Heat Waves: Rising Frequency and Intensity – Explained, pointwise

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The IPCC data show that the atmospheric CO2 concentrations today are higher than at any time in the prior two million years. The temperatures today have exceeded those in the last 6,500 years. Gentler summers have been replaced by intense heat waves. In 2003, Europe experienced 47°C. In 2016, India witnessed 51. 0°C and in 2021, Canada experienced 49. 6°C. In 2022, Antarctica is 40°C hotter than usual. This rising intensity of heat waves causes a significant impact on health, assets and stability of the world. The situation warrants enhanced engagement of communities and nations in order to duly tackle the approaching danger of heat waves. 

The Images depicts the increasing frequency of Heat waves UPSC

Source: The Times of India

What are heat waves?

According to the Indian Meteorological Department (IMD), a Heat wave occurs if the maximum temperature of a station reaches at least 40°C or more for Plains and at least 30°C or more for Hilly regions. There are other criteria as well:

(a) 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 

(b) 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.

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What is the scenario of heat waves in India?

A recent study by the Banaras Hindu University (BHU), in collaboration with the Department of Science and Technology (DST) and the Ministry of Earth Sciences (MoES), has found a spatial shift of heatwaves in India.

The study has found a warming pattern over northwestern and southern India, while a progressive cooling phase over northeastern and southwest regions of the country. 

The study found three prominent heatwave prone regions: Northwestern, Central, and South-central India, with the highest being in west Madhya Pradesh (0.80 events/year). 

The study has also found a significant decrease in heat waves over the eastern region, that is Gangetic West Bengal (−0.13 events/year).

The study has also found severe heatwave events have shown a “southward expansion and a spatial surge during the decades of 2001–2010 and 2010–2016”. The increase in heatwaves in Karnataka and Tamil Nadu are particularly significant and will increase in the future.

What are the reasons behind the increasing frequency of Heat Waves?

Greenhouse Gas Emissions: The primary driver is rising greenhouse gas emissions and the consequent change in the entire climate system. Due to enhanced global warming, scientists expect greater occurrence of heat waves which would have a more significant impact on Arctic and Antarctic ecosystems.

Erratic Nature of Monsoon: Many experts have deduced that rising instances of unusually long dry phases during Monsoons mean that soil moisture drops to a remarkably low level. This reinforces the heat waves.

Urbanization: The urban centres are full of concrete structures that enhance the occurrence of heat waves and create an urban heat island effect. The materials used to build cities like asphalt, concrete, bricks and other supplies are very dense in their composition. Further the darker colors used to paint the buildings also absorb and retain short-wave radiation from the sun.

Similarly, the configuration of buildings in cities also results in heat waves. When big buildings are amassed along a waterway, like in Mumbai and other coastal cities, the wind coming off the waterway can get blocked. Also, when buildings are placed close together, they reduce the convective movement of air which makes it to stagnate and heat.

Demand for Air Conditioning: With a rise in temperature and an enhancement of per capita income of masses, a rise in installation and usage of air conditioners is witnessed in residential and commercial spaces. This provides temporary cooling inside but enhances the outside temperature thereby increasing occurrence of heat waves.

What are the impacts of Heat Waves?

Human Health: The 2015 heat wave caused a massive loss of life in India, around 2,500 deaths by various estimates. Excessive Heat impacts peoples’ quality of life, harms those who suffer from respiratory and cardiovascular conditions and exacerbates asthma in children, affecting their ability to develop in a healthy way.

Economic Loss: An ILO study says that at at 34°C, workers can lose up to 50% of their work capacity. Currently, US$ 41 trillion in GDP is at risk from heat stress globally. By 2030, heat productivity loss could equal 80 million full-time jobs and US$ 2,400 billion, impacting tropical countries like India the most.

Loss of labor productivity would impact agriculture, construction, fisheries, forestry; sectors which are primarily outdoor and demand heavy effort.

Creation of Heat Domes: Some scientists believe that there exists a positive correlation between rising temperatures and creation of heat domes. A Heat Dome is created when an area of high pressure stays over the same area for days or even weeks, trapping very warm air underneath – rather like a lid on a pot. 

When the heat dome phenomenon kicks in – railway tracks buckle, electricity lines melt and roadways crack.

The image depicts the creation of Heat Dome UPSC

Source: AFP

Cascading Extremes: A hot and dry weather extreme causes more evaporation from plants and soil which means a more rapid drying-out of the surface. A dry surface emits more heat and increases temperatures in the atmosphere. So, a heatwave can bring ‘cascading extremes’, triggering the next damaging weather phenomenon like a drought.

Food Security: The rise in heat waves will increase probability of droughts, decrease labor productivity and enhance demand of water in a scenario of decreasing groundwater levels. All this would brutally impact agriculture production and deter food security. 

What are the future projections for India?

Global warming is going to exacerbate the situation.

In India specifically, there is the possibility of amplifying impacts associated with transitional climate zones that change from the aridity of Rajasthan to the more humid east. These zones are very sensitive to climatic changes — these areas go very green in the event of good rain and turn extremely brown when facing dry heat. This would mean greater loss of green cover in the transition zones.

So, India will see an increase in temperature in general and witness a greater intensity due to its peculiar climatic zones.

What should be done?

First, there is a need to acknowledge the fact that heat waves disproportionately impact the poor, diseased and old people. Thus focusing on these groups to ensure that they are getting enough hydration and ventilation can help in reducing the impact of heat waves.

Second, the masses should be encouraged to adopt more energy efficient solutions like using desert coolers in place of air conditioners in dry areas. For this, collaboration with environmental NGOs like Greenpeace can be extremely helpful.

Third, production of energy should be done using clean and renewable resources as the thermal and fossil based production releases a significant amount of greenhouse gasses. Proper implementation of National Solar Mission, National Wind energy policy etc. initiatives are desired for this. 

Fourth, the nations should focus on creating more and more green spaces as they are a panacea for heat waves. The UN noted that investing US$ 100 million in street trees globally can bring 77 million people a 1°C temperature reduction. Restoring Seoul’s Cheonggyecheon stream lowered the temperature by 5.9°C.

Fifth, while renewable energy generation must increase, the nations should also focus on smaller mitigation measures like air vents below roofs, painting surfaces albedo or pale shades and heat-sensitive window placements on buildings.

Sixth, the government should also take proactive steps for the workers who would be facing productivity loss. This involves giving them protective gear to wear in order to lower heat exposure and allowing regular rest and water breaks during the day.


The UNEP data show humans face 220 million more heatwave exposures now than in 1986. The situation is alarming and going to get worse in future. Countries can tackle the menace of heat waves only when they collaborate and cooperate on climate change. The rising frequency and intensity of heat waves is a reminder to the world that proactive and not reactive measures are needed immediately.

Source: The Times of India, The Times of India, The Times of India, The Times of India.

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