Heat Waves

  • Category
    Geography
  • Published
    27th Jun, 2019

In early June 2019, an intense heat wave scorched many parts of India which led to the death of 36 people in the country, mostly from Andhra Pradesh.

Context

In early June 2019, an intense heat wave scorched many parts of India which led to the death of 36 people in the country, mostly from Andhra Pradesh.

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  • In 2019, sparse rainfall during the pre-monsoon season, along with a delayed monsoon, has made the heat more unbearable.
  • The NDMA official added that Churu (Rajasthan), where temperature crossed the 50 degrees Celsius mark, has not registered a single death whereas parts of Andhra Pradesh have witnessed most number of deaths, where the temperature was relatively lower.
  • Reason behind this Anomaly
  • The Comfortable Index of a region increases with the increase in humidity. Comfortable Index measures the human discomfort due to the combined effects of heat and humidity.
  • Since humidity in Andhra Pradesh would be 80-90 per cent, it makes the overall comfortable index much more than a person in the state is used to experiencing. This will make people feel that they are experiencing temperatures above 70°Celsius.

This is true about most coastal states like Odisha, Andhra Pradesh and Telangana whereas Churu has humidity around 10 to 15 per cent.

  • This happens because it is not just temperature, but humidity also plays a
  • Weak El Niño conditions may also play their part in ensuring higher than normal temperature.

Heat Waves

Heat Wave is simply, a continuous spell of abnormally hot weather. Heat wave need not be considered till maximum temperature of a station reaches at least 40º C for Plains and at least 30º C for Hilly regions.

Criteria for declaring Heat Wave followed by IMD

Situation 1 - When normal maximum temperature of a station is less than or equal to 40º C. Declare Heat Wave if:

  • Heat Wave Departure from normal is 5º C to 6º C
  • Severe Heat Wave Departure from normal is 7º C or more

Situation 2 - When normal maximum temperature of a station is more than 40º C. Declare Heat Wave if:

  • Heat Wave Departure from normal is 4º C to 5º C
  • Severe Heat Wave Departure from normal is 6º C or more

Situation 3 - When actual maximum temperature remains 45ºC or more irrespective of normal maximum temperature, heat wave should be declared.

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