Rising heat risks threaten over 76% of India's population
Using a composite Heat Risk Index (HRI) developed for 734 districts, the CEEW study identifies Delhi, Andhra Pradesh, Goa, Kerala, Maharashtra, Gujarat, Rajasthan, Tamil Nadu, Karnataka, and Uttar Pradesh as the 10 most heat-risk-prone states and Union Territories. The report is based on 35 indicators including frequency of very hot days, warm nights, rising humidity, population exposure, urbanisation trends, and health vulnerabilities.
One of the study's most alarming findings is the rapid increase in very warm nights—defined as nights where minimum temperatures exceed the 95th percentile of historical norms. Over the past decade (2012–2022), nearly 70% of districts saw at least five more such nights per summer compared to the 1982–2011 average. In contrast, only 28% of districts experienced similar increases in very hot days.
Cities are bearing the brunt. Mumbai saw 15 additional very warm nights, Bengaluru 11, Bhopal and Jaipur 7 each, Delhi 6, and Chennai 4. This trend is largely attributed to the urban heat island effect, where concrete-heavy infrastructure traps heat during the day and releases it at night.
'Very warm nights prevent the human body from recovering after intense daytime heat. This significantly increases the risk of heat strokes and exacerbates conditions like hypertension and diabetes,' said Dr Vishwas Chitale, Senior Programme Lead at CEEW and co-author of the report.
The report also highlights a growing secondary risk: increasing relative humidity. The agriculturally dense Indo-Gangetic Plain has witnessed up to a 10% rise in humidity over the past decade. Cities traditionally considered dry, such as Delhi, Chandigarh, Kanpur, and Varanasi, are now recording humidity levels that push the 'felt' temperature several degrees above the actual reading.
'High humidity hampers the body's natural cooling mechanism—sweating—and elevates health risks even during moderately hot days,' said Arunabha Ghosh, CEO of CEEW. 'We're entering an era of prolonged heat, rising humidity, and dangerously warm nights. The science is unequivocal—we must act now.'
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Indian Express
03-07-2025
- Indian Express
Heat health risks need to be understood as a slow, protracted disaster
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Instituting any surveillance system such as the National Heat-Related Illness and Death Surveillance is a complex task and we now have about a decade's experience and learning. The NCDC's evaluation, the 2024 report titled 'Heat-Health Preparedness & Response Activities, National Programme on Climate Change & Human Health', provides rich insights. The surveillance system collects aggregate data on heatstroke cases and deaths, emergency department attendance, cardiovascular and total deaths from all states and union territories from primary health centres and above. There were 48,156 Suspected Heatstroke Cases (SHC), 269 Suspected Heatstroke Deaths (SHD) and 161 Confirmed Heatstroke Deaths (CHD) in 2024 with reported increases in key daily indicators – emergency visits, total and cardiovascular deaths in the facilities. There has been a significant increase in reported SHCs over the last couple of years: 4,481 in 2022 and 19,402 in 2023 – the mark of a maturing surveillance system. Emergency attendance in the Reporting Units (RUs) increased from 3.6 million in 2022 to 30 million in 2024; total deaths in the facility from 86 to 74,216 and confirmed cardiovascular deaths (linked to HRIs to some extent) from 47 to 2,173. What is the robustness of HRI reporting? Reporting by the constituent units exhibit an expected seasonality: 20 per cent in March to 40 per cent in July; and the peak between May 15 and June 10 comprising nearly two-thirds (62 per cent) of the annual cases correlated both with peak heatwave days and dips during the holidays and weekends. In terms of consistency of daily reporting, Gujarat, Telangana and Odisha are the better performers. The NHRIDS had 47,477 Reporting Units (RU) in 2024 and 55 per cent reported HRIs. The top three states were also Gujarat, Odisha, Telangana with 91 per cent, 89 per cent and 72 per cent of the RUs reporting respectively. Contrast this with 23 per cent of the 40,390 RUs reporting in 2023. 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Indian Express
07-06-2025
- Indian Express
How extreme heat is affecting India
Around 76% of India's population is currently at high to very high risk from extreme heat, according to a new study. People living in Delhi, Maharashtra, Goa, Kerala, Gujarat, Rajasthan, Tamil Nadu, Andhra Pradesh, Madhya Pradesh, and Uttar Pradesh face the highest risk from heat in the country, the analysis suggests. The study, 'How Extreme Heat is Impacting India: Assessing District-level Heat Risk', was published on May 20. It was carried out by Council on Energy, Environment and Water (CEEW) researchers: Shravan Prabhu, Keerthana Anthikat Suresh, Srishti Mandal, Divyanshu Sharma, and Vishwas Chitale. For their analysis, the researchers developed a heat risk index (HRI), which assessed heat risk across 734 districts in India. The index is based on 35 indicators, including an increase in frequency of very hot days, population density, percentage of persons with disability, and change in land use and land cover. Understanding heat risk Contrary to common perception, heat risk is quite different from heat waves and heat stress. While heatwaves — they do not have any universal definition — usually refer to prolonged periods of abnormally high temperatures in a specific region, heat stress is when the body temperature exceeds 37 degrees Celsius in humans and animals. At this temperature, the body is not able to effectively remove excess heat, which can lead to discomfort, heat cramps, and exhaustion. If the body temperature crosses 40 degrees Celsius, a heat stroke can occur. Heat risk, on the other hand, is essentially the probability of experiencing heat-related illnesses or death due to exposure to extreme temperatures. It depends on three crucial factors: 'the intensity of the heat (and its compounding effects such as humidity); the degree of exposure; and the underlying vulnerabilities of affected communities,' according to the CEEW study. Factors driving heat risk RISE IN NUMBER OF VERY WARM NIGHTS: In the years between 2012 and 2022, the number of very warm nights has increased faster than very warm days, the study found. More than 70% of districts witnessed five or more additional very warm nights per summer (March to June) during this period. 