Broken Signals: India's Heatwave Warnings Are Missing the Mark

Jun 01, 2025

By Soumya Dutta

In the summer of 2016 in Indore, Kusumlata Devi (name changed), an elderly informal waste worker, was at her usual work of collecting metal and plastics wastes from the top of the garbage dump, items that she sells to the small-scale recyclers to earn a living.

Her half-torn woven polythene bag was less than half full and she was not happy. That day’s collection will not give her enough money. She was feeling a little hot, dizzy and then things went blank.

The next thing she saw was the ragtag bed she was lying on in her jhuggi (informal settlement), surrounded by family members. Once she recovered a little, she was told that she passed out, probably out of heat exhaustion, and was rescued and carried back by fellow (informal) waste workers.  Her life was saved that day by quick action of fellow workers, with no assistance from the system.

In the summer of 2023, which broke all previous records of being the hottest year on instrumental record (till that was broken in 2024), Manjar Alam (name changed) was working as a mason in a building site in Delhi. It was a very hot and humid day, and he had not received any information of a heatwave declaration. This is per usual, because heat and other climate warnings barely, if ever reach workers.

As he felt unwell working in this oppressive heat, he came home early and asked his wife for food.  As he sat down to eat, he fell flat, never to get up again.

His was another life lost to the fast-rising heat impact, to become another number to the statistics.

Both these examples are an illustration to the fact that while urban poor and informal workers are the populations most at risk for adverse impacts of heat such as heat stress, exhaustion or heat stroke, the Indian Meteorological Department’s readings fail to accurately assess their risk for health impact and their warnings fail to reach them.

These stories ask us the question; how do we centre the needs of the most vulnerable while designing an effective disaster warning system?

The Rising Threat to Humanity

In the 21^st century, the ‘Climate crisis’ has become one of the biggest challenges facing humanity, with no ‘relief’ in sight which has led to the sharp increase in temperatures and the threat levels to all vulnerable communities globally.

With the weak climate pledges from governments, the global annual mean temperature is set to rise about 2.9 C above pre-industrial era by the end of the century. The year 2024 was about 1.58 C warmer than the pre-industrial average temperature (which was the average global annual mean temperature of the years between 1850-1900). Sadly, despite facing an advancing climate catastrophe, the global Greenhouse Gas emissions have kept rising even after the over-hyped Paris Climate Change Agreement (PA) of 2015.

The Indian Subcontinent is Burning Up

The Indian subcontinent has been particularly affected by the rise in global temperature due to its proximity to the equator. Though records show a less-than-global-average temperature-rise over the Indian landmass as a whole, the days when both maximum temperature and max relative humidity spikes, are on the rise.

There are both direct and indirect impacts of heat and humidity. The direct impacts of heat on India currently includes – significant crop losses which contribute to malnutrition (and even stunting in children), power shortages which also affect the manufacturing sector and increased water scarcity all of which impacts the economy and leads to significant GDP loss.

Furthermore, heat is also causing indirect climate related impacts in the oceans surrounding India.

A comprehensive assessment of climate change impacts and trends over the Indian region, by India’s Ministry of Earth Sciences published in 2020, shows a scary scenario. The projection shows that in the coming decades both extreme precipitation and extreme heat incidents will worsen. This report also showed how coastal cities and towns are now facing more frequent and more intense tropical storms and cyclones, driven by higher sea surface temperatures in both the Bay of Bengal and the Arabian Sea which only stands to worsen.

Vulnerable Populations

A quick look at the temperature map of India above reveals that due to its geography, the areas most affected by heat appear to be located in the North-West regions and Indo Gangetic plain. This is also the area where there is a higher population density and higher prevalence of poverty, both of which adversely affect the ability of the people to effectively deal with and recover from heat.

And when the average temperatures become high, urban areas suffer from even higher temperatures, not least because of the Urban Heat-Island (UHI) Effect, which keeps congested areas temperatures about 4 to 6 C higher than surrounding open areas.

