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. When actual maximum temperature remains 45ºC or more irrespective of normal maximum temperature, heat wave is declared.
The Ministry of Earth Sciences in a report to Rajya Sabha last month has stated that in 2018, the country’s annual mean surface air temperature averaged +0.39°C above the average for the 1981-2010 period. The year 2018 has been recorded sixth warmest since nation-wide records began to be maintained in 1901.
During ‘not so usual’ hot episodes, mortality rate from different causes tend to rise significantly wherein the elders of the society are at a greater risk.
The Ministry has further stated that in comparison to previous three decades, the maximum number of deaths due to heat wave conditions were registered in the 15-year period from 2001 to 2015.
The Ministry in its report to the Rajya Sabha has also said that the average temperature across India during 2018 was much above normal.
The heat wave years like 1971, 1987, 1997, 2001, 2002, 2013 and 2015 witnessed tremendous rise in human deaths.
As per the latest study, heat wave episodes have risen over many parts of the country. The Ministry stated that during hot weather season, stations from the North, North-west, Central, East India and North-East Peninsula, famously known as the Core Hot Zone (CHZ) are more prone to severe heat wave days wherein the frequency is at its peak during May. In India, the heat wave conditions are usually observed from March to July, wherein April to June is the most prone.
States like Punjab, Himachal Pradesh, Uttarakhand, Delhi, Haryana, Rajasthan, Uttar Pradesh, Gujarat, Madhya Pradesh, Chhattisgarh, Bihar, Jharkhand, West Bengal, Odisha and Telangana and Met subdivisions of Marathwada, Vidarbha, Madhya Maharashtra and coastal Andhra Pradesh, all come under Core Hot Zone.
Image Credit: University of Oxford
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