About:

Findings:

• The combination of El Niño, La Niña, and the neutral state between the two opposite effects is called the El Niño Southern Oscillation (ENSO).
• Southern oscillations are large-scale changes in sea level pressure in the tropical Pacific region.

El Niño phenomenon:

• El Niño is the warming of sea water 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.
• 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.
• Warm waters also carry tropical species towards colder areas, disrupting multiple ecosystems.
• Since the Pacific covers almost one-third of the earth, changes in its temperature and subsequent alteration of wind patterns disrupt global weather patterns.
• Impacts:
  • El Niño causes dry, warm winter in Northern U.S. and Canada and increases the risk of flooding in the U.S. gulf coast and south-eastern U.S. It also brings drought to Indonesia and Australia.

La Niña:

• La Niña is the opposite of El Niño.
• 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.
• 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.
• Impacts:
  • 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.

Impact on India’s monsoons:

• In India, El Niño causes weak rainfall and more heat, while La Niña intensifies rainfall across South Asia, particularly in India’s northwest and Bangladesh during the monsoon.
• At present, India, like the rest of the globe, is witnessing an extended ‘triple dip’ La Niña.