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.