'Triple-dip' La Nina improves air in North India, increases pollution in South region: Study

A new study has revealed that a rare and unusual ‘triple-dip’ La Niña event, influenced by climate change, had a significant impact on the air quality in different regions of India in the winter season of 2022-23.

Triple-dip' La Nina improves air in North India

La Niña is a natural phenomenon that occurs when the surface waters of the eastern and central Pacific Ocean become cooler than normal, affecting the atmospheric circulation and weather patterns around the world.

According to the study, published in the journal Elsevier, India experienced a unique ‘triple-dip’ La Niña event for three consecutive years from 2020 to 2023, which had a huge impact on the oceans and climate across the globe.

The study, conducted by a team of scientists led by Professor Gufran Baig of the National Institute of Advanced Studies (NIAS), found that this event triggered a strange trend in the air quality in India, where the northern parts of the country saw an improvement, while the peninsular regions witnessed a deterioration.

The study used a new NIAS-SAFAR air quality prediction model, which combines chemical-transport models with indigenously developed modern artificial intelligence algorithms, to analyse the data from various cities across India.

Air worsened in southern India

The results showed that the air quality worsened in cities across peninsular India, such as Mumbai, Coimbatore, Bengaluru, and Chennai, in the winter season of 2022-23, with an increase in the levels of fine particulate matter (PM 2.5), which can cause respiratory and cardiovascular diseases.

Mumbai recorded the highest increase in PM 2.5 levels, with a 30 per cent rise, followed by Coimbatore (28 per cent), Bengaluru (20 per cent), and Chennai (12 per cent).

The study attributed this to the cooler conditions, the strong high northerly winds, and the relatively slow winds near the surface, which trapped the pollutants and increased the cross-border pollution over peninsular India.

In contrast, the air quality improved in the northern parts of India, such as Ghaziabad, Rohtak, Noida, and Delhi, in the same period, with a decrease in the PM 2.5 levels, contrary to the trends seen in the recent decades.

Ghaziabad recorded the biggest improvement, with a 33 per cent reduction in pollution, followed by Rohtak (30 per cent) and Noida (28 per cent). Delhi, being the most severely affected and surrounded city, saw an improvement of about 10 per cent.

The study attributed this to the weak Western Disturbance, a unique wind pattern that brought rain, clouds, and rapid circulation, leading to a drastic improvement in the air quality in the north.

The study also noted that many northern Indian cities reached the five-year target set under the National Clean Air Program (NCAP) in no time, but the causes of this remain a mystery.

La Niña worsened air quality

The study’s co-author, RH Kripalani, a climate scientist at the Indian Institute of Tropical Meteorology (IITM), said that the winter of 2022-23 coincided with the final phase of the ‘triple-dip’ La Niña event, the first in the 21st century, which played a decisive role in the air quality in India.

He said that this phenomenon, influenced by climate change, affected the wind patterns on a large scale, and had implications for the global climate as well. RH Kripalani added that the findings of the study are warranted, as the air quality in the winter of 2023-24, when La Niña ends, is expected to return to normal levels.

He also said that the current findings show that we need to be conscious that extreme and unusual events in air pollution are directly or indirectly indicating climate change.

“Unless we focus on a long-term strategy to reduce the threat of anthropogenic emissions directly at the source, these kinds of revelations are going to grow exponentially,” he said.

The study suggested that apart from local emissions, rapidly changing climate is a major factor affecting the air quality, and called for more research and monitoring to understand the complex interactions between the climate and the air quality in India.

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