Three phases
El Niño (warm), La Niña (cool), and Neutral, every two to seven years.
El Niño’s effect
Usually weakens the monsoon, but not always.
La Niña’s effect
Far more reliably boosts monsoon rainfall.
2026 status
A moderate-to-strong El Niño developed by June 2026.
The Basics
The Pacific’s Three Moods
- What ENSO is: short for the El Niño-Southern Oscillation. It’s a recurring shift in sea-surface temperatures and winds, across the tropical Pacific Ocean.
- Three phases: ENSO swings irregularly between El Niño (warm), La Niña (cool), and Neutral. This cycle repeats roughly every two to seven years, with no fixed schedule.
- Global reach: ENSO involves the whole tropical Pacific basin. So its effects ripple far beyond South America, reaching Australia, Southeast Asia, and South Asia alike.
- El Niño: happens when the central and eastern tropical Pacific, off the coast of Peru, warms up more than usual.
- La Niña: happens when that same region cools down more than usual, the exact opposite of El Niño.
True or False: ENSO swings between three phases, El Niño, La Niña, and Neutral, on a roughly two-to-seven-year cycle.
How the Swing Works
The Engine Behind the Swing
- Walker Circulation, normally: warm air rises over Indonesia. It travels east, high in the atmosphere, then sinks back down over the cooler eastern Pacific. This loop is the Walker Circulation.
- What powers it: pressure is high over the eastern Pacific, low over Indonesia. That difference drives the easterly trade winds along the ocean’s surface.
- What El Niño does: it weakens or reverses this circulation. Warm water and rising air shift eastward, and the pressure gradient that normally helps drive the monsoon weakens too.
- What La Niña does: the opposite. It strengthens the normal Walker Circulation, deepening the pressure gradient and reinforcing the winds that carry moisture into India.
Normal Pattern
Warm air rises over Indonesia, sinks over the eastern Pacific. Trade winds blow steadily west.
→
El Niño
Warm water and rising air shift east. The pressure gradient, and the monsoon’s push, both weaken.
→
La Niña
The normal loop strengthens instead. A deeper pressure gradient reinforces monsoon winds.
Not a Sure Thing
A Signal, Not a Guarantee
- Weaker winds: El Niño warming weakens the easterly trade winds that normally carry moisture toward India, which generally suppresses monsoon rainfall.
- Stronger winds: La Niña cooling strengthens those same easterly winds, which generally boosts monsoon rainfall above normal.
- Not automatic: since 1950, India has recorded 16 El Niño years. Only 7 of those actually went on to see below-normal monsoon rainfall.
- A second factor: this mixed record is why forecasters also track the Indian Ocean Dipole (IOD). El Niño alone isn’t read as a guaranteed bad-monsoon signal.
Think it through. If El Niño only produced a below-normal monsoon in 7 of 16 years, why do forecasters still treat it as an important warning sign?
Show the explanation
Less than half isn’t nothing. El Niño clearly tilts the odds toward a weaker monsoon, even if it doesn’t guarantee one every time. Other factors, like the Indian Ocean Dipole, can offset or reinforce that tilt in any given year. So forecasters treat El Niño as one important input among several, not a single switch that decides the outcome by itself.
A Steadier Pattern
La Niña’s Far More Reliable Record
- A stronger link: unlike El Niño’s mixed record, La Niña years show a much more consistent pattern. Indian monsoon rainfall came in above or around average in nearly all 16 studied La Niña years since records began.
- A recent run: starting in 2019, India logged four straight years of normal or above-normal monsoons. Three of those four years fell during La Niña conditions.
- 2024’s surplus: the 2024 monsoon season brought about 8% more rainfall than normal, 937.2 mm against a normal of 868.6 mm.
- Why it’s more reliable: La Niña’s cooling reinforces the Walker Circulation and the pressure gradient the monsoon depends on. El Niño works directly against that same gradient instead.
- The ONI: NOAA’s Oceanic Niño Index tracks a rolling three-month average temperature anomaly in the east-central Pacific. It’s the standard yardstick for ENSO’s strength worldwide.
- The strength categories: based on that anomaly, an event is classed weak, moderate, strong, or very strong. Very strong events cross roughly 2.0°C above normal.
