Air

Long-term wind patterns over Delhi have changed, say scientists

A possible reason could be major changes in the withdrawal of monsoon from the region and the anti-cyclonic circulations that are formed in this period

 
By Akshit Sangomla
Last Updated: Thursday 15 November 2018
Wind patterns
The sun sets over Gurugram.   Credit: Getty Images The sun sets over Gurugram. Credit: Getty Images

Long-term wind patterns over Delhi have changed in the past few years, scientists have revealed. This is having major implications on the pollution levels in the city.

“The frequency of winds coming in from the north-west direction has increased in the past few years. Exact quantification of this increase will require more studies which we are now carrying out but a definite pattern is clearly visible”, Gufran Beig of the System of Air Quality and Weather Forecasting and Research (SAFAR) at the Indian Institute of Tropical Meteorology (IITM), Pune told Down to Earth.

“There could be many reasons for this change of wind patterns but one possible reason could be major changes in the withdrawal of monsoon from the region and the anti cyclonic circulations that are formed in this period”, Beig added.

Beig’s statement came even as a mild shower of rain on the night of November 13 brought relief to the choking city. On November 14, air pollution levels in Delhi-NCR were classified as “unhealthy”, down from “hazardous” and “severe” in the past weeks. This could be because rain would have brought the pollutants, especially the particulate matter (both PM10 and PM2.5), down to the surface and cleared the air. If this would not have happened, Delhi was staring at a blanket ban on private vehicles. In this case, weather helped the cause of fighting air pollution in Delhi but it can also have disastrous effects.

Weather conditions play a crucial role in determining the pollution levels of a city or region. They also form an important component of severe smog events that have been witnessed repeatedly over Delhi in the past few years, especially during winter months. For example, in the first week of November 2017, there was severe smog over Delhi and one of the factors responsible for this was a north-westerly wind that had brought in pollutants from Punjab, Haryana and Pakistan. Similarly, around the festival of Diwali in 2016, an anti-cyclonic circulation had reduced the wind speeds in Delhi, making the pollutants settle down near the surface and stick to the water vapour, aggravating the conditions severely. In 2018 too, the air quality had plummeted to hazardous levels even though the Supreme Court had ordered a partial ban on the bursting of crackers in Delhi. The role of wind speeds and directions on air pollution levels in the current year still needs to be studied.

But it is not only the winter months that have seen such changes in wind patterns. It was also observed earlier this year. The entire northern part of India had been plunged into a dust bowl-like condition in April and May, decreasing the air quality drastically. It was observed that the wind patterns over Delhi and its surrounding regions had changed from the usual westerly winds to winds coming from the eastward direction. The easterly winds had brought in moisture from the Bay of Bengal and this had lead to severe dust and thunder storms in the region. In the middle of June this year, an anti-cyclonic circulation from Rajasthan had brought in dust from the desert, significantly increasing (839 microgram/cubic metre) the PM10 pollution in Delhi.

Tracking and studying the weather can play a crucial role in not only explaining the occurrence of air pollution but also in predicting severe air pollution and smog events in the future. 

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