Heat waves

2022 MAR 24

Mains   > Disaster Management   >   Disaster mitigation   >   Disaster Management Act, 2005


  • Parts of north India have been reporting heat waves.


  • A heat wave occurs in a region when abnormally high temperatures are recorded over a long period of time.
  • The World Meteorological Organization (WMO) has not adopted yet a standard and mathematically rigorous definition for heat waves.
  • In India, Heat wave is considered if maximum temperature of a station reaches at least 400C or more for Plains and at least 300C or more for Hilly regions.
    • (a) Based on Departure from Normal
      • Heat Wave                  : Departure from normal is 4.50C to 6.40C
      • Severe Heat Wave      : Departure from normal is >6.40C
    • (b) Based on Actual Maximum Temperature
      • Heat Wave                  : When actual maximum temperature ≥ 450C
      • Severe Heat Wave      : When actual maximum temperature ≥470C

Marine heatwave:

  • Marine heatwaves are periods of extremely high temperatures in the ocean.
  • MHWs have been observed in all major ocean basins over the recent decade.
  • These events are linked to coral bleaching, seagrass destruction, and loss of kelp forests, affecting the fisheries sector adversely.



  • Globally:
    • Since the 1980s, each decade has been warmer than the previous one. The warmest seven years have all been since 2015; the top three being 2016, 2019 and 2020.
    • World Meteorological Organization (WMO) statements suggests that Heat-waves are projected to increase in number, intensity and duration over the most land area in the 21st century.
    • IPCC 6th Assessment report states that every additional 0.5°C of global warming causes clearly discernible increases in the intensity and frequency of hot extremes including heatwaves.
  • India:
    • The five warmest years on record in India are 2016, 2009, 2017, 2010, and 2021. 11 out of 15 warmest years were during the recent 15 years (2007-2021).
    • Heat waves typically occur between March and June, and in some rare cases even extend till July.
    • Many places in the northwest and cities along the southeastern coast report up to eight heatwave days per season. However, the regions in the extreme north, northeast and southwestern India are lesser prone to heatwaves.


  • Climate Change:
    • Climate change is driving global temperature higher and increasing the frequency and severity of heat waves.
    • According to IPCC special report >> global warming of 1.5C- 2.50C will worsen the situation.
  • El Nino and La Nina:
    • El Niño years are associated with a delay in the onset of the Indian Summer Monsoon. Because most heat waves in India occur during the pre-monsoon season, heat waves during El Niño years are longer and hotter.
  • Shifting jet streams:
    • According to a recent study, the polar jet stream is shifting north as global temperatures rise. This would wreak havoc on weather in the northern hemisphere, bringing more extreme events like droughts and heat waves to southern Europe and the eastern US.
  • Hot local winds like Loo:
    • Loo is a hot wind that originates in the desert regions of Iran, Pakistan and Thar Desert and blows eastwards into the Indian plain region in the months of May and June, usually in the afternoons.
    • Its temperature invariably ranges between 45°C and 50°C and causes severe heat waves in the plain region.
  • Anthropogenic causes:
    • Deforestation and increased constructed area:
      • Reduced level of evapotranspiration due to rise of concrete jungles and urban sprawls >> leads to Urban Heat Islands effect.
    • Pollution:
      • High pollution levels and high concentration of GHGs like CO2 (thermal power plants and vehicles) >> GHGs, aerosols, particulate matter are good at absorbing outgoing infrared radiation (long wave radiation).
    • Landscape alterations:
      • Land use change, widespread installation of air conditioning, degraded agriculture practices create urban heat islands.


  • Ecological:
    • Increase the risk of disasters:
      • Exacerbates already existing risks disasters like droughts and forest fires.
    • Loss of biodiversity:
      • Heat waves increases the risk of loss of wildlife habitat and loss of biodiversity.
  • Economic:
    • GDP loss:
      • Heat waves resulted in a total of nearly USD 60 billion in damage globally in 2018.
    • Threat to agricultural and allied sector:
      • Combined heat waves and drought can lead soil to dry out and cause severe harvest failures.
      • Heat waves also led to deaths of poultry, cattle etc.
    • Loss of work hours:
      • India would lose 5.8% of its working hours due to heat stress, equivalent to 34 million full time jobs (ILO).
  • Social Impact:
    • Called as Silent Disaster:
      • It develops slowly and kills/injures humans and animals.
    • Increased mortality:
      • 24,000 deaths between from 1992-2015 (NDMA report)
      • However due to efforts from various stakeholders mortality due to heat waves reduced from 2040 in 2015 to 25 in 2018
    • Reduced productivity:
      • Due to physiological stress, sometimes leading to illness & death.
    • Affects public order:
      • May create resource crunch >> leads to riots and lack of trusts in government machinery
    • Disruption in community infrastructure
      • For ex: Power supply, Public transport, etc.


  • Establish Early Warning System and Inter-Agency Coordination
    • To alert residents on predicted high and extreme temperatures.
    • Early warning systems can also enhance the preparedness of decision-makers and their readiness to harness favorable weather conditions.
  • Capacity building or training programme:
    • For health care professionals at local level to recognize and respond to heat-related illnesses, particularly during extreme heat events.
    • These training programmes should focus on medical officers, paramedical staff and community health staff so that they can effectively prevent and manage heat-related medical issues to reduce mortality and morbidity.
  • Public awareness and community outreach
    • Disseminating public awareness messages on how to protect against the extreme heat-wave through print, electronic and social media and Information, Education and Communication (IEC) materials such as pamphlets, posters and advertisements and Television Commercials (TVCs) on Do’s and Don’ts and treatment measures for heat related illnesses.
  • Collaboration with non-government and civil society:
    • Collaboration with NGOs and civil society organizations to improve bus stands, building temporary shelters, wherever necessary, improved water delivery systems in public areas and other innovative measures to tackle Heat wave conditions.
  • Appointing a State nodal agency and officer:
    • The State should appoint a nodal officer at State or district levels to oversee Heat Action Plan
  • Vulnerability assessment and establishing heat-health threshold temperatures:
    • It is important to identify vulnerable areas and populations in order to establish priorities and minimum thresholds for heat alert and activities  
  • City level measures
    • Identification of factors leading to disproportionate increase in temperature within city
    • Generating a heat wave risk and vulnerability map
    • Mapping hot-spots within city
    • Adhering to building codes in the city


  • Heat wave Action Plan of Ahmedabad:
    • Ahmedabad was among the first city to prepare Heat wave Action Plan.
    • This plan provides a framework for other Indian cities to emulate and help protect their citizens from the extreme heat.
    • The key lesson learnt from Ahmedabad Heat Wave Action Plan:
      • Recognize Heat Wave as a major Health Risk.
      • Map out the 'High Risk' Communities.
      • Setting up of 'Public Cooling Places'.
      • Issue Heat wave alerts through different media.


Q. Explain the factors contributing to the increasing frequency and intensity of heat waves in India. What measures can be taken to reduce the risk of heatwaves?