Tamil Nadu among top heat-risk States in country; warmer nights put people at risk

Chennai has witnessed an increase of four additional “very warm” nights per summer, driven largely by the urban heat island effect, says study. | Photo Credit: VEDHAN M

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 95^th 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.

Published - June 01, 2025 09:29 pm IST