Rare ‘triple-dip’ La Nina event behind unusually good air quality in India in 2022-23, says study

Rare ‘triple-dip’ La Nina event behind unusually good air quality in India in 2022-23, says study

A rare triple-dip La-Nina event, prolonged by climate change, set off a unique trend in the winter of 2022–2023, where air quality improved in north India while pollution levels increased in peninsular India.

The unusual “triple-dip” event of three years in a row of La Niña conditions (2020–23) has a global influence on the ocean and climate.

A team of scientists led by Gufran Beig, Chair Professor, National Institute of Advanced Studies, conducted a study that highlighted the importance of quickly changing climate in relation to air quality, in addition to local emissions.

The study, which was published in the Elsevier Journal, shows that, in contrast to previous decades, the air quality in Indian cities on the peninsula deteriorated during the winter of 2022–2023 while improving in the country’s north.

Among the north Indian cities, Ghaziabad recorded the most noteworthy improvement with a drop of 33 per cent, followed by Rohtak (30 per cent) and Noida (28 per cent). Delhi exhibited an improvement of around 10 per cent.

However, with a 30 per cent increase in PM2.5 levels, Mumbai saw the worst degradation, followed by other Indian peninsula cities like Coimbatore (28 per cent), Bengaluru (20 per cent), Chennai (12 per cent), etc.

Several North Indian cities almost surpassed the five-year-long target set under the National Clean Air Programme in no time. What caused this had been a puzzle, said the researchers.

“The winter of 2022-23 coincided with the last phase of an unusual triple-dip La Niña event, the first in the 21st century. This phenomenon, influenced by climate change, impacted the large-scale wind pattern, playing a decisive role in preventing stagnation conditions in north Indian cities and thus improving air quality,” said R H Kripalani, a climate scientist at the Indian Institute of Tropical Meteorology and co-author of the report.

On the contrary, he said that it brought calmer conditions to Indian towns on the peninsula, hastened transboundary pollution, and dramatically worsened the quality of the air.

“The dominance of higher northerly winds at the transport level forced an influx, along with relatively slower winds near the surface, trapping pollutants in peninsular India and increasing PM2.5 concentration. Conversely, feeble western disturbances, unique wind patterns, and the absence of rain, clouds, and faster ventilation led to a significant improvement in air quality in the north,” Kripalani said.

The scientists used the recently created cutting-edge NIAS-SAFAR air quality forecasting model, which blends a chemical transport model with a contemporary artificial intelligence algorithm created locally, to validate their theory.

“Our findings are vindicated as the air quality in the winter of 2023-24, when La Nina ended, returned to normal levels,” Beig said.

“The findings of the current paper suggest that we need to wake up to the fact that extreme and unusual occurrences in air pollution phenomena are directly or indirectly manifestations of climate change,” he said.

“Such revelations, in all probability, are set to increase by leaps and bounds unless we focus on a long-term strategy to reduce the menace of anthropogenic emissions directly at the source. That would be a win-win situation for both air quality and climate change,” he said.

(With inputs from agencies)