'Wet-Bulb' Threshold: The Invisible Number Making India’s Scorching Heatwave Even Deadlier

Key points

• 'Wet-Bulb' Threshold: The Invisible Number Making India’s Scorching Heatwave Even Deadlier Written By, Last Updated: May 20, 2026, 07:00 IST The intersection of geography, urban architecture, and socioeconomic vulnerability makes India uniquely exposed to wet-bulb disasters A dry 45°C day in the desert expanses of Rajasthan can actually be safer than a muggy 38°C afternoon in Kolkata or Mumbai.
• Representational image As a punishing heatwave tightens its grip across the Indian subcontinent, traditional thermometers are failing to capture the true scale of the danger.
• Mercury levels regularly breach 44°C in the northern plains, forcing the India Meteorological Department (IMD) to issue rolling heatwave alerts.
• However, climate scientists and public health officials are urgently tracking a much more lethal, invisible metric: wet-bulb temperature.
• Unlike standard air temperature, wet-bulb temperature measures the compounding impact of heat and ambient humidity.