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El Nino Phenomenon

Context: Several international agencies predicted that there’s a 50 percent chances of El Nino in the second half of 2023.

About El-Nino

  • El Nino is a Spanish word that means ‘The Little Boy’.
  • The occasional climatic change and development of warm ocean surface waters along the coast of Peru and Ecuador are called El Nino effect.
  • Mechanism: In El Nino, the trade winds which blow along the Equator from east to west weakened and created high air pressure in the Western Pacific Ocean and low air pressure in the eastern Pacific Ocean.
    • Due to this, the surface water moves towards the coast of northern South America.
    • The central and east Pacific ocean warms up for six months, creating an El Nino effect.
    • During El Nino, warming the central and east pacific oceans reduces the usual upwelling of cold water, ultimately reducing the nutrient content in that region.
  • An El Niño this year could increase the planet’s average surface temperature by more than 1.5° C from pre-industrial levels.
El Nino Phenomenon
El Nino Phenomenon

Effects of El-Nino on India

  • Monsoon: El Nino and Indian monsoons are inversely related.
  • Droughts: The most prominent droughts in India – six of them – since 1871 have been El Nino droughts, including the recent ones in 2002 and 2009
    • However, not all El Nino years led to a drought in India. For instance, 1997/98 was a strong El Nino year but there was no drought (Because of IOD).
    • On the other hand, a moderate El Nino in 2002 resulted in one of the worst droughts.
  • Agrarian economy: El Nino directly impacts India’s agrarian economy as it tends to lower the production of summer crops such as rice, sugarcane, cotton, and oilseeds.

About La Nina

  • It is an atmospheric wind and sea surface temperature (SST) variability phenomenon occurring over the equatorial Pacific.
  • It refers to an abnormal cooling of the central and eastern Pacific Ocean waters off the coasts of Ecuador and Peru.
    • Such cooling (SSTs falling 0.5 degrees Celsius or more below a 30-year average for at least five successive three-month periods) is a result of strong trade winds blowing west along the equator, taking warm water from South America towards Asia.
    • The warming of the western equatorial Pacific, then, leads to increased evaporation and concentrated cloud-formation activity around that region, whose effects may percolate to India as well.
  • It is characterized by a negative Oceanic Niño Index (ONI value) exceeding or equal to minus 0.5 degrees i.e ENSO (El Niño-Southern Oscillation) cycle has entered a “neutral” phase.
  • La Nina is associated with good rainfall in India.
El Nino La Nina
The trade winds, which blow from east to west, diminish during an El Niño. The trade winds that blow from east to west intensify during La Nina.
Warm seas build up over the eastern Pacific Ocean during El Nino. Warm water builds up across the western Pacific Ocean during La Nina.
Over the western Pacific, the El Nino is packed with high air surface pressure. Low air surface pressure is present during La Nina across the eastern Pacific Ocean.
El Nino has low wind speeds. The wind speed is particularly high during La Nina.
Coriolis force strength declines during El Nino. However, during La Nina, the Coriolis force becomes stronger.
In the eastern Pacific Ocean and surrounding nations like Chile, Peru, and Ecuador, El Nino causes excessive rainfall. La Nina causes drought-like conditions over the eastern Pacific Ocean, affecting neighboring nations like Chile, Peru, and Ecuador.

El Niño Southern Oscillation (ENSO)

  • The combination of El Niño, La Niña, and the neutral state between the two opposite effects is called the El Niño Southern Oscillation (ENSO).
  • The phenomenon was discovered by Sir Gilbert Walker.

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