Heatwaves in India Explained

In official usage, heatwaves in India are spells of abnormally high daytime temperature, formally declared by the India Meteorological Department (IMD) when the maximum temperature reaches at least 40°C in the plains or 30°C in hilly regions and also departs sharply from the normal for that place and time of year. They occur mainly between March and June, before the southwest monsoon arrives, and they rank among the deadliest weather hazards the country faces.

This explainer covers how the IMD defines a heatwave, why spells are becoming longer and more frequent, which regions suffer most, how cities amplify the heat, what the health toll looks like and how Heat Action Plans and early warnings try to protect people. Information on this page was last reviewed on 15 October 2026.

Quick Facts: Heatwaves in India

Key Takeaways

• The India Meteorological Department declares a heatwave when the maximum temperature is at least 40°C in the plains or 30°C in hilly areas and is 4.5°C or more above normal.
• A severe heatwave in India is declared when the departure from normal exceeds 6.4°C, or when the actual maximum temperature reaches 47°C or more.
• Heatwave days in India have been rising over recent decades, and climate change is lengthening the season and raising peak temperatures.
• Urban heat islands can make Indian cities several degrees hotter than surrounding rural areas, especially at night, which removes the body’s chance to recover.
• Ahmedabad launched India’s first city-level Heat Action Plan in 2013 after a deadly heatwave in 2010, and the model has since spread to many states and cities.
• Heatwave deaths in India are widely under-recorded because heat is often listed as a contributing factor rather than the direct cause.

What Is a Heatwave in India?

A heatwave in India is a period of unusually high maximum temperature that persists for at least two consecutive days and is declared by the IMD when specific numerical criteria are met. Heat is part of the Indian summer every year, so the definition is built to separate ordinary hot weather from conditions that are dangerous for health.

The difference matters because a place such as Churu in Rajasthan routinely sees 40°C in May, while the same temperature in a hill town would be extraordinary. The IMD therefore treats a heatwave as a departure from local normal as well as an absolute number. Both the plains and the hills have their own thresholds, and coastal areas are treated separately because humidity changes how heat feels.

The word “heatwave” in official Indian usage is also different from the everyday “very hot day”. A single scorching afternoon does not qualify. The IMD requires the condition to be met at a minimum number of stations in a meteorological subdivision for at least two days, and the warning is formally declared on the second day.

How Does the IMD Define a Heatwave?

The IMD defines a heatwave using two tests: a minimum actual maximum temperature and a departure from the normal maximum for that location. The country’s meteorological service applies different numbers to plains, hilly regions and coastal stations.

Plains and hilly regions

• Plains: a heatwave is declared when the maximum temperature is 40°C or more and the departure from normal is 4.5°C to 6.4°C.
• Hilly regions: the actual maximum must be 30°C or more, with the same departure range.
• Severe heatwave: the departure from normal is greater than 6.4°C.

The absolute-temperature route

Where the departure criterion is not met, the IMD uses a second route based on the actual temperature alone. An actual maximum of 45°C or more is classed as a heatwave and 47°C or more as a severe heatwave, regardless of the departure. This route protects very hot regions, where the normal is already high and a large departure is hard to reach.

Coastal stations and warm nights

For coastal stations, a heatwave is considered when the maximum temperature departure is 4.5°C or more and the actual maximum is 37°C or more. The IMD also issues “warm night” and “hot and humid” alerts, because high night-time minimum temperatures and humid air prevent the body from cooling down even when daytime peaks are lower than inland values.

These categories feed the colour-coded warnings that the IMD issues for each district. The system uses green for no action, yellow for being aware, orange for being prepared and red for taking action.

Which Regions and Seasons Are Worst Hit?

The regions worst hit by heatwaves in India are the northwest, the central plains and the east-coast belt, with the season running from March to June. The Indo-Gangetic Plain, central India and parts of the Deccan record the highest number of heatwave days in a typical year.

The core heatwave zone

• Northwest India: Rajasthan, Punjab, Haryana, Delhi and western Uttar Pradesh, where dry continental air from the Thar Desert drives extreme highs.
• Central India: Madhya Pradesh, Vidarbha in Maharashtra and Chhattisgarh, which are far from the sea and warm quickly under clear skies.
• East coast: Odisha, Andhra Pradesh and Telangana, where heat combines with high humidity and so feels worse than the thermometer reading suggests.
• Bihar, Jharkhand and parts of West Bengal: increasingly affected in late spring.

Season and timing

Heatwaves usually begin in March in the south and centre, spread north in April and peak in May and the first half of June. The onset of the southwest monsoon, which normally reaches Kerala around the start of June and then moves north, ends the season. A delayed or weak monsoon extends heatwave conditions, which is why monsoon timing is closely watched by public health officials as well as farmers.

Pre-monsoon heat also builds on dry soils and low cloud cover. Western disturbances, which sometimes bring relief to the north in spring, have been less effective in some recent years, allowing heat to build unchecked.

