IMD to revise heatwave criteria as climate change intensifies extreme heat

India’s India Meteorological Department (IMD) is revising its heatwave declaration criteria to address gaps in current guidelines, which fail to capture severe heat stress in regions like Kerala. The existing rules require temperatures to exceed 37°C in coastal areas, 40°C in plains, or 30°C in hilly regions—alongside a 4.5°C deviation from normal—before issuing alerts. However, Kerala experienced extreme heat and humidity this summer due to a rare anti-cyclonic system near the Karnataka–Maharashtra coast, trapping warm air and causing nighttime temperatures 3–4°C above normal. The IMD’s current system also mandates simultaneous heat recordings at two stations within a state, a condition rarely met in Kerala despite dangerous heat stress levels. As a result, authorities have issued only ‘hot and humid weather’ advisories instead of heatwave warnings, despite multiple heatstroke cases. Climate experts classify Kerala as a climate hotspot, citing rising temperatures, erratic rainfall, and shifting monsoon patterns. The revised framework, developed with technical partners and disaster management authorities, aims to issue earlier and more effective warnings for humidity-driven heat risks. Officials note that traditional temperature thresholds often underrepresent health dangers in humid climates. The IMD has also forecast a below-normal monsoon this year, citing back-to-back El Niño years—a first in India—which heightens concerns over prolonged heat and irregular rainfall. The new criteria will better reflect India’s evolving climatic realities, ensuring public safety measures align with emerging heat stress risks. Kerala’s experience underscores the need for adaptive policies as climate change intensifies extreme weather events.