Prepare for the next challenge- Heat waves

GS 3 – Disaster and Disaster Management

Source : The Hindustan Times dated 17/05/2021

Reference :

Context :  An earlier advisory in March 2021 warned that “above normal seasonal maximum temperatures are likely” over most of the country. Over the past decades, such high temperature extremes have become more prevalent.

What is a heat wave?

  • A Heat Wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western parts of India.
  • Heat Waves typically occur between March and June, and in some rare cases even extend till July.

Heat wave distribution in India


According to Indian Meteorological Department (IMD), heat wave is considered if maximum temperature of a station reaches at least 40°C or more for Plains, 37°C or more for coastal stations and at least 30°C or more for Hilly regions.

Following criteria are used to declare heat wave: o

Based on Departure from Normal

  • Heat Wave: Departure from normal is 4.5°C to 6.4°C
  • Severe Heat Wave: Departure from normal is >6.4°C
  • Based on Actual Maximum Temperature (for plains only)
  • Heat Wave: When actual maximum temperature ≥ 45°C
  • Severe Heat Wave: When actual maximum temperature ≥47°C
  • To declare heat wave, the above criteria should be met at least in 2 stations in a Meteorological sub-division for at least two consecutive days and it will be declared on the second day.


  1. Climate change
    • (MoES) published India’s first national climate change report, Assessment Of Climate Change Over The Indian Region. The report said India’s average temperature had risen by 0.7 degrees Celsius from 1901-2018.
    • India is very susceptible to climate change impacts when it comes to heat because the country’s baseline temperatures are already very high.
    • Humidity is an important part of this equation. For example, the 2015 deaths in Andhra Pradesh and Telangana were due to high temperature and high humidity. This is reflected in the heat index (HI), a measure of how hot it feels when relative humidity is factored into the air temperature.
  2. Urban heat traps.
    • According to the 2018 UN World Urbanization Prospects report, 20% of India’s population lived in cities in 1950. By 2018, that figure had increased to 34%, with 461 million urban dwellers. The country is forecast to add a further 416 million urban dwellers by 2050.

This might lead to the Urban Heat Island effect

  • This affects the poor the most because
    • Higher-income neighbourhoods possess favourable conditions like shading from trees and open green spaces, which reduces the chances of heat getting stored over the day and turning nights warmer.
    •  On the other hand, low-income neighbourhoods are densely-built, which means greater heat exposure and greater amounts of stored-up heat.
    •  A typical house in an informal neighbourhood in Delhi could be 8 degrees Celsius hotter than the outside temperature at night.
    • Also,according to The Natural Resources Defense Council, nine out of 10 homes in India do not have air-conditioning.


Health Impacts of Heat Waves
  • Heat Cramps: Ederna (swelling) and Syncope (Fainting) generally accompanied by fever below 39°C i.e.102°F.
  • Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.
  • Heat Stroke: Body temperatures of 40°C i.e. 104°F or more along with delirium, seizures or coma. This is a potential fatal condition.

Economic impacts

A McKinsey Institute paper says that by 2050, 500-700 billion people in India, Pakistan and Bangladesh could be living in regions which would have a 20% probability of lethal heatwaves every year – could see a hit to their GDP to the tune of 13%.
The International Labour Organization (ILO), in its 2019 report Working On A Warm Planet, says India is projected to lose the equivalent of 34 million full-time jobs in 2030 due to heat stress, with agriculture and construction being the worst-hit sectors.

NDMA guidelines
  • Heat Waves has not been notified as a Disaster as defined under the Disaster Management Act, 2005 by the Government yet.
  • Heat wave is not even notified in the list of 12 disasters eligible for relief under National/ State Disaster Response Fund norms.
  • Hence the National Disaster Management Authority (NDMA) has released National Guidelines for Preparation of Action Plan – Prevention and Management of Heat Wave.
    • Establish Early Warning System and Inter-Agency Coordination to alert residents on predicted high and extreme temperatures.
    • Capacity building / training programme for health care professionals at local level to recognize and respond to heat-related illnesses, particularly during extreme heat events.
    • Public Awareness and community outreach
    • Collaboration with non government and civil society
Way forward

Measures to combat Urban Heat Island effect

  • Cool Roofs
    • Painted with solar reflective paint, covered in white tiles, or with white membrane
    • can help keep indoor temperatures 2 to 5°C lower than households with traditional roofs.
    • need limited maintenance, can save 20% in energy costs.

Case study : Hyderabad has already installed 20,000 square feet of cool roofs and has included cool roofs as one of its corporate social responsibility tools.

  • Green buildings
    • The higher albedo of the plants reflect more of the sun’s energy
    • As the plants transpire, the surrounding ambient temperature of the building is lowered through evaporative cooling. Eg : Rajiv Gandhi International Airport, Hyderabad

Use the heat maps for cities– for better planning
Can help in detecting hotspots.

Case study of Bengaluru city

Stick to climate goals

  •  In a climate change scenario where the world heats up by 3-4 degrees Celsius above pre-industrial levels by 2100, the number of days with dangerous, constant heat could rise to between 100-250.
  • Hence India should take the lead in achieving the targets under Paris Climate Agreements(to reduce carbon emissions by 33 to 35% as intensity of the GDP from 2005 levels)


There’s no single magic bullet that will solve the issue of heat waves in India. Instead it comes down to accumulating small gains from individual steps.
Formulating a Heat Action Plan(HAP) for every city will be a small but significant step in this direction.

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