RAS question
El Nino is the anomalous warming of the eastern equatorial Pacific Ocean. How does a strong El Nino typically affect the Indian South-West Monsoon?
Correct answer: (A) It weakens the monsoon, leading to below-normal rainfall.
A strong El Nino typically weakens the Indian South-West Monsoon and is associated with below-normal rainfall.
Explanation
El Nino is the anomalous warming of the eastern equatorial Pacific and has a major teleconnection with the Indian monsoon. A strong event reduces the sea-surface temperature gradient between the Pacific and the Indian Ocean, weakening the Walker Circulation and cutting the moisture flow towards India. It therefore normally produces a weaker South-West Monsoon and below-normal rainfall, not a stronger one. The PIB release from the Ministry of Earth Sciences also states that, in general, the Indian summer monsoon is weaker than normal during an El Nino event, with the intensity of the event deciding the scale of impact. The 2002 and 2009 droughts fit this pattern.
Why the other options are wrong
- (B) El Nino cannot be treated as having no effect because the PIB release states that the Indian summer monsoon is generally weaker than normal during an El Nino event.
- (C) Strong El Nino reduces moisture flow and leads to below-normal monsoon rainfall, while the PIB release associates normal to above-normal rainfall with La Nina, not El Nino.
- (D) El Nino is associated with a weaker monsoon and below-normal rainfall; neither the mechanism nor the Press Information Bureau, Ministry of Earth Sciences supports a rule that El Nino delays onset while increasing total rainfall.
Concept
The ENSO-Indian monsoon teleconnection belongs to climatology and Indian physical geography. ENSO links a global ocean-atmosphere anomaly to Indian monsoon variability and drought-type outcomes, making it a recurring RAS theme.