What are Heat Waves? A Detailed Description

Have you found yourself wiping sweat from your brow a bit too often? Is the fan not enough for you to cool down? India’s blistering heat wave is to blame for that; however, what are heat waves in the first place?

Joginder Sharma, a farmer in Rajasthan, used to wake up every morning before starting his work on the field. The heat wasn’t a problem as he would finish his duties by the late evening.

But this year, the blistering heat was too much for Joginder. Not only was his productivity on the field halved, the farmer faced other issues as well: frequent power outages, stunted vegetables, and occasional heat strokes.

This year, many North and Central India states saw mercuries pushing past the 45 degree mark in a frizzling heatwave that has shortened spring seasons, altered school timings, dried up rivers, perpetual electricity cuts, and tragic deaths.

Between 1970 to 2019, close to 20,000 individuals died due to heat waves. Uttarakhand, Andhra Pradesh and Rajasthan, were the states with the highest number of heat wave days. As the years go on, the number of states affected by heat waves have increased too.

What is a heatwave?

Whenever there is a high-pressure zone that persists over the same place over the course of days or weeks, the air is trapped underneath it. This creates a ‘heat dome’. If the trapped air inside the heat dome surpasses 40°C it is usually considered to be called a heat wave. This temperature onwards is considered harmful to the human body, according to India Meteorological Department (IMD)

The temperature needed to be labelled a heat wave depends on the nature of the region. For it to be considered a heatwave, it should be 37°C along coastal areas, 35°C for hilly areas and 40°C in plain areas.

Heat Islands

A satellite image shared by NASA’s Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station instrument recently showcased how Delhi was significantly hotter than its surrounding rural areas.

In this image, Delhi had a huge red patch, compared to smaller red patches in cities neighbouring the UT such as Sonipat and Panipat. These red patches indicated that the region had high temperatures, or ‘heat islands’.

Just like how a heat wave is created, when a specific area in a metropolitan region is warmer than 2°C compared to its suburban or rural areas, then an urban heat island is formed.

The science behind the formation of heat island effect is due to changes in land surface, waste heat due to energy use, and places where dense vegetation is replaced by concrete for building necessary structures such as roads and buildings.

The sun’s heat is absorbed by concrete and asphalt, raising the land surface temperature. Eliminating vegetation for construction work is detrimental as they serve as natural ‘cooling’ effects to the natural surrounding areas. Hot air is confined in the spaces of skyscraper-tall structures and narrow lanes, reducing air flow. Heat is added into the air with the waste excreted from vehicles, ACs and factors.

Cities like Delhi, Sonipat, Panipat, Jaipur, Kolkata, Chennai, and Trivandrum are mostly at risk of having higher heat island formation in the day.

Adverse Effects of Heatwaves

Physical Impacts

A study in Nature Communications also mentioned that the heat exposure from India’s deathly heat waves shrink more than 100 billion hours of labour productivity, meaning $600 billion of labour work is lost. Reduced labour productivity will have negative trickle down effects to important industries that help drive economic growth.

Mental Impacts

People suffering from mental illnesses are more than three times likely to die because of heatwaves. The heat exposure can lead to ‘heat stress’, which can also lead to mental health disorders such as depression or post-traumatic stress disorder (PTSD). It can aggravate mood disorders and anxiety too.

Environmental Impacts

India’s hospitals and metro stations have seen frequent power cuts due to increased demands for electricity. Swift melting of glaciers leaves more than seven million people, including locals and tourists, vulnerable to the risk of flooding. With falling water supplies, farmers across the country are trying to use it economically. Himachal Pradesh has seen a consistent decline in snow cover since 2020.

Biodiversity and Agriculture Impacts

The heatwave has had disastrous impacts on biodiversity and agriculture: from shrivelling necessary vegetables during the growing season; increasing the frequency of fires in jungles, hospitals and buildings; wiping out the supply of apples; and the premature deaths of baby birds in Punjab.

What can we do about it?

There can be some measures we can use.

Installing warning systems that can detect heatwaves and advise the general population of combative measures can be useful. In addition, print and social media can help spread resource material on heat-proof shelter facilities and public areas that have easy access to clean drinking water. There also needs to be an increase in afforestation, which can improve natural cooling effects of urban and rural regions.


  1. https://www.who.int/india/heat-waves

  2. https://www.c2es.org/content/heat-waves-and-climate-change/