Simply Put: India warming
India's landmass has warmed by approximately 0.9°C during 2015–2024 relative to the 1901–1930 baseline — above the global average land warming — with northern India warming at 0.2°C per decade over the past three decades.
Heatwave frequency, intensity, and duration have all increased: "warm days" (exceeding the 90th percentile temperature) are rising by 5–10 days per decade across most regions, with northwest, northeast, Thar-Rajasthan, and peninsular India most affected.
The hottest days in western India and the northeast are now 1.5–2°C warmer than in the 1950s; pre-monsoon cyclone wind speeds have intensified by 40% and post-monsoon by 20%.
Southwest monsoon rainfall has shown a declining trend of 0.5–1.5 mm/day per decade over the Indo-Gangetic plains and northeast India during 1951–2024, while central India experiences increased extreme precipitation events (>150 mm daily).
IMD forecasts for April–June 2026 flag above-normal heat wave duration and warm nights nationwide, with the 2026 monsoon projected at approximately 92% of the Long Period Average.
The Hindu Kush Himalayan region has warmed by 0.28°C per decade (1951–2020) with elevations above 4 km warming at 0.34°C per decade — threatening India's glacier-fed rivers and water security.
IMD Heatwave Definition and Heat Action Plans
The India Meteorological Department (IMD) defines a heatwave as a condition when the maximum temperature of a station reaches at least 40°C for plains (30°C for hilly regions) AND departs by 4.5°C or more from normal. A severe heatwave is declared when the departure is 6.5°C or more from normal.
Key Details
- IMD Heat Warning colours: Yellow (watch), Orange (alert), Red (action required).
- Ahmedabad (Gujarat) implemented India's first — and Asia's first — city-level Heat Action Plan (HAP) in 2013 following a severe 2010 heat event that killed over 1,300 people; it reduced heat mortality by approximately 30%.
- NDMA (National Disaster Management Authority) issued national heatwave guidelines in 2019 covering early warning systems, inter-agency coordination, and public communication.
- India's National Action Plan on Climate Change (NAPCC, 2008) includes the National Mission on Strategic Knowledge for Climate Change as one of eight missions.
India's accelerating warming trend makes Heat Action Plans critical policy instruments; the Ahmedabad model has become the template for cities across South Asia.
Wet-Bulb Temperature and Human Heat Tolerance
Wet-bulb temperature (WBT) measures temperature while accounting for humidity, reflecting the cooling effect of evaporation. It is a key physiological stress metric because the human body cools primarily through sweat evaporation.
Key Details
- A WBT of 35°C is considered the theoretical limit of human survivability — at this threshold, even a healthy, resting adult in the shade cannot cool themselves sufficiently and will die within 6 hours without external cooling.
- WBT of 31–33°C is the practical threshold for dangerous outdoor labour, particularly for construction workers, agricultural labourers, and outdoor workers.
- India's coastal states (Kerala, Odisha, West Bengal, coastal Andhra Pradesh and Tamil Nadu) face combined heat-humidity risks that bring WBT levels close to dangerous thresholds during summer.
- IPCC AR6 (2021) identifies South Asia as one of the regions most at risk from fatal heat stress events by mid-century under a 2°C warming scenario.
India's rising temperatures combined with high humidity in coastal and eastern regions are pushing WBT values toward dangerous thresholds, with severe consequences for labour productivity and public health.
Himalayan Glaciers: The Third Pole
The Hindu Kush-Himalaya (HKH) region is home to the largest concentration of glaciers outside the polar regions, often called the "Third Pole." These glaciers feed 10 major river systems — including the Indus, Ganges, Brahmaputra, Mekong, Yangtze, and Yellow Rivers — providing water to approximately 1.9 billion people.
Key Details
- India has 9,775 glaciers covering approximately 71,782 sq km across the Himalayas and Karakoram.
- HKH glaciers have lost 40% of their volume since the 1970s according to ICIMOD (International Centre for Integrated Mountain Development) assessments.
- HKH region has experienced cumulative warming of approximately 2°C over the past 70 years — at rates of 0.34°C/decade above 4,000 m elevation.
- "Peak water" phenomenon: glacier retreat initially increases river flows as melt accelerates, followed by long-term decline as glaciers disappear.
- Glacial Lake Outburst Floods (GLOFs): accelerating glacier melt creates glacial lakes prone to sudden catastrophic outbursts, threatening downstream communities in Himachal Pradesh, Uttarakhand, Sikkim, and Arunachal Pradesh.
The observed acceleration in HKH warming directly threatens the long-term water security of the Indo-Gangetic plains and peninsular rivers that depend on snowmelt, particularly during lean (non-monsoon) seasons.
India's Monsoon System and ENSO-IOD Connections
India's southwest monsoon (June–September) delivers approximately 70–90% of India's annual rainfall and is critical for agriculture, groundwater recharge, and hydropower. The monsoon is modulated by global climate patterns including El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD).
Key Details
- El Niño (warming of central-eastern Pacific) typically suppresses Indian monsoon rainfall; La Niña (cooling of Pacific) typically enhances it.
- Positive IOD (warmer western Indian Ocean) generally counteracts El Niño's suppressive effect on the monsoon.
- Mean southwest monsoon rainfall over the Long Period Average (LPA): 88 cm; 2026 is projected at approximately 92% of LPA (below normal).
- North-west India has seen rainfall increases of 60–120 mm per decade since the 1950s, while the Indo-Gangetic plains show declining rainfall trends.
- Western Disturbances (extratropical cyclones originating over the Mediterranean) are the primary precipitation mechanism for northern India in winter, supplying critical snowpack to the Himalayas.
Monsoon variability, combined with accelerating warming, creates compounding risks for Indian agriculture — both droughts and intense precipitation events are increasing simultaneously in different parts of the country.
- India's warming: ~0.9°C during 2015–2024 vs 1901–1930 baseline; northern India at 0.2°C/decade.
- Global warming as of 2026: approximately 1.3°C above pre-industrial levels.
- HKH warming: 0.28°C/decade (1951–2020); above 4 km: 0.34°C/decade.
- India's glaciers: 9,775 glaciers, 71,782 sq km total area.
- IMD heatwave definition: ≥40°C (plains), ≥30°C (hills), departure ≥4.5°C above normal.
- WBT threshold for unsurvivable conditions: 35°C (for 6+ hours without cooling).
- India's per capita freshwater availability: approximately 1,486 cubic metres/year (2021), below the 1,700 cubic metres water stress threshold.
- North Indian Ocean sea level rise: 3.3 mm/year (1993–2015); 2–3 fold increase in extreme sea level events (1995–2019).
- Monsoon Long Period Average: 88 cm; 2026 projection: ~92% of LPA (below normal).
- Ahmedabad Heat Action Plan (2013): first in Asia; reduced heat-related mortality by ~30%.
- Pre-monsoon cyclone wind speed intensification: 40%; post-monsoon: 20%.
- Marine heatwave days projected: from 20 days/year (1970–2000) to ~200 days/year by 2050.