CHENNAI: The state has introduced a localised, colour-coded heat early warning system as Chennai and several interior districts, until recently, faced an unusually prolonged heat spell, marked by high daytime temperatures and warm nights that offer little relief.
Chennai’s Meenambakkam observatory recorded 40°C or above on nine of the first 10 days of June, coming close to the extreme of 2024 when the city logged 13 such days between June 1 and 17. The day-time temperature, from June 11, dropped below normal, thanks to the recent thunderstorms.
The State Heat Action Plan 2026 proposes district-specific thresholds associated with health impacts and response actions, recognising that conventionally declaring heat waves may overlook local risks. For Chennai, four alert categories have been identified. Temperatures below 37°C fall in the normal range.
A Yellow Alert kicks in at 37°C-39°C, signalling moderate heat stress. An Orange Alert applies from 39°C-41°C, requiring preparedness measures from departments. A Red Alert is proposed above 41°C, when emergency response may be activated.
“While IMD issues warnings to the public, our warnings are sent to urban local bodies and district administrations. We started sending them from May,” a senior SDMA official told TNIE. The state is also developing a daily heat report to be disseminated down to the taluk and ward levels. There are also plans for an AI-enabled platform integrating weather, health, humidity and sector-specific vulnerability data.
Since June 3, minimum temperatures at night in Chennai have stayed above 30°C, touching 31.4°C on June 9, which is considered unusual and possibly dangerous because it prevents the body from recovering from daytime exposure.
The Heat Action Plan notes warm nights are increasing faster than hot days across Tamil Nadu. The average number of very warm nights has risen from around six a year during the 1982-2011 baseline to about 13 annually in the last decade, while very hot days moved from six to eight.
Rising humidity, up by as much as six percentage points in parts of the state, is also compounding heat stress, making conditions feel hotter than recorded temperatures. Combined with urban heat island effects, the risks are highest for outdoor workers, children, senior citizens and those with pre-existing conditions.