El Niño–Southern Oscillation (ENSO) and the Indian Monsoon

ENSO (El Niño–Southern Oscillation) refers to periodic fluctuations in sea surface temperatures (SSTs) and atmospheric pressure in the tropical Pacific Ocean. The warm phase (El Niño) weakens the Walker Circulation and reduces moisture influx into the Indian subcontinent, historically causing below-normal or deficient monsoon years in India. The cool phase (La Niña) has the opposite effect, often enhancing monsoon rainfall. About 40% of inter-annual variability in India's summer monsoon rainfall is under ENSO influence, and Indian summer monsoon rainfall shows roughly 10% inter-annual variability around the LPA.