Climate Change

Warm Arctic waves, La Niña to blame for early heat waves, depressions: Experts

If the interaction between La Niña and the warm Arctic is happening, it is an impact of global warming

By Akshit Sangomla, Pulaha Roy
Published: Tuesday 29 March 2022
The India Meteorological Department (IMD) declared the season’s first heat wave and severe heat wave March 11 and the first depression March 3. Photo: iStock

Heat waves on land and depressions in the sea this year have started early in and around India, most probably because of an unexpected climatic anomaly which could, in turn, be linked to global warming.

The India Meteorological Department (IMD) declared the season’s first heat wave and severe heat wave March 11 and the first depression March 3.

Another depression also formed March 20, marking the first time in 130 years that two depressions formed in the month of March. Both depressions intensified into deep depressions and the second one threatened to even intensify into a rare March cyclone.

Another series of weird weather events were the three dust storms that affected Mumbai city and its surrounding region in January and February. The dust storms originated from the border of Pakistan and Afghanistan and affected Mumbai via the Arabian Sea.

The reason behind early heat waves, early depressions and the weird dust storms is the continued persistence of a north-south low pressure pattern that forms over India during winters when a La Niña phenomenon is occurring in the equatorial Pacific Ocean.

The sea surface temperatures over the east and central Pacific Ocean become cooler-than-average during La Niña. This affects the trade winds flowing over the ocean surface through change in wind stress.

The trade winds carry this weather disturbance elsewhere and affect large parts of the world. In India, the phenomenon is mostly associated with wet and cold winters. Therefore, the current effect of La Niña is completely unexpected.

“The La Niña produced a north-south pressure pattern over India as expected during the winter but it seems to be persisting in some form. The weird dust storm, the early deep depressions, one of which threatened to form a cyclone and the heatwaves are all part of this weird persistence,” Raghu Murtugudde, a climate scientist at the University of Maryland, United States, said. The weird persistence of the La Niña is also affecting other regions of the world.

“The temperatures over western Russia, down to Kazakhstan and over Pakistan, Afghanistan, all the way into Spain and Portugal were more than 10 degree Celsius warmer during February.

“The last time we had a La Niña persisting for three years was during 1998-2000 and 2000 also had a cyclone in March. So the La Niña is interacting with the high latitude pattern I think, basically the warm Arctic region sending atmospheric waves down,” Murtugudde said.

If the interaction between the La Nina and the warm Arctic is in fact happening then it is an impact of global warming induced by human greenhouse gas emissions.

While both deep depressions in the Bay of Bengal did not impact the Indian mainland, the second one caused some rainfall over the Andaman and Nicobar Islands, before moving towards Myanmar and making landfall there.

The dust storms drastically brought down Mumbai’s air quality for days after the events happened in January and February.

There have been 13 more heat wave days (total 14) and nine more severe heat wave days (total 10), mostly in the western and northern parts of the country, since the first heat wave on March 11.

This is according to data from India Meteorological Department analysed by Down To Earth.

Eight states and one Union territory of Jammu and Kashmir have undergone heat waves in this period and five of these states and Jammu and Kashmir have undergone severe heat waves.

Gujarat was the most affected as some part of the state has scorched under a severe heat wave or heat wave for 11 days of March. Within Gujarat, the worst affected were the Saurashtra and Kutch regions which suffered from heat waves for 10 days.

The second-worst affected state was Madhya Pradesh, especially the western part of the state which suffered from heat waves for nine days.

An interesting aspect of the heat waves this season has been their occurrence in the mountain states of Himachal Pradesh, Uttarakhand and union territory of Jammu and Kashmir.

This would hasten the melting of snow and glaciers in these regions which, in turn, would affect the availability of water for the people. Apart from causing massive impacts to human health, even deaths, heat waves can impact agricultural crop yields as they can often lead to drought.

Down To Earth

DTE mapped air temperature over 40 degrees Celsius across the subcontinent and compared it with the climatic condition persisting last year (2021) to corroborate the intensity and scale of heatwaves for March 2022.

The difference is stark. The heat waves ranged from Afghanistan in the west to Myanmar in the east. Heat waves in the same regions of India are still underway and are going to persist till at least April 2, according to the latest forecasts by IMD.

The La Niña phenomenon may also persist for the next few months and may affect the monsoon rains as well. The World Meteorological Organization (WMO) has estimated that there is a 65 per cent chance of La Nina continuing from March to May.

On the other hand, the National Oceanic and Atmospheric Administration (NOAA) has given a 53 per cent chance for La Nina to continue till August. This persistence could bring in more weird weather and even affect the monsoon season this year in India.

“If La Niña reemerges, then we should have a normal-to-above normal monsoon,” Murtugudde said.

He also highlighted the fact that the formation of cyclones in the last few years have disrupted the formation and the progress of monsoon winds over India, which could get repeated this year as well.

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