Beyond high temperatures: understanding heat stress in Tamil Nadu

For Tamil Nadu, peak summer traditionally ends in May. But this season, temperatures hovering around 40 degrees Celsius in several districts have extended burning conditions into June, leaving residents to contend with grueling days and uncomfortably warm nights. Clearly, the time has come to move beyond seasonal, boilerplate responses. It is against this backdrop that the state recently unveiled its Heat Action Plan 2026, which introduces measures such as local heat vulnerability mapping, early warning systems and targeted interventions for vulnerable communities. At the same time, meteorologists are keeping a close eye on the tropical Pacific for a strengthening El Nino that could affect weather, precipitation and heat risks in the coming months. From outdoor workers and children to the elderly in dense urban areas, rising temperatures and heat stress are a real test of endurance for everyone.

Selvam, a rig worker who spends most of the day navigating Chennai’s roads to complete deliveries, says access to potable water remains a challenge. “I’m wary of drinking water from public kiosks, so I carry a water bottle, but it runs out within an hour. I either ask for refills at the places I deliver to, or rely on buttermilk distributed by residents and temples,” he said.

Meteorologists said that May 2026 was significantly warmer than normal in many parts of Tamil Nadu and among the warmer recent Mays, with inland areas experiencing sustained heatwave-like conditions. Observations by the Regional Meteorological Center (RMC) indicate that Vellore recorded the season’s highest temperature of 42.5 degrees Celsius on May 22, followed by Tiruttani and Meenambakkam in Chennai. With temperatures peaking above 40 degrees during the last fortnight of May, the persistent heat has led to moderate to severe heat stress and increased discomfort in many districts. RMC officials noted that the hot weather was due to strong pre-monsoon solar heating, dry continental air prevailing over interior parts and delay in widespread southwest monsoon activity. The urban heat island (UHI) effect further intensified temperatures in densely populated areas.

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Vulnerable inner neighborhoods

While factors such as inland location, limited influence of sea breeze and semi-arid conditions make the northern interior and central interior most vulnerable to heat stress, the coastal Chennai metropolitan area (CMA) faces another heat-related problem due to high humidity and the UHI effect. A temperature of 37 degrees Celsius with high humidity can be more stressful for the human organism than 40 degrees Celsius in a dry state. Other meteorological factors also played a role in the warm nights at coastal locations, including cloud cover, rising humidity and wind patterns.

VR Durai, director of the Regional Weather Forecasting Centre, RMC, points out that heatwave-like conditions have become more frequent, longer-lasting and more intense over the past decade, in line with trends in India, and says hot weather spells are becoming permanent with consecutive days of 40-degree temperatures often seen in inland districts like Salem, Erode and Madura, Tiruchi.

YEA Raj, former Deputy Director General of Meteorology, RMC, attributes the persistent heat in Tamil Nadu during June to strong westerlies and reduced monsoon cloud cover, which led to high temperatures that did not drop much during the night hours at many places. The rain shadow state tends to experience intense heat when storm cloud activity is absent. Heat stress varies with humidity levels that change throughout the day. Due to equally high temperature in Pamban and Madurai, the degree of discomfort may vary depending on the humidity. While the India Meteorological Department (IMD) observations are conducted under sheltered conditions, those outside may experience warmer temperatures and denser population and traffic further contribute to the UHI effect, he says.

The combined effects of climate change, urbanization and natural climate variability have increased the likelihood of extreme heat, underscoring the need for effective heat plans and early warning systems, meteorologists say.

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Intense summer heat

According to the RMC, Tamil Nadu has witnessed a series of intense summer heatwaves in the past decade, with temperature records indicating a clear concentration of extreme heat in the north and interior. The worst heat episodes of the decade occurred during May 2017 and May 2024. The data suggests that northern and inland Tamil Nadu continues to be the epicenter of extreme summer heat, with Vellore (which recorded the decade’s highest May temperature of 43.7 degrees Celsius) remaining a prominent hotspot over the past decade. As more districts experience high temperatures and warm nights, heatwaves are emerging as one of the state’s significant weather-related hazards.

Although Tamil Nadu experienced cooler temperatures than Telangana, coastal Andhra Pradesh and northern India, widespread 40-degree temperatures and high humidity intensified heat stress, especially along the coast. Intense heat waves in Telangana resulted in 48 heat-related deaths. According to Mr. Durai, no death has been reported in Tamil Nadu.

Mahesh Palawat, vice-president (meteorology and climate change), Skymet Weather Services, said Banda in Uttar Pradesh has emerged as one of the hottest places in the country this summer, recording temperatures as high as 48.3 degrees Celsius and the temperature staying above 47 degrees Celsius for several days. Interestingly, western Rajasthan, traditionally India’s hottest region during summer, did not experience extreme temperatures this year. Instead, severe heat was concentrated over southwest Uttar Pradesh, parts of Madhya Pradesh, Marathwada and Vidarbha during May, he said.

