• What is it?: A heat wave is a period of abnormally high temperatures that occurs during the summer season in India
• Fact: Not included in the notified disasters covered by the Disaster Management (DM) Act of 2005
• Criteria for Defining Heatwaves
  • Physiography of the Region
    • In Plains at least 40°C or more.
    • In Hilly Regions at least 30°C or more.
    • In Coastal Areas, 37°C or more
  • Based on the Departure from Normal Maximum Temperature
    • When the normal maximum temperature of a station is less than or equal to 40°C:
      • Heat Wave: Departure from normal is 5°C to 6°C
      • Severe Heat Wave: Departure from normal is above 7°C.
    • When the normal maximum temperature of a station is more than 40°C:
      • Heat Wave: Departure from normal is 4°C to 5°C
      • Severe Heat Wave: Departure from normal is 6°C or more
  • Based on Actual Maximum Temperature
    • When the actual maximum temperature is above 45°C (Severe Heat Wave at above 47°C)
• Causes of Heatwaves
  • Prevalence of Hot and Dry Air
  • Absence of Moisture
  • Cloudless Skies
  • Large  Anticyclonic Flow
  • Climate Change

Source: Down To Earth