Heatwaves have become a recurring and intensifying climate phenomenon, both globally and in India. As per the World Meteorological Organization (WMO), 2024 was the warmest year on record, with global temperatures about 1.55°C above pre-industrial levels. India is witnessing an increasing frequency, duration, and intensity of heatwaves, which is a critical public health, economic, and equity challenge. Similarly, Europe has warmed almost twice as much as the global average, driven by multiple region-specific factors.
What are heatwaves? How are they defined in India?
Heat waves are prolonged periods of excessively hot weather that can cause adverse impacts on human health, the environment, and the economy. In India IMD defines heatwave based on the following criteria.
Physiography of regions
· Plain– The maximum temperature recorded at a station is 40 degrees Celsius or more.
· Coast- The maximum temperature recorded at a station is 37 degrees Celsius or more.
· Hills- The maximum temperature recorded at a station is 30 degrees Celsius or more.
Based on Departure from Normal Temperature
· Heat Wave- Departure from normal is 4.5°C to 6.4°C
· Severe Heat Wave- Departure from normal is >6.4°C
Based on Actual Maximum Temperature
· Heat Wave- When actual maximum temperature ≥ 45°C
· Severe Heat Wave- When actual maximum temperature ≥47°C
Heat Wave is declared if above criteria are met in at least 2 stations in a Meteorological subdivision for at least two consecutive days.
What are the causes and factors behind rising heatwaves?
A. Heatwaves in the Indian Subcontinent
Natural causes
1. High Atmospheric Pressure Systems- Heatwaves occur when high-pressure systems stall over a region. These systems trap warm air near the Earth’s surface and prevent the normal movement of air masses, leading to prolonged periods of hot weather.
2. Climate Variability- Natural climate variations, such as El Nino and La Nina events, influence weather patterns and increase the likelihood of heatwaves. For ex- During El Nino events, warmer ocean waters in the tropical Pacific lead to changes in atmospheric circulation and weather patterns.
3. Drought and Dry Conditions- Prolonged periods of drought and lack of precipitation reduces the overall moisture of the soil, causing the land to heat up more quickly during heat waves.
4. Changes in Wind Patterns- Shifts in wind pattern transports hot air from one region to another which intensifies heat waves in areas that are not typically prone to such extreme temperatures.
5. Geography and Topography- Geographic features and topographical conditions also contribute to the development of heat waves. For ex- Landlocked valleys and regions surrounded by mountains trap hot air and lead to temperature spikes.
Human-Induced Factors
1. Climate Change- India has warmed 0.7°C since pre-industrial levels, lower than the global land average (1.59°C), but the frequency of heatwaves has increased in the last two decades.
2. Urban Heat Island Effect- Urban areas with high population density, extensive concrete and asphalt surfaces, and limited vegetation tend to absorb and retain more heat, has created localized zones of higher temperatures. This phenomenon, known as the urban heat island effect, has intensified heat waves in cities.
B. Heatwaves in Europe
1. Greater Arctic Influence (Polar Amplification)- Europe, particularly the northern and eastern regions, lies close to the Arctic, where warming is 3-4 times faster than global average due to albedo loss from melting ice.
2. Cleaner Air & Reduced Aerosols- Reduction in air pollution leads to less aerosol-based sunlight scattering, increasing absorption of solar radiation.
3. Urbanization & UHI Effect- Densely populated European cities exacerbate warming.
4. Sea Surface Temperature Rise & Atmospheric Circulation- Warmer seas around Europe and altered jet stream patterns lead to prolonged summer heatwaves.
5. Albedo Effect (Europe/Arctic)- Melting Arctic ice exposes dark surfaces (land/water) that absorb more heat. The Arctic is warming 3 to 4 times faster than the global average, influencing European warming trends.
6. Climate Change- Anthropogenic greenhouse gas emissions are leading to global temperature rise, now nearing the 1.5°C threshold. Land areas (especially in mid- to high-latitude regions) are warming faster than oceans.
7. Warming Rate- Average annual temperature increased 2.4°C from pre-industrial times, compared to global 1.3°C. Longest-ever heatwave in Southeast Europe; lowest number of cold days.
What is the significance of curtailing Heatwaves?
1. Public Health Significance- When external temperature approaches 37°C, the human body struggles to release internal heat, resulting in heat stress affecting organs like kidneys, liver, and brain. Reducing hospital and emergency room burden improves health system efficiency.
2. Economic and Productivity Gains- Nearly 75% of India’s workforce (~380 million people) is employed in heat-exposed sectors like construction and agriculture. As per ILO estimates heat stress is estimated to result in a 3–5% GDP loss annually in countries like India. Protecting outdoor workers ensures continuity in farming, construction, logistics, and industrial sectors. It reduces loss of working hours, safeguards GDP.