Further it is important to note that heat and its impacts are disproportionate. Statistics say that the urban poor and informal work sector consisting of people who do demanding physical work such as construction workers, rickshaw pullers, farm workers, domestic helps, sanitation workers, street vendors etc are affected more by the heat. (Nivarana published a story by Sanskar Gupta on the impact of heat on unorganised settlements in Bhopal here)

After exhausting days working in extreme heat, many labourers return to cramped, poorly ventilated homes that offer no relief—only more heat and humidity. With no formal plans or advisories to address indoor heat stress, the health risks quietly intensify over time.

Though the Government of India does not keep a regular heat impact related death record, some studies have shown that well over 24,000 deaths took place between 1992 and 2015, with ‘Heatwatch’ recording 733 heat deaths in 2024.

These numbers and figures reveal that there are vulnerable populations in India who are adversely impacted by heat who might benefit from receiving appropriate alerts about possible heatwaves. However, we need to critically examine whether the current system of heatwave alerts accurately represents the ground data on temperature and whether they appropriately reach the correct populations.

Heat Metrics of Relevance

In India, the India Meteorology Department IMD determines and announces if and when a heatwave condition has started in any place and time. The IMD determines heatwaves by using either a temperature cut off for the maximum temperature recorded in a day or for how hotter is the maximum temperature compared to the normal temperature of that area.

IMD Criteria for Declaring Heatwaves in India

 

Condition	Criteria Met
Departure from Normal	Maximum temperature is ≥ 4.5°C above normal andactual maximum temperature is ≥ 37°C.
Heatwave	Maximum temperature reaches or exceeds:– 40°C for plains– 30°C for hills– 37°C for coastal areas.
Severe Heatwave	Either: – Departure from normal is ≥ 6.5°C (significantly above normal) OR– Actual maximum temperature is ≥ 45°C.

It also uses a metric known as ‘Heatwave Days’, this is defined as the number of days in a particular location where the maximum recorded temperature has crossed the threshold for declaring a heatwave.

In March 2025, the India Meteorological Department IMD said that the number of heatwave days might double this year as compared to 2024, which was already a bad year with a record breaking 554 heatwave days. This rising trend is visible already.

Another heat metric of importance is the heat index.

Heat index which is also known as the apparent temperature combines the metrics of measured temperature with the humidity in a location. This indicates what the heat feels like to a human body. Because the human body when exposed to heat cools itself by sweating and humidity in an area reduces that capacity – a more humid area will have a higher heat index which will then indicate that more harm to the human body is possible.

Gaps in The Current Heatwave Warning System

Given the background of the harmful impacts of heat and the populations it affects, there are three clear reasons why the present IMD heat warning system is inadequate

Firstly, the Indian Meteorological Department (IMD) weather monitoring stations are often few and widely spaced, and they are typically located in cooler, shaded, or less densely populated areas—such as airports or research campuses. However, the environmental conditions experienced by working-class people—who are usually outdoors or in poorly ventilated, crowded areas—are significantly different and often far more severe. Due to the Urban Heat Island (UHI) effect, where built-up city areas retain more heat, and higher exposure to air pollution and humidity, the actual “felt” temperature in these localities can be much higher.

As a result, IMD stations may underreport the true heat stress conditions in urban centres. For example, the IMD station in Guwahati is located at the city’s airport, approximately 25–30 km away from the densely populated city centre. This station is situated in a relatively open, green, and less congested area. Consequently, the temperatures it records are unlikely to reflect the real conditions in the heart of Guwahati, where overcrowding, inadequate infrastructure, and trapped heat exacerbate the thermal burden on residents.

Heat-related health impacts are highly context-dependent—they depend not just on ambient air temperature, but also on humidity, air quality, crowding, access to shade, water, and ventilation. Relying solely on IMD station data may mask the intensity of exposure faced by vulnerable populations, leading to delays in issuing heatwave alerts and insufficient public health responses.

