Heat Waves

Heat Waves

Why in news :

  • Last week, the India Meteorological Department (IMD) warned that the maximum temperatures over northwest, west, and central India would be 3­5°C higher than the long-term average.
  • On February 21, the national capital recorded its third hottest February day (33.6°C) in more than five decades.

What is a heatwave?

  • 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 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.

The Indian Meteorological Department (IMD) has given the following criteria for Heat Waves :

  • Heat Wave need not be considered till maximum temperature of a station reaches atleast 40°C for Plains and atleast 30°C for Hilly regions.
  • When 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 7°C or more.
  • When 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.
  • When actual maximum temperature remains 45°C or more irrespective of normal maximum temperature, heat waves should be declared.
  • 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 thereby increasing the number of heat wave casualties.

Health Impacts of Heat Waves :

  • The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke.

The signs and symptoms are as follows:

  • Heat Cramps: Ederna (swelling) and Syncope (Fainting) generally accompanied by fever below 39°C i.e. 102°F.
  • Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.
  • Heat Stoke: Body temperatures of 40°C i.e. 104°F or more along with delirium, seizures or coma. This is a potential fatal condition.

The current heatwave situation of heatwave in India and its causes :

  • Heat waves are expected to become longer and more intense and frequent over the Indian subcontinent.
  • In 2022 itself, the heat waves started early and were more numerous.
  • They also extended further south into peninsular India due to a north-south pressure pattern set up by the La Niña, a world-affecting weather phenomenon in which a band of cool water spreads east-west across the equatorial Pacific Ocean.
  • As we eagerly await the likely birth of an El Niño this year, we have already had a heat wave occur over northwest India.
  • Heat waves tend to be confined to north and northwest India in El Niño years.

How do Heatwaves occur?

  • Heat waves are formed for one of two reasons
    1. warmer air is flowing in from elsewhere or
    2. it is being produced locally.
  • It is a local phenomenon when the air is warmed by higher land surface temperature or because the air sinking down from above is compressed along the way, producing hot air near the surface.

Syllabus : Prelims + Mains; GS1 – Geography

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