El Niño-Southern Oscillation (ENSO) and Indian Monsoon
El Niño is the warm phase of the El Niño-Southern Oscillation (ENSO) cycle, characterised by anomalous warming of sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean. The coupled ocean-atmosphere system oscillates between the warm (El Niño) and cold (La Niña) phases on an irregular 2–7 year cycle.
- During El Niño, the Walker Circulation weakens: warm water shifts eastward in the Pacific, reducing convective activity over the Indian Ocean and suppressing monsoon rainfall over India and the subcontinent.
- El Niño years historically correlate with below-normal Indian monsoon rainfall; approximately 60% of El Niño events are associated with deficient monsoon (below 90% of long-period average).
- India's long-period average (LPA) for monsoon rainfall is approximately 87 cm over June–September.
- La Niña (cold phase) typically enhances Indian monsoon rainfall.
- Monitored by NOAA (USA) and the Bureau of Meteorology (Australia); declared when the Oceanic Niño Index (ONI) exceeds +0.5°C for at least five consecutive overlapping three-month periods.
- NOAA declared El Niño on June 11, 2026, with projections of the event persisting into the Northern Hemisphere winter of 2026–27 and potentially becoming a very strong event.
● Tracked since June 30, 2026 · last seen August 20, 2026 · updates as the daily brief publishes
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