The standard temperature recorded by IMD and other weather agencies—known as the 2-meter air temperature—is taken in shaded, ventilated conditions about two meters above the ground. While useful for consistency, it often grossly underestimates the actual heat experienced by people working at or near ground level.

Surfaces like asphalt, tin roofs, and concrete structures can become significantly hotter under direct sunlight, often reaching 50–65°C even when the 2-meter air temperature reads 38–40°C.

This disparity is especially dangerous for informal workers such as construction laborers, street vendors, and waste pickers who operate directly in these environments. By relying on cooler, shaded air temperatures rather than real surface heat exposure, official heat warnings fail to reflect the true risk on the ground—putting the most vulnerable populations at even greater peril.

The second critical issue is the underuse of the Heat Index—a far more accurate predictor of heat-related health risks than temperature alone.

While the IMD often shares relative humidity and a “feels like” temperature, it stops short of issuing formal Heat Index warnings that factor in both temperature and humidity.

This is a dangerous gap, especially in tropical and coastal regions where high humidity prevents sweat from evaporating efficiently, crippling the body’s ability to cool itself.

At extreme levels of humidity, this can lead to Wet Bulb Temperatures of 35°C or more—a threshold beyond which even healthy individuals can suffer heat stroke or die within hours. These conditions are no longer rare; climate models predict they will become increasingly common. Yet it is a blind spot in the warning systems that continues to go unaddressed.

Moreover, these alerts, available on smartphones and in the English language, cannot be comprehended by most of the informal workers who need to be the primary targets of such an alert. This exclusion also requires better measures to reach the workers such as, automated phone calls which give the information in the local language and non-technology centred ways of announcements.

And finally, the advisories that the government issues when IMD announces a heat-wave condition, is inadequate to deal with the problems.

The suggestion to not go out is impractical as most workers live on a daily wage basis which places them in severe economic stress. A better option would be to compensate them for the loss of working days due to heat impact.

In high temperature and high humidity conditions, the common advice to “drink plenty of water” is dangerously inadequate. When humidity is high, the body’s primary cooling mechanism—evaporation of sweat—becomes ineffective, meaning internal temperatures can rise rapidly even if one is well-hydrated.

These conditions place immense strain on the heart and kidneys, and if someone begins to suffer heat stress or heatstroke, what they urgently need is external cooling, not just fluids.

Saving lives in such scenarios requires physical infrastructure—such as well-ventilated emergency cooling rooms or shelters with fans, misting systems, or air-conditioning—especially in densely populated, high-risk areas like slums, construction sites, and markets. Yet most Indian cities lack such life-saving measures in their Heat Action Plans, leaving millions dangerously exposed.

Rethinking Heat Alert and Warning Systems

As India is facing longer, hotter, and more dangerous summers, yet its current heat warning system is plagued by critical blind spots that fail to protect vulnerable populations like Kusumlata and Manjar.

To save lives, the warning system must be fundamentally reimagined.

This includes installing a dense network of temperature and humidity sensors in urban slums and other high-risk areas and using real-time Heat Index and Wet Bulb temperature readings to assess actual danger rather than relying solely on raw temperature data.

Alerts must be communicated in local languages through accessible channels such as voice messages, FM radio, and community volunteers.

Crucially, economic safeguards like heat allowances or wage compensation should support workers who cannot safely work during extreme heat. Additionally, investment in cooling infrastructure—such as emergency cooling centers in densely populated low-income neighborhoods—is urgently needed.

As climate change intensifies, heatwaves are no longer minor weather events but slow-motion mass-casualty disasters. Without evolving our warning and response systems, lives will be lost not because the danger was unseen, but because we refused to recognize it where it truly matters.

This article was published by Nivarana: India’s Public Health Plaform (www.nivarana.org) on May 21, 2025 and is republished here with permission. It is edited by Christianez Ratna Kiruba. 

Soumya Dutta is a people’s science activist leader who is extensively engaged with a range of climate, change and ecological issues.