El Niño and La Niña

  • IASbaba
  • March 3, 2023
  • 0
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Context: India is experiencing a colder winter than normal with the La Niña is going on for a record-breaking third consecutive year also known as the ‘Triple dip’ La Nina.

  • Forecasts for the 2023 fall and winter are predicting that El Niño will occur with more than a 50% probability.

About the El Niño, La Niña and ENSO:

  • El Niño is the warming of seawater in the central-east Equatorial Pacific that occurs every few years.
  • During El Niño, surface temperatures in the equatorial Pacific rise, and trade winds — east-west winds that blow near the Equator — weaken.
  • Normally, easterly trade winds blow from the Americas towards Asia.
  • Due to El Niño, they falter and change direction to turn into westerlies, bringing warm water from the western Pacific towards the Americas.
  • It occurs every 3-6 years and lasts for about 9-12 months.
  • It can cause droughts, flooding, and changes in temperature.
  • It can lead to below-normal rainfall, which affects India’s agricultural sector.

Outcomes of El Nino:

  • Disruptions in the food chain:
    • The phenomena of upwelling, where nutrient-rich waters rise towards the surface, is reduced under El Niño.
      • This in turn reduces phytoplankton.
    • Thus, fish that eat phytoplankton are affected, followed by other organisms higher up the food chain.
  • Disruptions in the overall ecosystem:
    • Warm waters also carry tropical species towards colder areas, disrupting multiple ecosystems.
  • Alterations in wind and weather patterns:
    • Since the Pacific covers almost one-third of the earth, changes in its temperature and subsequent alteration of wind patterns disrupt global weather patterns.
    • El Niño causes dry, warm winters in Northern U.S. and Canada and increases the risk of flooding in the U.S. gulf coast and southeaster U.S.
      • It also brings drought to Indonesia and Australia.

About La Niña:

  • La Niña sees cooler than average sea surface temperature (SST) in the equatorial Pacific region.
  • Trade winds are stronger than usual, pushing warmer water towards Asia.
  • It is a phenomenon that is the colder counterpart of El Niño.
  • It occurs when ocean temperatures in the equatorial Pacific drop to lower-than-normal levels.

Outcomes of La Nina:

  • On the American west coast, upwelling increases, bringing nutrient-rich water to the surface.
  • Pacific cold waters close to the Americas push jet streams — narrow bands of strong winds in the upper atmosphere — northwards.
    • This leads to drier conditions in Southern U.S., and heavy rainfall in Canada.
  • La Niña has also been associated with heavy floods in Australia.
  • Two successive La Niña events in the last two years caused intense flooding in Australia, resulting in significant damage.

ENSO Cycle:

  • El Nino–Southern Oscillation (ENSO) is an irregularly periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean.
  • Every three to seven years, the surface waters across tropical Pacific Ocean warm or cool by 1°C to 3°C, compared to normal.
  • The warming phase of the sea temperature is known as El Nino and the cooling phase as La Nina.
  • Thus, El Nino and La Nina are opposite phases of what is known as the El Nino-Southern Oscillation (ENSO) cycle.
  • These deviations from normal surface temperatures can have large-scale impacts not only on ocean processes, but also on global weather and climate.

Impact on Cyclone Formation and Monsoons in 2023

El Niño and Monsoon Deficit:

  • A transition from La Niña winter to El Niño summer tends to produce a large monsoon deficit of around 15%.
  • This means weaker pre-monsoon and monsoon circulations, and weaker vertical shear, which can favour enhanced cyclone formation.
  • However, intrapersonal or sub seasonal variability in sea-surface temperature and winds also plays an important role in cyclogenesis over the northern Indian Ocean.
  • Overall, the net effect is for cyclogenesis to be subdued in an El Niño year.

Monsoon Deficit in 2023:

  • If an El Niño state emerges by summer, India will likely have a deficit monsoon in 2023.
  • Some research indicates that the Indian Ocean dipole may compensate for the negative effects of an El Niño, but it is not clear whether there is a robust relation between the dipole and the summer monsoon, nor whether the dipole will evolve in the “right” way this year.

Vagaries of Monsoon:

  • The pre-monsoon cyclones are susceptible to warming in the Arctic region and could affect the onset of the summer monsoon.
  • The Bay of Bengal has been receiving freshwater from heavy rains and high river runoffs, which tend to sneak into the Arabian Sea, produce surface warming, and build up subsurface heat.
  • These changes together may create favourable conditions for the formation of bigger and badder cyclones, especially if the circulation and the vertical shear are weak.

Government steps to mitigate the impact of El Niño:

  • Pradhan Mantri Fasal Bima Yojana (PMFBY): It is a crop insurance scheme launched by the government to protect farmers from crop loss due to various natural calamities, including drought, floods, and other weather-related events.
  • Mission Amrit Sarovar: It is a scheme of developing 75 ponds in each district by the government to help reduce the dependence on rainfall.
  • Soil Health Card scheme: This scheme aims to promote soil testing and provide farmers with the necessary information to help farmers to better manage their crops during periods of drought or other weather-related events.
  • National Food Security Mission (NFSM): It aims to increase the productivity of crops in rainfed areas through the adoption of better farming practices and the use of new technologies.
  • National Watershed Development Project for Rainfed Areas (NWDPRA): This project aims to promote sustainable watershed management practices in rainfed areas to improve soil moisture and water availability for crops during drought periods.
  • National Agricultural Insurance Scheme (NAIS): This scheme provides financial assistance to farmers in case of crop loss due to natural calamities, including drought and other weather-related events.
  • Rashtriya Krishi Vikas Yojana (RKVY): This scheme aims to promote agriculture development through various initiatives, including the development of rainfed agriculture and the use of modern technologies to improve crop productivity during drought periods.
  • Pradhan Mantri Krishi Sinchai Yojana (PMKSY): It aims to promote efficient use of water resources in agriculture and increase water use efficiency to deal with drought and other weather-related events.

Source:  The Hindu

Previous Year Questions

Q.1) Consider the following statements:

  1. High clouds primarily reflect solar radiation and cool the surface of the Earth.
  2. Low clouds have a high absorption of infrared radiation emanating from the Earth’s surface and thus cause warming effect.

Which of the statements given above is/are correct? (2022)

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2

Q.2) Consider the following statements:

  1. In the tropical zone, the western sections of the oceans are warmer than the eastern sections owing to the influence of trade winds.
  2. In the temperate Zone, westerlies make the eastern sections of oceans warmer than the western sections

Which of the statements given above is/are correct? (2021)

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 and 2


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