'These nights and days are defined as periods when minimum and maximum temperatures rise above… what was normal for 95% of the time in the past,' it said. This is concerning because higher temperatures during the night make it difficult for the body to cool down after intense daytime heat, which can lead to a rise in health risks such as heat strokes and worsening of non-communicable diseases like diabetes and hypertension. INCREASE IN RELATIVE HUMIDITY IN NORTH INDIA: The study found out that between 2012 and 2022 the relative humidity — the amount of water that is present in the air compared to the greatest amount it would be possible for the air to hold at that temperature — has significantly increased in North India, particularly in Indo-Gangetic Plain. While North India used to have around 30–40% relative humidity during the baseline period between 1982 and 2011, it increased to 40-50% between 2012 and 2022. Higher relative humidity is an issue as it exacerbates heat stress on the human body, especially during the peak summer months. This happens because high relative humidity makes it harder for the body to cool down through sweat after the body temperature crosses 37 degrees Celsius. 'This can increase the occurrence of several heat-related illnesses at a faster rate,' the CEEW study said. HIGH POPULATION DENSITY & INCREASE IN URBANISATION: Apart from very warm nights, very warm days, and relative humidity, several other factors also influence heat risk. For instance, the study found that districts with high population density such as Mumbai and Delhi face the highest exposure to extreme heat. Districts, especially tier II and III cities such as Pune, Thoothukudi and Gurugram, which have seen rapid urbanisation in recent years have witnessed hotter nights. That is because of the emergence of concrete infrastructure which absorbs a lot of heat during the day and releases it during the night. Districts in states such as Andhra Pradesh, Maharashtra, Haryana, Punjab, Chhattisgarh, Bihar, and Uttar Pradesh are highly vulnerable to extreme heat. This is due to the combined impact of high temperatures and socio-economic and health vulnerabilities such as more elderly people and a high prevalence of non-communicable diseases like diabetes, according to the study. The significance The year 2024 was the warmest year on record for the world, including India. While the global average annual mean temperature during the year was more than 1.5 degrees Celsius higher than pre-industrial levels (1850-1900 period), the temperature over India in 2024 was about 1.2 degrees Celsius higher than the 1901-1910 average. Although the temperature rise in India is lower than the increase over the world, the country is already witnessing adverse effects of global warming. For instance, in 2024, India saw its longest recorded heatwave since 2010. There were more than 44,000 cases of heatstroke in the country last year. The situation has been worsened as India's heat action plans (HAPs) — early warning systems and preparedness plans for extreme heat events — remain lacking in some ways. 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The Hindu
01-06-2025
- The Hindu
Tamil Nadu among top heat-risk States in country; warmer nights put people at risk
Tamil Nadu is increasingly at risk from extreme heat events, as 2024 was the hottest year on record globally and India endured its longest heatwave since 2010. According to a recent study by the Council on Energy, Environment and Water (CEEW), Tamil Nadu ranks fifth among Indian States with high to very high heat risk, with urban centres like Chennai experiencing significant challenges from rising temperatures. In fact, none of Tamil Nadu's districts falls under the very low or low heat risk categories. About 11% districts face moderate heat risk, while 43% are classified as high risk, and 46% districts fall into the very high heat risk category, indicating that the majority of the State is confronting severe and widespread heat vulnerability. As per the study, over the past decade, heatwaves in Tamil Nadu's districts have lengthened by over three days, which has intensified impacts on public health, agriculture, and energy infrastructure. Chennai has witnessed an increase of four additional 'very warm' nights per summer, driven largely by the urban heat island effect, where cities retain heat well into the night. Warming nights a rising concern According to the CEEW study, national data from 1981 to 2022 shows that the frequency of very warm nights is increasing faster than very hot days, particularly in the last decade. Both terms refer to temperatures exceeding the 95th percentile of historical records. This trend is influenced by natural climate cycles such as El Niño and La Niña. For example, during strong El Niño years like 1997 and 2016, very hot days and very warm nights were significantly more frequent. Experts highlight that rising nighttime temperatures are especially dangerous because they prevent the body from cooling and recovering after hot days, increasing health risks for vulnerable groups such as the elderly and children. In Tamil Nadu, as in Punjab, West Bengal, Kerala, and Karnataka, vulnerability to heat is further exacerbated by the high prevalence of non-communicable diseases such as hypertension and diabetes. These conditions increase the risk of heat-related illnesses, placing additional strain on the State's healthcare system, the study points out. The study recommends that States, districts, and cities should move beyond a narrow focus on daytime temperatures while planning for heat risk and incorporate additional dimensions of warm nights, humidity, demographic patterns, and health vulnerabilities.
