Heatwaves
Science, Attribution, and IMD Definition
A heatwave is a period of abnormally high temperatures that can cause health emergencies. In India, the IMD (India Meteorological Department) defines a heatwave as: temperatures of 40°C or above in the plains (or 30°C in hilly regions), with the departure from normal being at least 4.5°C for "heat wave" and 6.5°C for "severe heat wave." Globally, heatwaves have increased in frequency, intensity, and duration due to anthropogenic climate change — a causal link now established by climate attribution science.
- Climate attribution: the field of science (pioneered by the World Weather Attribution consortium) that quantifies how much more likely an extreme weather event is due to climate change. European heatwaves are now found to be 2–5 times more likely due to human-caused warming.
- Urban Heat Island (UHI) effect: cities amplify heatwaves due to heat-absorbing surfaces and reduced vegetation.
- Health impacts: heat stroke, cardiovascular failure, respiratory distress; the elderly, outdoor workers, and children are most vulnerable.
- IMD heatwave criteria (plains): Max temp ≥40°C AND departure from normal ≥4.5°C (Heat Wave) or ≥6.5°C (Severe Heat Wave).
- European heatwaves are occurring in a continent that historically had mild summers — infrastructure (housing, hospitals) was not designed for extreme heat.
● Tracked since March 27, 2026 · last seen June 25, 2026 · updates as the daily brief publishes
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