Could weather patterns predict India’s worst air pollution months?

New research has found that large-scale weather patterns explain much of the year-to-year variation in northern India’s winter air pollution and may make seasonal forecasts of severe air pollution possible.

Northern India experiences some of the world’s worst winter air pollution, with emergency control measures often introduced as mitigation. In major cities like Delhi, the Air Quality Index has reached levels above 999. more that 30 times the World Health Organization’s safety limit.

A new study finds that much of the year-to-year variation in winter pollution can be traced to large-scale weather systems and that these relationships could provide a warning of an unusually polluted winter, months in advance.

The study finds that 70% of the year-to-year variation in winter air pollution across northern India can be explained by the frequency of storm systems – known as western disturbances – that travel eastward from the Mediterranean region toward South Asia by strengthening vertical ventilation and bringing rain that helps clear pollution from the air. Winters with more frequent western disturbances therefore tend to experience lower air pollution levels, while winters with fewer of these storms are more susceptible to persistent severe pollution.

The researchers further found that the frequency of western disturbances is linked to ocean temperature patterns that are already evident during the preceding autumn. By taking advantage of that connection, they show that the overall severity of northern India’s winter pollution can be predicted approximately a season in advance.

Lead author Yuanyu Xie, an associate research scholar at the C-PREE said: ‘Currently, many of the most disruptive air-pollution measures are taken only after severe pollution is already developing. If scientists can anticipate the overall severity of the coming winter months ahead of time, governments, businesses, and communities will have more time to prepare.’

Winter air pollution is extremely problematic across northern India and during severe episodes, authorities can implement emergency measures to reduce emissions that include halting construction activities, placing restrictions on industry and limiting vehicle traffic.

Such interventions can reduce exposure, but they are difficult to implement on short notice. Seasonal forecasts could offer a more practical approach: rather than predicting the pollution concentration of a particular day months in advance, it could indicate whether the coming winter is likely to have relatively severe or mild pollution levels overall.

That additional information could provide lead time that would allow authorities to strengthen emissions enforcement before the pollution season begins, coordinate responses across jurisdictions and give businesses more time to prepare for potential restrictions.

Co-author Denise Mauzerall, a professor of Public and International Affairs and Civil and Environmental Engineering at Princeton University, said: ‘Emission controls will remain of paramount importance. However, we show that forecasts of winter pollution based on observations from the previous autumn can allow additional pollution controls to be arranged in advance of extreme pollution periods. This could provide time to plan and implement cost-effective controls that mitigate peak pollution concentrations in winter in northern India.’

The full research can be read here.

Photo: Pixabay