- The big three: only three El Niño events since 1950 have reached “very strong” status: 1982-83, 1997-98, and 2015-16. The last measured around +2.6°C, the strongest on record.
True or False: El Niño has a far more reliable, consistent link to Indian monsoon rainfall than La Niña does.
The Real Exam Trap on This Topic
- The trap: options often mix up IOD’s Indian Ocean pattern with El Niño’s Pacific Ocean pattern. Some wrongly claim El Niño strengthens trade winds, when it actually weakens them.
- The fix: keep the oceans and the direction straight. IOD is Indian Ocean, east-west. ENSO is Pacific Ocean, east-west. Both El Niño and a positive IOD phase tend to suppress the monsoon.
- UPSC CSP 2017 Asked two things about IOD. Does it measure a Western Indian Ocean-Eastern Pacific gap? No, it’s within the Indian Ocean. Can it influence El Niño’s monsoon impact? Yes. View UPSC CSP 2017 Paper, Q66 →
- CDS-I 2022 Asked which of four listed effects is NOT actually caused by El Niño. El Niño weakens the equatorial trade winds; it does not push them toward the Indian Ocean. View CDS-I 2022 Paper, Q74 →
When It Went Wrong
When the Signal Turned Into a Crisis
- A pattern since independence: several of India’s worst droughts coincided with El Niño years, including 1972, 2002, and 2009.
- 2002: an especially severe drought. A 19% rainfall deficit hit 29% of the country, costing about 24 million tonnes of food grain.
- 2009: the third-worst drought since 1901, with a 23% rainfall deficit affecting roughly 59% of the country’s area.
- Why IMD watches it: the India Meteorological Department tracks ENSO’s status closely when forecasting each year’s monsoon. It remains one of the strongest single predictors of the monsoon’s overall strength.
Beyond the Fields
Beyond the Fields: An Economic Signal
- Rain-fed farming: around half of India’s net sown area is rain-fed. A delayed or deficient monsoon directly hits kharif crops like rice, cotton, soybean, and pulses.
- Government response: when the risk is high, the Agriculture Ministry runs weekly monitoring reviews. It also sets up state-specific contingency plans, including backup seed supplies for delayed sowing.
- Feeding inflation: research on India’s drought years found a strong link between monsoon deficits and food inflation. That inflation often shows up the following year, not just the same season.
- A real GDP drag: some estimates put the combined GDP hit from an El Niño-linked drought at 20 to 65 basis points. That drag spreads well beyond agriculture, into rural incomes and consumption.
- A ripple effect: when farm output drops, rural purchasing power weakens too. That, in turn, softens demand for goods and services well beyond the farm sector itself.
2025-2026 Update
A Strong El Niño Shadows the 2026 Monsoon
- The shift: ENSO moved from La Niña (August 2025-February 2026) to neutral, then crossed the El Niño threshold by June 2026.
- A fast intensification: WMO, NOAA, and IMD all pointed to a moderate-to-strong El Niño developing quickly. NOAA suggested it could persist into winter 2026-27.
- The forecast: IMD’s May 2026 long-range forecast projected seasonal rainfall at about 90% of the Long Period Average. It put the chance of a deficient monsoon at 60%.
- A partial counterweight: a projected positive IOD offers some offsetting support, echoing the wider point that El Niño rarely acts alone. Forecasters still doubt it can fully cancel out a strong El Niño’s effect.
Quick Q&A
Q: What is ENSO, in one line?
A: A recurring shift in Pacific Ocean temperatures and winds, swinging between El Niño (warm), La Niña (cool), and Neutral.
Q: Why does El Niño tend to weaken the Indian monsoon?
A: It shifts warm water and rising air eastward, weakening the pressure gradient that normally drives monsoon winds toward India.
Q: Is El Niño a guaranteed bad-monsoon signal?
A: No. Only 7 of 16 El Niño years since 1950 actually saw below-normal monsoon rainfall.
Q: What’s the IOD, and how does it relate to El Niño?
A: The Indian Ocean Dipole, a separate Indian Ocean temperature pattern that can strengthen or offset El Niño’s effect on the monsoon.
✅ Test Yourself
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