summer: Mumbai witnessed 15, Bengaluru 11, Bhopal and Jaipur witnessed seven each, Delhi experienced six additional very warm nights, as did Chennai (4).
'This increase can be attributed to the urban heat island effect, where cities trap heat during the day and release it at night, thus increasing nighttime temperatures. With nearly 50 per cent of India's population expected to live in urban areas by 2050, this poses a serious threat to the population (UN-DESA 2018),' the study noted.
It also found that districts with increased heat extremes but lower vulnerability – such as in Odisha – had higher green cover and better blue infrastructure: 'factors enhance adaptive capacity, helping communities cope more effectively with extreme heat'.
Increases in relative humidity is yet another concern. Per the study, the Indo-Gangetic plain experienced the highest summer relative humidity increase in the last decade. 'Cities like Delhi, Chandigarh, Jaipur, and Lucknow are also experiencing a 6 to 9 per cent rise in relative humidity,' the CEEW study noted.
'Danger doesn't end when the sun sets'
According to the study, the phenomena of increased warm nights and relative humidity need to be factored into existing Heat Action Plans, which are documents that outline strategies and measures to prepare for, respond to and mitigate the impacts of extreme heat events.
India must invest in 'long-term resilience', commented Vishwas Chitale, Senior Programme Lead at CEEW, and a co-author of the study. 'Solutions like parametric heat insurance, early warning systems, net-zero cooling shelters, and cool roofs must become core to heat action plans. States like Maharashtra, Odisha, Gujarat and Tamil Nadu are already taking pioneering steps by integrating climate and health data into local planning. Now is the time to scale these efforts nationally, using district-level risk assessments to prioritise funding and action,' Chitale said in a statement.
'Heat stress is no longer a future threat – it's a present reality,' Arunabha Ghosh, CEO of CEEW, said in a press statement. 'Increasingly erratic weather due to climate change – record heat in some regions, unexpected rain in others - is disrupting how we understand summer in India. But the science from the study is unequivocal: we are entering an era of intense, prolonged heat, rising humidity, and dangerously warm nights.'
He added that city-level Heat Action Plans must be 'urgently overhauled' to address local vulnerabilities, balance emergency response measures with long-term resilience, and secure financing for sustainable cooling solutions.
'Further, it's time to move beyond daytime temperature thresholds and act on what the data tells us: the danger doesn't end when the sun sets.'