Desk Correspondent , New Delhi — The India Meteorological Department (IMD) is significantly revising its heat wave warning system by introducing a percentile-based threshold to better capture dangerous, humid conditions in coastal regions. Under the new framework, a heat alert will be triggered when maximum temperatures exceed the 95th percentile—the point above which only 5% of historically recorded temperatures fall for a given location. This shift marks a major departure from existing guidelines that rely strictly on absolute temperature spikes, which frequently failed to flag the oppressive heat of coastal areas where high humidity compounds the health risks despite lower thermometer readings.

Currently, the IMD issues heat wave warnings for plains at 45°C and coastal areas at 37°C, provided temperatures are at least 4.5°C above normal. The new system bypasses these rigid limits, allowing meteorologists to issue timely alerts without waiting for absolute thresholds to be breached. Climate scientists have welcomed the decision, noting that percentiles are far more effective at defining localized extremes irrespective of the background mean temperature. The update arrives as India braces for a punishing summer, with the World Meteorological Organisation predicting an 80% chance of an El Niño event developing between June and August 2026.

The revision aligns with evolving climate science on wet-bulb temperatures, which measure how effectively the human body cools itself through sweat. While air temperatures in coastal South India rarely hit the mid-40s, high humidity stops sweat from evaporating, pushing the body toward dangerous heat stress. While the historical survival threshold for wet-bulb temperature was thought to be 35°C, recent physiological studies suggest the actual limit where the human body can no longer cool itself is closer to 31°C, making the updated localized warning system vital for public safety.