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Heatwave incidents on the rise in India, taking place in new areas: Study

A recent analysis by the Mahamana Center of Excellence in Climate Change Research (MCECCR) at Banaras Hindu University (BHU) in collaboration with the Department of Science and Technology and the Ministry of Earth Sciences has found a spatial variation of heatwaves in India. With this weather phenomenon now happening in new areas of the country.

A heatwave is defined as a prolonged episode of extreme temperatures in an area. In addition to temperature, humidity is an important parameter that is considered to declare heat-related stress.


Link to increase in death rate

The presence of moisture in the environment inhibits the thermoregulatory mechanism of evaporative cooling of the body through the process of sweating, which can lead to heat stress. A 0.5 °C increase in mean summer temperature can increase heat-related mortality by 2.5 to 32%, and increase heatwave duration by 6 to 8 days and result in increased mortality. Is. 78%.

The MCECCR study looked at the India Meteorological Department’s pre-monsoon (March-May) and early summer monsoon (June-July) temperature data, spanning 65 years from 1951-2016, to show that the monthly , Seasonal, Decade and Season can be estimated. Long-term trends in heatwaves in the country. It has found a warming pattern over north-west and southern India, while a progressive cooling phase over the northeastern and south-west regions of the country.

The study has revealed a “spatio-temporal variation” in the occurrence of heatwave events, with a markedly increasing trend over three major heat wave prone regions – northwest, central and south-central India, over west Madhya Pradesh. is the most. 0.80 events/year).

“Heatwaves have traditionally been associated with UP, Bihar, Delhi and northern parts of Madhya Pradesh. For the study, we analyzed daily temperatures over a 0.25 square kilometer grid over the past seven decades. Heatwaves and severe heatwaves are both increasing – and we are finding new places where these events are occurring, especially over the past two decades. We have found heatwaves in southern Madhya Pradesh, Andhra Pradesh, Karnataka and Tamil Nadu, where they would not traditionally occur,” said BHU’s Rajesh Mall, lead author of the study along with scientists Soumya Singh and Nidhi Singh.

Mall said the increase in heatwaves is particularly significant in Karnataka and Tamil Nadu, and points to increased incidence in the future.

Interestingly, the study found a significant reduction in heat waves in the eastern region, that is, Gangetic West Bengal (−0.13 events/year).

Over the past few decades, heat waves have emerged in southern states that have not experienced such events before. Particularly severe heatwave events have shown “southward expansion and an endemic boom during the decades 2001–2010 and 2010–2016”, the study said.

During the period 1961–2010, from March–July, the northwest, northern, central and eastern coastal regions experienced the most heatwave days, with an average of eight heatwave days and 1–3 severe heatwave days during the season . .

Two elements have aggravated the heat wave conditions in the country, rising night time temperatures, which do not allow heat discharge at night, and rising humidity levels.


“An increasing trend of heatwave days and severe heatwave days was observed in the decade 2001–2010 compared to previous decades,” the study said. The east and west coasts, which are currently unaffected by the heatwave, will be severely affected. in future.

The analysis further finds a jump in heat-related deaths, from 5,330 deaths reported during 1978–1999 in extreme cases to 3,054 and 2,248 deaths in 2003 and 2015, respectively.

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