Heat waves

2024 APR 20

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


GS 3 > Disaster Management   >   Disaster mitigation 


  • The India Meteorological Department (IMD) has recently issued a warning about the increasing severity and frequency of heat waves, particularly in eastern and southern India, where maximum temperatures are expected to rise significantly in the coming days. This trend underscores the escalating challenges posed by these extreme weather events, emphasizing the urgent need for India to enhance its preparedness and response strategies.


  • 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.
  • According to IMD, a 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

If the above criteria are met at least in two stations in a meteorological sub-division for at least two consecutive days and a heat wave is declared on the second day.

Criteria for describing heat waves for coastal stations:

According to IMD, when the maximum temperature departure is 4.5°C or more from normal, a heat wave may be described, provided the actual maximum temperature is 37 °C or more

Marine heatwave:

  • Marine heat waves 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, sea grass 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.
  • India:
    • According to the latest information available from the India Meteorological Department (IMD), the five warmest years on record for India since 1901 are 2016, 2021, 2009, 2017, and 2010, in descending order. 11 out of 15 warmest years were during the recent 15 years (2007-2021).
Description: https://ilearncana.com/iLearnCana_%40dm!N/kc/ckeditor/kcfinder/upload/images/image-20220324182127-2.jpeg
  • 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 the IPCC special report on global warming of 1.5°C, the increase in global temperatures to within the range of 1.5°C to 2.5°C above pre-industrial levels will intensify the severity of heat waves and other extreme weather events.
  • El Nino:
    • 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. 
    • For example, a strong El Niño event in 2015-16 was associated with significant disruptions to monsoon patterns, contributing to prolonged heat waves in India
  • 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.

The urban heat island (UHI) effect is a phenomenon where urban areas experience higher temperatures than their rural surroundings. This is mainly due to human activities and the concentration of buildings, roads, and other infrastructure that absorb and retain heat. The World Meteorological Organization notes that the UHI can increase temperatures by 5°C to 10°C, intensifying heatwaves in urban settings

Description: Urban heat island | World Meteorological Organization


  • Pollution:
  • Increased greenhouse gases, aerosols, and particulate matter from activities like power generation and transportation enhance heat waves. These pollutants absorb and re-emit infrared radiation, raising atmospheric heat and intensifying the urban heat island effect in densely populated areas.
  • 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.
  • Impact on food production and food security: Heat waves reduce crop yields and disrupt food supply chains, heightening food insecurity.
  • Loss of work hours and reduction in labour productivity:
  • India would lose 5.8% of its working hours due to heat stress, equivalent to 34 million full time jobs (ILO).
  • Also, according to an ILO study, at temperatures of 34°C, workers can lose up to 50% of their work capacity.
  • Social Impact:
    • Called as Silent Disaster:
  • It develops slowly and kills/injures humans and animals.
  • The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke.
  • 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.
  • Resource Strain and Regional Conflicts:
  • May create a resource crunch that escalates tensions over water allocation, exacerbating issues like the Cauvery water disputes between regions due to further strained water resources.
  • Disruption in community infrastructure
    • May create a resource crunch, which leads to riots and a lack of trust in government machinery.


  • Early Warning System and Coordination: Implement systems to alert residents about high and extreme temperatures and enhance preparedness for favorable weather conditions.
  • Training for Healthcare Professionals: Develop training programs for medical and community health staff to manage heat-related illnesses effectively.
  • Public Awareness and Outreach: Use various media to disseminate tips on protecting against heat waves and treating heat-related illnesses.
  • Collaboration with NGOs and Civil Society: Work with these groups to enhance public facilities like bus stands and water delivery systems to better handle heat wave conditions.
  • State Nodal Agency: Designate nodal officers at state or district levels to manage Heat Action Plans.
  • Vulnerability Assessment: Identify vulnerable populations and establish heat-health alert thresholds.
  • City-Level Measures: Analyze factors that cause temperature increases in cities, create heat wave risk maps, identify hot spots, and ensure adherence to building codes.
  • India National Cooling Action Plan: Leverage the India National Cooling Action Plan, which outlines strategies for cooling that can reduce heat effects, especially in urban areas. The plan emphasizes sustainable cooling and low-energy solutions to improve living conditions, particularly in heat-prone regions.
  • Policy and Legislation: Develop policies for heat wave preparedness, including labor laws to regulate working hours and conditions during extreme heat, and ensuring water availability.
  • Research and Data Collection: Enhance research on the local effects of heat waves, improve forecasting models, and create solutions to reduce heat impact. Study the effectiveness of heat action plans and learn from international practices.
  • Supporting Vulnerable Populations: Create programs for groups most affected by heat waves, like the elderly, children, and outdoor workers. Include community cooling centers, subsidized air conditioning for low-income households, and specialized care for high-risk individuals.


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 heat waves? (15 marks , 250 words)