Why Are Heatwaves in India Becoming Longer and More Frequent?

Heatwaves in India are becoming longer and more frequent mainly because global warming is raising baseline temperatures, and local factors such as land-use change and urban growth add to the effect. The IMD’s long-term records and the assessments of the Intergovernmental Panel on Climate Change (IPCC) both point to a rising number of hot days and warm nights across South Asia.

Main drivers

• Global warming: a hotter atmosphere raises the starting point, so the chance of crossing the 40°C or 45°C marks goes up.
• Changing circulation: weaker western disturbances and persistent high-pressure systems over northwest and central India allow hot, dry air to stay in place.
• Soil moisture loss: dry ground cannot cool the air through evaporation, so more of the sun’s energy turns into sensible heat.
• Land-use change: loss of forests, wetlands and tree cover, together with concrete expansion, reduces natural cooling.
• Aerosols and humidity: air pollution and rising humidity along coasts alter how heat is felt and how fast it builds.

Trends scientists describe

Studies of Indian observations describe a rise in the number of heatwave days and in the length of individual spells over recent decades, along with earlier starts in March and more intense peaks. Climate projections suggest further increases through this century unless emissions fall. Because the Indian summer already pushes against human limits, even a modest additional rise changes the risk sharply.

Humid heat is a particular concern. Researchers use the wet-bulb temperature, which combines heat and humidity, and note that sustained values near 35°C are at the edge of human survivability even for healthy people resting in shade. Parts of the Indo-Gangetic Plain and the east coast are among the regions where humid heat is projected to approach dangerous levels more often.

What Is the Urban Heat Island Effect?

The urban heat island effect is the phenomenon in which a city is warmer than its surrounding countryside because buildings, roads and a lack of vegetation trap and release heat. In Indian cities the difference can be several degrees, and it is largest at night.

Why cities heat up more

• Concrete, asphalt and dark roofs absorb sunlight by day and release it slowly after sunset.
• Narrow streets and tall buildings reduce airflow and trap warm air.
• Heat from air conditioners, vehicles and industry adds to ambient temperatures.
• Loss of trees, lakes and open ground reduces shade and evaporative cooling.

Who is most exposed

Dense low-income settlements are often the hottest parts of a city. Homes with tin or asbestos roofs and little ventilation become ovens in May, and residents may have no fans, cooling or reliable electricity. Outdoor workers such as construction labourers, street vendors, delivery riders, traffic police, farm workers and brick-kiln workers face direct exposure for many hours. Warm nights compound the problem because the body gets no recovery period, so the cumulative strain builds over several days.

What Is the Health and Mortality Toll of Heatwaves in India?

Heatwaves in India cause heat exhaustion, heatstroke, dehydration and deaths, and they worsen existing heart, kidney and respiratory conditions. Official death counts are widely considered to understate the real toll.

Major historical episodes

• The 1998 heatwave is remembered as one of the deadliest in modern Indian records, with deaths running into the thousands.
• The 2010 heatwave in Ahmedabad led directly to the creation of the city’s pioneering Heat Action Plan.
• The 2015 heatwave, concentrated in Andhra Pradesh and Telangana, caused more than two thousand reported deaths nationally.
• Later years, including 2019 and 2022, brought long, early and widespread heat across northern and central India.

Why the numbers are uncertain

Deaths from heat are often recorded as cardiac arrest, stroke or kidney failure, with heat only an underlying trigger. Many deaths happen at home, in rural areas or in the informal sector without postmortem examination. Official figures therefore capture mostly heatstroke cases reported by hospitals, and studies of excess mortality tend to find larger effects than reported counts.

Wider social and economic costs

• Labour productivity: outdoor and factory work slows or stops during peak hours, reducing incomes.
• Agriculture: early heat in March can shrivel wheat grain during its filling stage and cut yields.
• Power demand: peak electricity demand rises as cooling use grows, straining grids and causing outages.
• Water stress: reservoirs fall and drinking water shortages deepen, particularly in cities and dry regions.
• Livestock and wildlife: animals suffer heat stress and water scarcity.

Vulnerable groups include infants, older adults, pregnant women, people with chronic illness and those who are homeless or work outdoors.

How Do Early Warnings Work for Heatwaves in India?

Early warnings for heatwaves in India work through IMD forecasts that are issued days ahead for each district and passed to state disaster management authorities, health departments, media and the public. The IMD supplies an extended-range outlook, a five-day district-level forecast and nowcast alerts for the following hours.

The warning chain

1. The IMD analyses temperature observations, satellite data and model forecasts.
2. District-wise colour-coded alerts are published, with red signalling severe conditions that call for action.
3. State disaster management authorities and district collectors activate their local plans.
4. Health departments alert hospitals, and municipal bodies set up shelters and water points.
5. Messages reach citizens through television, radio, newspapers, SMS and social media.

