Scorching Summers Are Inevitable. Is Delhi HAP-less?

There were 554 such heatwave days in India last summer. The official toll stood at 360 lives lost to the heat. Expert studies put the number closer to 700. 

“The heatwave is such a condition that if precautionary measures are not taken, a person can die,” says Mrutyunjay Mohapatra, the Director-General of Meteorology at the IMD. 

He tells The Secretariat that this year, the IMD predicts an above-normal number of heat wave days for the country.

The predictions till May forecast that most of India — except the northeast, extreme north, and the southwestern and southern parts of peninsular India — will face more heatwave days than usual. 

We’re at a stage where it’s faster to rattle off the places in the country that are not expected to experience heatwaves, than those that will. 

So the burning question isn’t “Will Delhi face a scorching summer this year?” because it will. And so will most parts of India. The pertinent question is “Is Delhi ready for the scorching heat?” 

Delhi HAP(less)

The Heat Action Plan for Delhi is due to be updated for summer 2025, but while summers have begun, the new plan has not been released yet. 

While sources say it won’t be much different from 2024’s plan, there is scope to improve its effectiveness.

Sweltering heat doesn’t necessarily mean a heatwave. 

Defining The Threat

Even if a person feels the cartoonish wavy lines emanating from them 5 minutes after standing in the summer sun, a hot day doesn’t necessarily mean a heatwave. 

A heatwave is when temperatures are much higher than what is normal for a place. Since different areas have different usual temperatures, the level at which a heatwave is declared changes from place to place.

In India, a heatwave is declared when the maximum temperature reaches at least 40°C in plains and 30°C in hilly regions. There are two main criteria for classification.

Based on deviation from normal, a heatwave is declared if the temperature is 4.5°C to 6.4°C above normal, and a severe heatwave if it exceeds 6.4°C above normal. The second method, based on actual temperature, states that a heatwave is declared when the maximum temperature is more than or equal to 45°C, and it is termed severe if it is more than or equal to 47°C. 

For an official heatwave declaration, these conditions must be met in at least two stations within a meteorological sub-division over two consecutive days. The heatwave is then declared on the second day.

Impact 

Mohapatra tells The Secretariat why predicting heatwaves can save lives. “Heatwaves pose significant risks to vulnerable populations, including the elderly, children, and those with pre-existing health conditions, leading to heatstroke, dehydration, and strain on infrastructure. Authorities are crucial in providing cooling centers and issuing timely heat advisories,” he says. 

“The impact based forecast that we issue takes care of the requirements of various sectors. It is provided in a colour-coded message that is green, yellow, orange, red. Yellow means 'be updated on heatwave', orange means 'be prepared to take actions', and red means 'please take actions due to the heatwave',” he explains. 

In addition to that, the IMD prepares an impact matrix. It states the impact on various sectors as per the guidelines prepared by the National Disaster Management Authority. Mohapatra says that, if this matrix is implemented by all sectors, it can reduce not only the loss of lives, but also reduce the loss of infrastructure. 

Time To Evolve Definitions?

Clear and accurate definitions are important because they guide how heatwaves are tracked, when warnings are issued, and how governments respond. 

There is growing debate over whether India’s current definition reflects the dangers of extreme heat. Experts point out that our guideline focuses on temperature, without considering other key factors like humidity, how long the heat lasts, night-time temperatures, or the urban heat island effect. 

Concepts like the heat index combines air temperature and relative humidity. It is how hot the weather actually “feels like” on the skin. Heat discomfort, on the other hand, considers a combination of meteorological factors like temperature, humidity, wind, and sunshine, as well as social factors like clothing, type of work, and place of residence, besides physiological factors like health, co-morbidities, and age. 

That's because not everyone feels the heat in the same way. Consider the experience of a white-collar office-going person with an air conditioned home, work, and car, compared to an informal worker at a brick kiln, who lives in a tin-roofed shelter, works long hours in the heat, and has limited access to drinking water or medical care.

The rule that conditions must be met in two stations for two days may also delay alerts in smaller or more vulnerable areas. As heatwaves become more intense and frequent because of climate change, experts are calling for region-specific, impact-based definitions that better capture how heat affects people on the ground.