A climate pattern where Pacific Ocean surface temperatures warm above normal, often weakening the Indian monsoon and bringing drought to parts of Asia.
phenomenaWhat is El Niño?
El Niño is a recurring climate pattern in which the surface waters of the central and eastern tropical Pacific Ocean become significantly warmer than average. The warming usually lasts 9–12 months and recurs every 2–7 years. Together with its opposite phase, La Niña (cooler Pacific), it forms the El Niño–Southern Oscillation (ENSO) — the single largest source of year-to-year climate variability on Earth.
The name comes from Peruvian fishermen who noticed the warm waters appearing around Christmas — El Niño de Navidad, “the Christ Child.”
ENSO matters enormously for South Asia because it can weaken or delay the Indian monsoon, raise summer temperatures, and affect winter rainfall. The 2015-16 and 2023-24 El Niño events both reduced Indian monsoon rainfall and intensified pre-monsoon heatwaves.
How El Niño works
In neutral conditions, trade winds blow from east to west across the equatorial Pacific, pushing warm surface water toward Indonesia and Australia. This pile-up of warm water in the western Pacific feeds the moist, rising air that powers the Asian and Australian monsoons. Meanwhile, cool deep water rises along the South American coast — a process called upwelling.
During El Niño, trade winds weaken or even reverse:
- Warm surface water sloshes back east toward South America.
- The Pacific warm pool — and its rainfall — shifts eastward.
- Indonesia and the western Pacific become drier.
- South America’s west coast becomes warmer and wetter.
- The whole atmospheric circulation (Walker Circulation) is disrupted.
This redistribution of warmth and rainfall ripples through global weather patterns for the next year.
El Niño’s impact on South Asia
The relationship between El Niño and the Indian monsoon is statistically strong but not deterministic. El Niño years see reduced monsoon rainfall about 60% of the time, but other factors (Indian Ocean Dipole, Madden-Julian Oscillation, snow cover) can offset or amplify the effect.
Typical El Niño effects in South Asia:
- Weakened southwest monsoon (June–September) — often 5–15% below normal, sometimes more.
- Delayed monsoon onset in Kerala, sometimes by 1–2 weeks.
- More intense pre-monsoon heatwaves in April–May.
- Drought risk in central and southern India, parts of Pakistan and Sri Lanka.
- Lower water reservoir levels affecting summer hydropower and agriculture.
- Increased AQI because reduced rainfall fails to clean the air.
Notable historical El Niño years and Indian monsoon impact:
- 1997-98: Very strong El Niño but Indian monsoon was near-normal — counter-example.
- 2002: Strong El Niño; severe drought across India (monsoon 19% below normal).
- 2009: Strong El Niño; below-normal monsoon (23% deficit).
- 2015-16: Strong El Niño; consecutive monsoon deficits.
- 2023-24: Strong El Niño; weakest Indian monsoon in 5 years.
El Niño’s impact on Southeast Asia
While South Asia experiences variable effects, Southeast Asia and Indonesia are reliably drier during El Niño:
- Drought in Indonesia, Malaysia, Philippines, Thailand.
- Massive peat-fire seasons in Sumatra and Kalimantan, causing transboundary haze that smothers Singapore, Malaysia, southern Thailand.
- Reduced tropical-cyclone activity in the western Pacific.
- Coral bleaching from elevated sea-surface temperatures.
How El Niño is monitored
The most-watched index is the Oceanic Niño Index (ONI) — a 3-month running mean of sea-surface temperature anomalies in the Niño 3.4 region (5°N–5°S, 120°W–170°W). An ONI of:
- +0.5°C or warmer = El Niño conditions (warm phase)
- −0.5°C or cooler = La Niña conditions (cool phase)
- In between = ENSO-neutral
NOAA, the Australian Bureau of Meteorology, and the Japan Meteorological Agency all publish ENSO forecasts. IMD’s monsoon forecast explicitly accounts for ENSO state.
El Niño and climate change
A long-running question: does global warming make El Niño more frequent or intense? The IPCC AR6 concludes that extreme El Niño events are likely to become more frequent under continued warming, but baseline ENSO activity may not change dramatically. What is certain is that El Niño’s impacts — heat, drought, fires — are now layered on top of the underlying warming trend, making them more dangerous.
For South Asian planners, the implication is that El Niño years should be treated as drought + heatwave risk windows, requiring early water-storage and crop-planning interventions.
Frequently asked questions
Is El Niño happening now? Check the NOAA Climate Prediction Center or India Meteorological Department. ENSO state is updated monthly. The 2023-24 El Niño ended in mid-2024 and the Pacific has been moving toward neutral or weak La Niña conditions since.
Does El Niño always mean a bad monsoon for India? No — only about 60% of El Niño years see deficient Indian monsoon. The Indian Ocean Dipole (IOD) and the Madden-Julian Oscillation can offset El Niño’s effects. A “positive IOD” in particular can rescue an El Niño monsoon.
What is the difference between El Niño and La Niña? They are opposite phases of ENSO. El Niño = warm central/eastern Pacific. La Niña = cool central/eastern Pacific. La Niña often brings stronger monsoons to India and more cyclones to the Bay of Bengal.
How long does El Niño last? Typically 9–12 months, occasionally up to 18 months. Strong El Niños usually develop in spring (March–May), peak in winter (November–February), and fade by the following spring.
Where can I see how El Niño is affecting my city? Mausam Online shows live weather and AQI data on every city page. For the broader monsoon outlook, see our Monsoon India 2026 guide (Hindi) and live forecasts for Delhi, Mumbai, Chennai, Dhaka.