The challenge is to turn a forecast into behaviour. Warnings are effective only if they reach outdoor workers and vulnerable households and if local bodies have the means to respond, such as drinking water, shade, adjusted work hours and medical readiness.

What Are Heat Action Plans?

Heat Action Plans (HAPs) are local or state plans that set out how authorities will prepare for, respond to and learn from heatwaves, with clear roles for health, water, labour, education and municipal agencies. Ahmedabad launched India’s first one in 2013, after the 2010 heatwave, in partnership with public health researchers and international experts.

Core elements of a Heat Action Plan

• Early warning systems and inter-agency communication.
• Preparedness of hospitals, with cooling wards, rehydration supplies and trained staff.
• Public awareness, including tips on hydration, clothing and avoiding peak-hour exposure.
• Reducing heat exposure through shade, drinking water points, adjusted school and work timings and cool roofs.
• Targeted support for vulnerable and outdoor workers.
• Monitoring and review after each season to improve the plan.

Spread across India

After Ahmedabad’s example, the National Disaster Management Authority (NDMA) issued guidelines for preparing action plans to manage heatwaves, and many states and cities, including Odisha, Andhra Pradesh, Telangana and Maharashtra, adopted their own plans. Coverage has grown over the years, though quality varies. Common criticisms are limited funding, weak coverage of rural and informal-sector workers, and plans that exist on paper but are poorly implemented.

Heatwave is not listed among the nationally notified disasters that qualify for central relief funds in the same manner as floods or cyclones. States often treat it as a state-specific disaster, which affects how much money flows to prevention and compensation.

What Measures Reduce Heat Risk in Practice?

The measures that reduce heat risk combine quick individual precautions with longer-term urban and building design changes. Practical steps work best when combined at household, workplace and city level.

First aid for heatstroke

Heatstroke is a medical emergency in which body temperature rises to dangerous levels and the person may become confused or lose consciousness. First aid involves moving the person to shade, cooling the body with water or wet cloths, giving fluids if they are conscious and getting medical help at once. Cooling quickly is more important than anything else.

Why Does the Heatwave Problem Matter for India’s Future?

The heatwave problem matters because India has a large population exposed to heat, many people who work outdoors and rising cooling demand, so health, productivity, food and energy are all affected at the same time. Adaptation is therefore a development issue as well as a weather one.

India’s strategy blends several tracks. These include stronger early warning, better data on heat deaths, climate-resilient urban planning, passive cooling in housing, efficient and affordable air conditioning, tree cover and protection of workers’ rights during extreme heat. Linking Heat Action Plans to labour rules and health-system funding is widely viewed as the next step. Reducing greenhouse gas emissions globally remains essential to limiting how severe future heatwaves become.

Bottom Line

Heatwaves in India are defined by clear IMD thresholds and are growing in frequency and duration under a warming climate, with cities and outdoor workers bearing much of the risk. Early warnings and Heat Action Plans have shown that deaths can be reduced, but the gains depend on funding, implementation and attention to the most exposed communities.

Frequently Asked Questions

What temperature is a heatwave in India?

The IMD declares a heatwave when the maximum temperature reaches at least 40°C in the plains or 30°C in hilly regions and is 4.5°C or more above normal. It is also declared when the actual maximum reaches 45°C. A severe heatwave is declared when the departure exceeds 6.4°C or the maximum reaches 47°C.

Which months have heatwaves in India?

Heatwaves in India occur mainly from March to June, peaking in May and early June. The season ends when the southwest monsoon spreads north, so a delayed monsoon extends the hot period. In some years, unusually early heat is recorded in March.

Which Indian states are most affected by heatwaves?

Rajasthan, Delhi, Punjab, Haryana, Uttar Pradesh, Madhya Pradesh, Vidarbha, Odisha, Andhra Pradesh and Telangana are among the regions most affected. Northwest and central India record the highest temperatures, while the east coast combines heat with high humidity. Bihar and Jharkhand are also increasingly hit in late spring.

Are heatwaves in India getting worse because of climate change?

Yes, scientific assessments show more heatwave days, longer spells and higher peak temperatures as the climate warms. Local factors such as urban growth, loss of tree cover and dry soils intensify the effect. Projections indicate that risk will continue rising unless global emissions fall.

What is a Heat Action Plan?

A Heat Action Plan is a coordinated plan that tells authorities how to prepare for and respond to heatwaves through early warnings, hospital readiness, public awareness and measures to reduce exposure. Ahmedabad introduced the first city plan in 2013, and many states and cities have followed. The National Disaster Management Authority has issued guidelines to help local bodies prepare them.

How can people protect themselves during a heatwave?

People can protect themselves by drinking water frequently, wearing loose light-coloured cotton clothing and avoiding strenuous work in the afternoon. Staying in shade or a cool room, using oral rehydration solution and checking on older relatives also helps. Anyone with confusion, very high body temperature or fainting needs urgent medical care.

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