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Impact of La Niña on Air Quality in India

Why is it in the news?

  • An unprecedented triple-dip La Niña event, exacerbated by climate change, has adversely affected air quality in India.

Link between Pollution and Winter Months in India

  • During the months of October to January, northern Indian cities, particularly Delhi and its adjoining regions, experience very high concentrations of 5, a fine particulate matter that poses significant health risks.
  • Various meteorological factors such as temperature, moisture, heaviness in air (inversion layer), wind speed, and direction play crucial roles in trapping pollutants close to the surface of the Earth.
  • Pollution levels are exacerbated during this period due to the burning of agricultural waste in states like Punjab and Haryana, with pollutants being transported to Delhi and surrounding areas through prevailing wind patterns.
  • In contrast, the western and southern parts of India have historically maintained relatively lower levels of pollution owing to their proximity to the Arabian Sea and the Indian Ocean.

 Rare ‘Triple Dip’ La Niña Event

  • The winter of 2022-23 witnessed an unprecedented triple-dip La Niña event, marking the first occurrence of such an event in the 21st century.
  • La Niña events typically lead to cooler sea surface temperatures in the equatorial Pacific region, influencing global weather patterns.
  • Climate change has exacerbated the intensity and frequency of La Niña events, leading to unusual climatic phenomena and impacts.
  • The 2022-23 winter season saw a unique pattern where air quality worsened in peninsular Indian cities but improved in northern India, particularly Delhi.
  • This anomalous behaviour was attributed to the influence of the triple-dip La Niña event on large-scale wind patterns, which prevented stagnation conditions in north Indian cities, thereby facilitating better dispersion of pollutants and improving air quality.
Understanding El Niño, La Niña and ENSO

El Niño:

·       El Niño refers to the warming of seawater in the central-east Equatorial Pacific that occurs irregularly every few years.

·       Effect on Trade Winds: The warming of sea surface temperatures weakens the east-to-west trade winds near the Equator.

Global Weather Patterns:

·       Northern U.S. and Canada: El Niño often results in dry, warm winters in these regions.

·       U.S. Gulf Coast and Southeastern U.S.: It increases the risk of flooding due to enhanced rainfall.

·       Indonesia and Australia: El Niño is associated with drought conditions, leading to water shortages and agricultural losses.

·       Impact on India: In India, El Niño typically brings weak monsoon rainfall and increased heat, adversely affecting agriculture and water resources.

La Niña:

·       La Niña is the opposite of El Niño and is characterized by cooler than average sea surface temperatures in the equatorial Pacific.

·       Strengthening Trade Winds: During La Niña events, trade winds are stronger than usual, pushing warmer water towards Asia.

Global Weather Patterns:

·       Southern U.S.: La Niña leads to drier conditions in the Southern U.S., exacerbating droughts.

·       Canada: It often results in heavy rainfall and increased snowfall in Canada, leading to flooding.

·       Australia: La Niña is associated with heavy rainfall and flooding events in Australia, especially in regions prone to cyclones.

·       Impact on India: La Niña intensifies rainfall, particularly in northwest India, leading to above-average monsoon precipitation and sometimes causing floods.

El Niño Southern Oscillation (ENSO)

·       ENSO refers to the combined effects of El Niño, La Niña, and the neutral state between them.

·       ENSO involves large-scale changes in sea level pressure in the tropical Pacific region, influencing global atmospheric circulation patterns.

·       During the neutral phase, sea surface temperatures in the equatorial Pacific are near average, and there is no significant impact on global weather patterns.

·       ENSO plays a crucial role in modulating climate variability around the world, affecting temperature, precipitation, and weather extremes in various regions.

 

 

 Impact of Wind Direction

  • Anomalies in wind direction during the winter of 2022 played a crucial role in influencing air quality across different regions of India.
  • Traditionally, the prevailing wind direction during winter months blows from northwest to southeast, carrying pollutants from agricultural burning in Punjab and Haryana towards Delhi and the Gangetic plains.
  • However, in 2022, the wind circulation pattern deviated from the norm, with winds blowing in a north-south direction.
  • This atypical wind pattern caused pollutants to bypass Delhi and surrounding areas, instead traveling over Rajasthan and Gujarat towards southern regions.
  • Similarly, in Mumbai, changes in wind direction led to the accumulation of pollutants within the city due to persistent offshore winds that prevented dispersion.

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