CHENNAI: Tamil Nadu has increasingly been at the receiving end of extreme heat as climate change intensifies temperatures and urban expansion worsens the impact, according to a new report by the Council on Energy, Environment and Water (CEEW).
The study warns that Tamil Nadu has emerged among the top 10 states in India that face the highest overall heat risk, combining rising heat hazards with the vulnerability of its 7.2 crore residents.
While Tamil Nadu has long experienced scorching summers during the ‘agni nakshatram’ period, the report suggests that the heat is no longer just a seasonal challenge.
Instead it is becoming a persistent and growing climate threat affecting health, livelihoods and urban living conditions.
The CEEW study assessed 734 districts across India using a Heat Risk Index (HRI) that measures three key factors — hazard, exposure and vulnerability.
Hazard refers to the intensity and frequency of heat events. Exposure measures how many people and infrastructure are located in high-heat zones. Vulnerability reflects how sensitive communities are to heat and their ability to cope.
Tamil Nadu's ranking is driven by a combination of rising temperatures, rapid urbanisation and a high prevalence of non communicable diseases.
One of the most concerning trends highlighted in the report is the rise in ‘very warm nights.’ Between 2012 and 2022, Chennai experienced four additional very warm nights each summer, compared to historical averages.
Cities such as Chennai, Madurai and Tiruchy are witnessing this phenomenon, where heat absorbed during the day is slowly released at night.
This has serious health implications. Nights are crucial for the human body to recover from daytime heat exposure. When night temperatures remain extremely high above the 95th percentile, the body struggles to cool down, increasing the risk of heatstroke and aggravating conditions such as hypertension and diabetes.
The report notes that Tamil Nadu's public health profile further amplifies the threat. The state has a significant number of people suffering from non-communicable diseases such as diabetes and anaemia, which increases sensitivity to heat stress.
At the same time, the economic consequences are equally worrying. India could lose the equivalent of 35 million full time jobs by 2030 due to heat stress, the study estimates.
In Tamil Nadu, where a large number of people work in construction and informal sectors, the productivity loss from extreme heat is already becoming visible. Outdoor workers including farm labourers, street vendors and construction workers are among the most vulnerable.
Unlike northern states, Tamil Nadu's coastal geography already exposes it to high humidity levels of around 60-70% during summer.
When high humidity combines with rising temperatures, sweating, which is the body's natural cooling mechanism, becomes less effective. As a result, the "feels-like" temperature becomes much higher than the recorded temperature, increasing the risk of dehydration, heat exhaustion and organ stress.
The CEEW report emphasises that while the hazard is increasing, the risk can be reduced through stronger adaptive strategies.
Key measures suggested include district level Heat Action Plans to identify local vulnerabilities and improve preparedness, nature-based solutions including expanding urban green cover and restoring water bodies, improved access to electricity and drinking water, and financial protection mechanisms such as parametric insurance for outdoor workers affected by extreme heat.
Speaking to DT Next, Dr Amudha, Director of the Regional Meteorological Centre (RMC), Chennai said people who remain outdoors for long hours or perform heavy physical work are at greater risk of heat-related illnesses.
Children, elderly people and individuals with chronic diseases are particularly vulnerable to heat stress, she said.
She advised the public to take precautionary measures such as avoiding prolonged exposure to direct sunlight, drinking sufficient water even if they do not feel thirsty, using ORS or homemade drinks such as lassi, rice water, lemon water and buttermilk, wearing light-coloured loose cotton clothing, and covering the head with a cloth, hat or umbrella.
"These advisories are issued by the India Meteorological Department (IMD), State Disaster Management Authority (SDMA) and the Government of Tamil Nadu as part of heat-wave preparedness measures, " she said.
According to the IMD, a heat wave is declared when maximum temperatures reach at least 40°C in plains, 37°C in coastal areas and 30°C in hilly regions.
Heat waves are classified based on two criteria. Based on departure from normal temperature, a heat wave is declared when temperatures are 4.5°C to 6.4°C above normal, while a severe heat wave is declared when temperatures are more than 6.4°C above normal.
Based on actual maximum temperature for plains, a heat wave is declared when temperatures reach 45°C or more, while a severe heat wave is declared when temperatures reach 47°C or more.
To declare a heat wave, these conditions must be recorded at two stations in a meteorological sub-division for at least two consecutive days and it will be declared on the second day.
For coastal stations, heat wave conditions may be described when the maximum temperature departure is 4.5°C or more from normal, provided the actual maximum temperature is 37°C or more.
Dr Amudha said the RMC Chennai regularly issues special bulletins regarding realised and expected maximum temperatures for the subsequent two to five days. Warnings for hot and humid weather are also issued whenever necessary.Special bulletins are issued during such situations, she added.
"For coastal stations, sea breeze influences reduction in maximum temperature, which sets in around 2.30 pm to 3 pm. Later, the sea breeze sets in and the temperature starts reducing" she said.
She also noted that the heat wave mitigation plan will be submitted to the Election Commission during the election process to ensure preparedness.
Meanwhile, climate activist Vetri Selvam from Poovulagin Nanbargal said global warming is intensifying extreme heat across many regions including India, the Middle East and Africa.
"In India, improper land use patterns are also contributing to the problem, " he said.
According to him, the United Nations recommends that only 60 percent of land should be used for human activities while the remaining 40 percent should be maintained as forests.
"But in India forest cover is only about 24 percent, and in Tamil Nadu it is just around 21 percent, " he pointed out.
He also warned that encroachment of water bodies and shrinking water surfaces further intensify heat impacts.
Vetri noted that Chennai has one of the lowest green cover levels among Indian cities, increasing its vulnerability to rising temperatures.
He also suggested that India adopt the Universal Thermal Climate Index (UTCI), a system widely used in the European Union, for better assessment of heat stress.
Additionally, he urged authorities to record heat-related deaths more accurately.
"If a person dies due to heat stress, the death certificate should mention 'heat-induced cardiac attack'. Only then can we obtain reliable data on heat related deaths, " he said.
As Tamil Nadu faces rising temperatures, the report serves as both a warning and a roadmap. Extreme heat is no longer a distant climate concern but an immediate challenge affecting public health, urban living and economic productivity across the state.