Behind heat surge, factors that will only worsen | Latest News India - Hindustan Times
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Behind heat surge, factors that will only worsen

ByJayashree Nandi, New Delhi
May 30, 2024 04:54 PM IST

This unprecedented heat is an accepted trend among climate scientists and is expected to worsen in coming years

Near 50°C temperatures have become increasingly common across India in recent years. While a few stations in Rajasthan, such as Phalodi or Churu, have always recorded such extreme heat, stations in Haryana, Delhi, Madhya Pradesh, Bihar, Uttar Pradesh, and Punjab are now also reaching or even surpassing 50°C for a day or two. On Monday, several areas in these states also experienced warm nights, with night-time temperatures at least 5°C above normal. Similar conditions prevailed on Tuesday.

A worker sprinkles water on a subway to bring relief from the heat in Delhi. (AFP)
A worker sprinkles water on a subway to bring relief from the heat in Delhi. (AFP)

This unprecedented heat is an accepted trend among climate scientists and is expected to worsen in coming years. The frequency and intensity of heat waves in India have increased significantly from 1951-2015, with accelerated warming in the last 30 years. By 2040-2069, mean surface air temperature is projected to rise 1.4-2.7°C compared to 1976-2005 levels.

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Still, the heat being recorded over recent weeks has taken scientists by surprise. “We had expected severe heat wave spells this year because El Nino is transitioning to neutral conditions and during such periods El Nino leaves a very strong mark causing severe heat spells. But what we are seeing is more serious than what we were anticipating. This can adversely impact anybody who is at home without cooling, even if they are not exerting themselves, because there is no relief at night either,” said M Rajeevan, former secretary, ministry of earth sciences and climate scientist.

The atmospheric conveyor belts

To understand why such occurrences could become more common as the climate heats up requires a look at how the Earth’s atmosphere works. In some ways, the atmosphere is made up of some conveyer belt-like systems that create air currents from high altitudes to low ones and from the west to east (in the northern hemisphere) or east to west in the southern half of the planet.

These circulation patterns are the result of changing seasons and in part the Earth’s rotation itself. These include what is known as the Hadley Cell or the Walker Circulation — the first has to do with how warm air from the equatorial region, where the sun shines the harshest, drifts towards the poles, descends and returns; the Walker Circulation is a similar pattern of west to east over the Pacific region.

Then there is the Jet stream in the upper latitudes, closer to the poles. Together, all these circulation patterns influence not just how wind blows laterally, but also vertically – and it is the vertical movement of air that creates areas of low or high pressure.

When air descends, it creates an area of high pressure, or an anti-cyclonic area, which in turn leads to warmer conditions (since compression, as a matter of physics, raises temperature). In some areas, such as in Mexico and parts of the United States at present, this descent of air has been known to create a heat dome effect, an area of heatwaves.

In India, experts said, a similar mechanism is at play. “An anticyclone is persisting over northwest India at a height of 3 to 5 km since May 16. When this happens, warm air is compressed and pushed towards the surface—just like closing something with a screwdriver. The downward flow of warm air leads to very high temperatures over the region. It is often disrupted by a western disturbance or a cyclonic circulation. But this time the anti-cyclone has been persisting continuously. Only today it was disrupted by an active Western Disturbance which will help reduce temperatures for around two days,” said M Mohapatra, director general, India Meteorological Department.

Between decades and years, there are often variations in these patterns, for instance, the occurrence of El Nino conditions when the equatorial pacific becomes warmer than usual. These are known as atmospheric teleconnections, and they form connections across thousands of miles, bringing hotter and drier temperatures in one region and colder or wetter in another.

The climate crisis

One of the outcomes of the climate crisis is that these patterns are now behaving in manners not seen before, leading to more extreme weather events. In general, experts HT spoke to said they foresee heatwaves such as the one heating India up at present to only become worse and far more common.

“Heat waves will not go away. They will be even more severe with higher temperature anomalies and for longer periods as per projections. This should worry us and the government should put in place measures immediately for common people adapt to this crisis,” added Rajeevan.

A second expert concurred. “This is global warming. Average temperature is increasing which is leading to intensification of heat waves. It is expected. Moreover, this has been an El Nino year so severe heatwaves were expected. Heatwave area is spatially increasing as per our analysis so new areas are recording extreme temperatures also. Warm nights will also increase,” said OP Sreejith, head, climate monitoring and prediction group, at IMD, Pune.

A third expert indicated more analysis is needed to establish it for sure, but occasionally, there indeed is a similar mechanism at play between what causes the heat dome such as the one seen over Mexico and parts of North America, and the heatwaves in north India – though they are not directly connected.

“Generally we don’t provide projections for next “few years” alone, due to multiple reasons including interannual and decadal variability. In general, heatwaves are projected to increase. Particularly, the number and intensity of day and night-time maximum temperatures are going to increase,” said Roxy Mathew Koll, climate scientist at Indian Institute of Tropical Meteorology.

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