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Severe heatwaves are likely to impact parts of northwest, central and peninsular India in next four to five days, while many parts of northeast India will experience very heavy to extremely heavy rainfall during the same period: India Meteorological Department (IMD).

Under the influence of converging strong south-westerly winds from the Bay of Bengal– Northeast India is likely to experience heavy to very heavy rainfall with extremely heavy falls from May 25 to 27.


  • IMD has issued an orange alert in Delhi, Punjab, Haryana, and Chandigarh from May 24 to 27 for heatwave, in west and east Rajasthan for heatwave and severe heatwave; and in Vidarbha for heat wave.
  • An orange alert is issued when a heatwave is likely to persist for more than four days or a severe heatwave for more than two days.
  • There is a high risk of heat-related illnesses such as a heat stroke for people exposed to the sun for prolonged hours or doing heavy work; children, elderly and people with chronic diseases are also vulnerable.
  • The heatwave is likely to affect relief and rehabilitation work related to the coronavirus disease (Covid-19) pandemic that is ongoing in many parts of the country.
  • However, with a lockdown still in effect across India, albeit with considerable relaxation of restrictions, there is not likely to be as much movement of people or vehicles as there might have been otherwise.

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 and South-Central parts of India.
  • Heat Waves typically occur between March and June, and in some rare cases even extend till July. The extreme temperatures and resultant atmospheric conditions adversely affect people living in these regions as they cause physiological stress, sometimes resulting in death.
  • Higher daily peak temperatures and longer, more intense heat waves are becoming increasingly frequent globally due to climate change.

Criteria for Heat Waves

  • The Indian Meteorological Department (IMD) has given the following criteria for Heat Waves:
  • Heat Wave need not be considered till the maximum temperature of a station reaches at least 40°C for Plains and at least 30°C for Hilly regions.
  • 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 and Severe Heat Wave Departure from normal is 7°C or more.
  • When the normal maximum temperature of a station is more than 40°C, Heat Wave Departure from normal is 4°C to 5°C and Severe Heat Wave Departure from normal is 6°C or more.
  • When the actual maximum temperature remains 45°C or more irrespective of normal maximum temperature, heat waves should be declared.

What causes heat waves?

  • All statistics on heat waves listed above refer to trends between March and June, but there’s no evidence that there are more heat waves in March as opposed to April or May.
  • The Indian Ocean temperatures are also rising faster than the other oceans, and this, too, may be reducing moisture over the Indian mainland, thus playing some part in longer stretches of hot days.
  • Deforestation, the heat-island effect, and industrial pollution are also being blamed for exacerbating heat waves.
  • According to the MET Department, the presence of an anti-cyclonic circulation over south Pakistan and neighbouring regions is the reason behind the hot winds prevailing over the entire northwest India.
  • Although Global Warming can be cited as reason, there isn’t enough evidence on the mechanism of how Global Warming could be the cause.

-Source: Hindustan Times

December 2023