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Heat Wave

Topics Covered:

  1. Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc., geographical features and their location- changes in critical geographical features.
  2. Disaster and disaster management.


Heat Wave


What to study?

  • Static Part: What are heat waves and how are they classified?
  • Dynamic and Current: Why is India vulnerable, effects of heatwaves on health, environment and economy, how should India be prepared?

Context: The Lancet Countdown 2018 report has asked the Indian policy makers to take a series of initiatives to mitigate the increased risks to health, and the loss of labour hours due to a surge in exposure to heatwave events in the country over the 2012-2016 period.

Why is India vulnerable?

  • From 2014-2017, the average length of heatwaves in India ranged from 3-4 days compared to the global average of 0.8-1.8 days, and Indians were exposed to almost 60 million heatwave exposure events in 2016, a jump of about 40 million from 2012.
  • A recent report has placed India amongst the countries who most experience high social and economic costs from climate change. Overall, across sectors India lost almost 75,000 million hours of labour in 2017, from about 43,000 million hours in 2000.
  • The agriculture sector was more vulnerable compared to the industrial and service sectors because workers there were more likely to be exposed to heat.
  • The India Meteorological Department had reported that from 1901 to 2007, there was an increase of more than 0.5°C in mean temperature, with considerable geographic variation, and climate forecasts by research groups project a 2.2-5.5°C rise in temperatures in northern, central and western India by the end of the 21st century.

Important recommendations (Lancet Study):

Identify “heat hot-spots” through appropriate tracking of meteorological data.

Promote “timely development and implementation of local Heat Action Plans with strategic inter-agency co-ordination and a response which targets the most vulnerable groups.”

Review existing occupational health standards, labour laws and sectoral regulations for worker safety in relation to climatic conditions.

What is a Heat Wave?


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:

  1. 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.


  1. 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.


Higher daily peak temperatures and longer, more intense heat waves are becomingly increasingly frequent globally due to climate change.

India too is feeling the impact of climate change in terms of increased instances of heat waves which are more intense in nature with each passing year, and have a devastating impact on human health.

  • Health Impacts of Heat Waves: The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke.
  • Children, the elderly and those with pre-existing morbidities are particularly vulnerable.

Sources: the Hindu.

Mains Question: What is heat wave? Why is India experiencing more heat waves? Also examine what strategy is being followed by states to address the consequences of heat waves.