Warm nights, high humidity: Mumbai’s hidden heatwave threat, say experts

Mumbai: Even as hot and humid weather continues in Mumbai with a yellow alert in place over the last two to three days, it is the lack of relief at night that is also emerging as a key health concern, experts said, during an interaction on heatwaves on Thursday.Officials explained that heatwave conditions are no longer assessed by temperature alone. A combination of factors — including humidity, departure from normal temperatures, and the heat index — are now used to determine discomfort levels and issue colour-coded alerts. "For coastal cities like Mumbai, a heatwave is declared when temperatures reach 37°C or more along with a departure of at least 4.5°C above normal," said Bikram Singh, head India Meteorological Department (IMD) Mumbai and scientist, at the session hosted by Regional Meteorological Centre, Mumbai, in collaboration with the Mumbai Press Club and Asar Social Impact Advisors."Warm nights, where temperatures remain high even after sunset, are also a growing concern. Heatwaves are classified using colour-coded alerts for public understanding. Green indicates normal conditions, yellow signals caution, and red denotes severe heatwave situations. Heatwave alerts are being issued by us in advance, itself so that the message reaches everyone and especially the most vulnerable. This year, anti-cyclonic conditions over Maharashtra led to early warnings," he added.Addressing concerns over multiple heatwave warnings in March this year, officials clarified that the recent heat condition in Mumbai is not entirely unprecedented. Areas like Santacruz have recorded temperatures above 41°C in the past as well in the month of March, said Singh.On warm nights during summer months, Dr Pradeep Awate, former state surveillance officer of Maharashtra health services, explained that the human body does not get adequate time to recover from daytime heat stress. "The body stays in a constant state of thermoregulation, increasing health risks, especially for vulnerable populations like those who are a large part of the informal work force like construction labourers who work between 11am-4pm when the heat is at its peak," said Dr Awate.Experts also highlighted that acclimatisation plays a role in how populations respond to heat. "People living in consistently hot climates are more adapted, but sudden spikes or prolonged heat spells can still have serious impacts," said Dr Awate.Get real-time updates and result insights on the CBSE 12 Result 2026.