IMD data indicates that average summer temperatures in hot weather areas of Tamil Nadu have increased by about 0.5 degrees Celsius to 0.9 degrees Celsius over the last 35 years. Karur and Tiruchi show the strongest warming trends. Even a small increase in average temperature can substantially increase the frequency of hot days, warm nights and heat stress conditions in such hotspots, officials say.

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Unpleasant weather

According to D. Sivananda Pai, Head, RMC, unpleasant hot weather has increased in recent years due to global warming. The UHI effect contributed to the discomfort, creating a difference of 4 to 5 degrees Celsius in real-world temperatures between urban and nearby open areas. Land use and land cover changes are also triggers. Sea surface temperature anomalies in the tropical Pacific indicate a warming trend that may intensify from July. The Monsoon Mission Coupled Forecast System suggests further strengthening of El Nino conditions during the southwest monsoon, potentially reaching moderate to strong intensity. This may affect the warm temperatures in Tamil Nadu in September. Its effect may extend until 2027, potentially leading to a warm winter next year. It is normally associated with a good northeast monsoon. However, each year is unique and there have been exceptions in the past, says Mr Pai.

Mr. Palawat also notes that El Nino may not have any significant impact on Tamil Nadu and the southern peninsular region this year. Its high impact would be reflected in rainfall patterns over central parts of India in August and September.

While much of the heat management framework revolves around outdoor temperatures and daytime heat, a recent study in Chennai linking indoor temperatures and relative humidity by Climate Trends, a research consultancy and capacity-building initiative, found that residents face heat stress indoors even after the peak summer months. It documented persistent elevated nighttime temperatures. Indoor temperatures monitored in 50 households in Chennai between October 2025 and April 2026 were found to frequently exceed 32 degrees Celsius, and most experienced at least four months of continuous heat exposure. Indoor temperatures peaked between 20:00 and 21:00 as the concrete structures released heat accumulated during the day, and nighttime temperatures rarely fell below 31 degrees Celsius. The study also found that the structural characteristics of housing, including construction materials, played a decisive role in shaping indoor thermal conditions.

Heat waves were declared as a state-specific disaster in Tamil Nadu in 2024, facilitating the use of State Disaster Response funds for preparedness and relief. The notification also stipulated compensation for heat-related deaths and paved the way for a coordinated response involving health, disaster management and local government departments. Proposed relief measures included providing medical aid and oral rehydration salts and access to potable water in affected areas.

Meanwhile, the impact of rising temperatures is being felt across sectors. Outdoor workers, including construction and agricultural workers and street vendors, are among the most exposed to heat stress. A 2026 study titled “Quantifying the Impact of Heat Stress on Work Productivity Among Informal Outdoor Workers in South India,” led by researchers including Vidhya Venugopal and published in the journal Scientific Reports (Nature Portfolio), surveyed 1,560 outdoor workers in 11 districts of Tamil Nadu. Prolonged exposure to high temperatures has been shown to affect worker productivity and health, increase the risk of dehydration and heat-related illness, and put additional pressure on public health systems. “During summer, I start work early. But within a few hours, I start getting hot. I keep drinking water and taking short breaks… In the afternoon, I feel headache, fatigue and dizziness,” says R. Vimala, a construction worker from Sriperumbudur.

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State heat action plan

As part of efforts to strengthen preparedness, the Tamil Nadu State Disaster Management Authority and the Tamil Nadu Disaster Risk Reduction Agency have launched the State Heat Action Plan 2026. It focuses on localized risk assessment, instead of relying only on national averages, by mapping localized heat vulnerability and creating an industry-specific threshold mechanism. It aims to improve early warning systems, taluk-level heat thresholds and better coordination between government departments. Officials say district-level heat hazard bulletins will be issued daily.

For workers, recommendations include rescheduling outdoor work and ensuring access to potable water. In health, the plan calls for increased surveillance of heat-related illnesses and training of health workers. The agency also requested feedback via https://beta-tnsmart.rimes.int/index.php/Action_plan/HeatWave.

Retired bureaucrat K. Phanindra Reddy says that in the short term, awareness needs to be created about the dangers posed by heat waves and the precautionary measures that need to be taken, while the government takes measures to ensure the supply of drinking water to the vulnerable population and prepares line departments to proactively respond to emergencies. Restoration of water bodies and expansion of green cover must be a long-term countermeasure.

The IMD plans to increase the use of heat indices and heat stress monitoring rather than focusing solely on temperature. In addition to sharing an annual climate report with the Tamil Nadu government, it plans to incorporate a heat index during specific hours to measure thermal discomfort and a realistic indication of “real feeling” temperature. But campaigners point to a persistent gap between policy, planning and implementation. G. Sundarrajan of Poovulagin Nanbargal says, “There are enough scientific reports and action plans. But they remain only on paper.” It calls on the government to address the impact of UHI on the war footing by expanding urban green spaces. One possibility is the transplanting of mature trees into cities. Their survival rate may be around 50%-60% initially, but could improve with better management. Although climate change is a global challenge, solutions must be tailored to local conditions.

(With contributions from Geetha Srimathi and Dennis S. Jesudasan)