El Niño, La Niña, and ENSO

Mains Marks Booster     5th August 2023        
Samadhaan

Niño

  • El Niño refers to the warming of seawater in the central-east Equatorial Pacific that happens every few years. During El Niño, surface temperatures in the equatorial Pacific rise, and trade winds weaken.
  • Normally, easterly trade winds blow from the Americas towards Asia, but during El Niño, they change direction and become westerlies, bringing warm water from the western Pacific towards the Americas.
  • El Niño occurs every 3-6 years and lasts for about 9-12 months. It can cause droughts, flooding, and changes in temperature.
  • El Niño can lead to below-normal rainfall, impacting India's agricultural sector.

Outcomes of El Niño

  • Disruptions in the food chain: The reduction of upwelling and phytoplankton due to El Niño affects fish and organisms higher up the food chain.
  • Disruptions in the overall ecosystem: Warm waters carry tropical species towards colder areas, disrupting multiple ecosystems.
  • Alterations in wind and weather patterns: Changes in Pacific temperature and wind patterns affect global weather, causing dry, warm winters in Northern U.S. and Canada, increased flooding risk in the U.S. Gulf Coast and Southeastern U.S., and drought in Indonesia and Australia.

La Niña

  • La Niña is characterized by cooler than average sea surface temperatures in the equatorial Pacific region.
  • Trade winds during La Niña are stronger than usual, pushing warmer water towards Asia.
  • It is the colder counterpart of El Niño and occurs when ocean temperatures in the equatorial Pacific drop to lower-than-normal levels.

Outcomes of La Niña

  1. Upwelling increases on the American west coast, bringing nutrient-rich water to the surface.
  2. Pacific cold waters near the Americas push jet streams northwards, leading to drier conditions in Southern U.S. and heavy rainfall in Canada.
  3. La Niña has been associated with heavy floods in Australia, as seen in the past two years.

El Nino and Southern Oscillation (ENSO)

  • El Niño–Southern Oscillation (ENSO) refers to irregular variations in winds and sea surface temperatures over the tropical eastern Pacific Ocean.
  • Surface waters across the tropical Pacific Ocean warm or cool by 1°C to 3°C compared to normal every three to seven years.
  • The warming phase is El Niño, and the cooling phase is La Niña. El Niño and La Niña are opposite phases of the ENSO cycle, impacting ocean processes, weather, and climate globally.

Impact on Cyclone Formation and Monsoons in 2023

El Niño and Monsoon Deficit

  • A transition from La Niña winter to El Niño summer typically leads to a large monsoon deficit of around 15%.
  • Weaker pre-monsoon and monsoon circulations and weaker vertical shear favor enhanced cyclone formation.
  • However, sub seasonal variability in sea-surface temperature and winds also plays a role in cyclogenesis over the northern Indian Ocean. Overall, cyclogenesis tends to be subdued during an El Niño year.

Monsoon Deficit in 2023

  • If an El Niño state emerges by summer, India is likely to experience a deficit monsoon in 2023.
  • The Indian Ocean dipole may compensate for the negative effects of El Niño, but the relation between the dipole and the summer monsoon is not fully understood.

Vagaries of Monsoon

  • Pre-monsoon cyclones are affected by warming in the Arctic region, potentially impacting the onset of the summer monsoon.
  • Heavy rains and high river runoffs in the Bay of Bengal contribute to surface warming in the Arabian Sea, creating favorable conditions for cyclone formation if circulation and vertical shear are weak.

  • The India Meteorological Department (IMD) forecasts 'normal' rainfall in July, 2023 with a 6% variation from the average of 28 cm. 
  • Central and south peninsular India may experience normal to above-normal rainfall, while northwest, northeast, and southeast peninsular India may see below-normal rainfall. 
  • This forecast is significant as it contradicts expectations for below-normal rainfall during an El Niño year.


Government Steps to Mitigate the Impact of El Niño

  1. Pradhan Mantri Fasal Bima Yojana (PMFBY): Crop insurance scheme to protect farmers from crop loss due to natural calamities, including drought, floods, and weather-related events.
  2. Mission Amrit Sarovar: Scheme to develop 75 ponds in each district to reduce dependence on rainfall.
  3. Soil Health Card scheme: Promotes soil testing to help farmers better manage crops during droughts or weather-related events.
  4. National Food Security Mission (NFSM): Aims to increase crop productivity in rainfed areas through better farming practices and technology adoption.
  5. National Watershed Development Project for Rainfed Areas (NWDPRA): Promotes sustainable watershed management to improve soil moisture and water availability during drought periods.
  6. National Agricultural Insurance Scheme (NAIS): Provides financial assistance to farmers in case of crop loss due to natural calamities, including drought and weather-related events.
  7. Rashtriya Krishi Vikas Yojana (RKVY): Aims to promote agriculture development, including rainfed agriculture and modern technologies for improved crop productivity during drought periods.
  8. Pradhan Mantri Krishi Sinchai Yojana (PMKSY): Promotes efficient use of water resources in agriculture to deal with drought and weather-related events, increasing water use efficiency.
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