3. Social Equity and Justice- The impacts of heatwaves are disproportionately felt by the poor, women, elderly, and migrant workers, making heatwave mitigation a key element in addressing social inequities. A people-centric approach protects the most vulnerable.
4. Climate Resilience and SDG Goals- Heatwaves are one of the most direct manifestations of climate change. Addressing them contributes to the global goal of mitigating climate change and reducing carbon emissions. Aligns with SDG 3 (Health), SDG 8 (Decent Work), SDG 11 (Sustainable Cities), and SDG 13 (Climate Action).
5. Mitigating Urban Heat Island (UHI) Effect- Curtailing heatwaves can enhance urban livability, lower energy consumption (through reduced air-conditioning needs), and improve the mental and physical well-being of city dwellers.
6. Reducing Environmental Stress and Ecosystem Damage- Curtailing heatwaves helps protect biodiversity, ensuring the health of ecosystems and natural resources essential for human survival.
What are the challenges in addressing heatwaves?
1. Early and Unpredictable Onset of Heatwaves- Heatwaves are now starting earlier in the year, catching authorities and populations off-guard. In 2025, severe heatwaves struck North and Central India 20 days earlier than in 2024, before HAP protocols were activated.
2. High Vulnerability of the Informal Workforce- Nearly 75% of India’s workforce (~380 million), especially in agriculture, construction, and street vending, is directly exposed to outdoor heat. In Odisha and Gujarat, many daily wage workers continued working in peak heat hours due to lack of income alternatives or workplace protections.
3. Economic and Productivity Losses- As per ILO and World Bank estimates (2023) heatwaves have a tangible economic cost, including loss of 3–5% of GDP and up to 6% of annual work hours. In sectors like agriculture and construction, heat-induced fatigue reduced work output and delayed infrastructure projects in Rajasthan and Telangana.
4. Unequal and Disproportionate Impacts- Marginalized groups—women, elderly, migrants, and the urban poor—face higher exposure with fewer coping mechanisms. Migrant families living in tin-roofed shelters in Delhi reported extreme indoor heat and health issues during April 2024.
5. Partial and Uneven Implementation of Heat Action Plans (HAPs)- While 140+ cities and 23 states have HAPs, many lack funding, inter-agency coordination, and local customization. A 2023 CEEW analysis found that only a handful of HAPs included cooling centres, outreach in local languages, or inter-departmental response mechanisms.
6. Insufficient Public Awareness and Risk Communication- Awareness about heatwave risks and protective behavior remains low, especially in rural and low-income urban areas. In Bihar, despite IMD warnings in 2024, many communities continued outdoor weddings and festivals in peak hours, leading to heat-related illnesses.
What Should be the Way Forward?
1. Strengthening and Expanding Heat Action Plans (HAPs)- Update HAPs in every State based on local vulnerability assessments. Include humidity, nighttime temperatures, and thermal comfort indexes for long term planning.
2. Data-Driven Decision Making- Collect granular, real-time heat morbidity and mortality data. Map hotspots within cities to identify intra-urban heat inequality.
3. Improve Early Warning and Forecast Systems- Introduce Heat Health Alert (HHA) systems as in the UK. Use predictive analytics for work timing adjustments in schools, factories, and offices.
4. Build Heat-Resilient Infrastructure- Promote cool roofs, white rooftops, reflective paint, better urban ventilation, and green corridors. Adopt heat-resilient building codes and zoning laws.
5. Protect Informal Workers- Allow staggered/shifted work hours. Provide financial support and insurance for wage losses during heatwaves.
6. Establish Cooling Shelters and Public Utilities- Develop summer shelters like winter shelters. Ensure availability of ORS, drinking water points, shaded rest areas.
7. Encourage Behavioral and Institutional Change- Public awareness campaigns, climate literacy, and workplace heat safety protocols.
8. Long-Term National Policy- Integrate heatwave resilience in National Disaster Management Plan, Smart Cities Mission, and urban master plans. Incentivize tree plantation, wetland conservation, and urban greening.
Conclusion
The rising threat of heatwaves in both India and Europe signals an urgent climate adaptation imperative. While Europe warms faster due to polar influence and cleaner air, India faces a distinct set of vulnerabilities driven by high outdoor labour dependence and inequality. The battle against heatwaves must move beyond token advisories and aim for science-based, people-centric, and equity-focused long-term planning. As the cost-effectiveness of heat adaptation is well-established, prioritizing this agenda is not only a climate responsibility but also a development necessity.
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