El Niño

• Definition: El Niño is a periodic climate phenomenon involving unusual warming of sea-surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean.
• ENSO: El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO).
• Trade Winds: During El Niño, the normally prevailing easterly trade winds weaken, allowing warm surface water to move eastward.
• Upwelling: Weakened trade winds reduce the upwelling of cold, nutrient-rich water along the western coast of South America.
• Atmospheric Circulation: El Niño modifies the Walker Circulation, thereby disturbing global atmospheric circulation and rainfall patterns.
• Global Impact: It can cause droughts in some regions, excessive rainfall/flooding in others, and widespread temperature anomalies.

India — Important Prelims Points

• Indian Monsoon: El Niño is generally associated with weaker Southwest Monsoon rainfall over India, although this relationship is not absolute.
• Agriculture: Weak monsoon can affect crop production, irrigation and food security.
• Temperature: El Niño can contribute to above-normal temperatures and heat stress in several regions.
• Indian Ocean Dipole (IOD): A positive IOD can partly offset the adverse influence of El Niño on the Indian monsoon.

Prelims MCQ

Q. With reference to El Niño, consider the following statements:

1. It involves abnormal warming of the central and eastern equatorial Pacific Ocean.
2. It is the warm phase of ENSO.
3. It is generally associated with weakening of the trade winds.
4. It always results in deficient monsoon rainfall over India.

Which of the statements given above are correct?

(a) 1, 2 and 3 only
(b) 1 and 2 only
(c) 2, 3 and 4 only
(d) 1, 2, 3 and 4

Answer: (a) 1, 2 and 3 only

Explanation: El Niño involves warming of the central/eastern equatorial Pacific and weakening of trade winds. It increases the probability of a weak Indian monsoon but does not always cause deficient rainfall.