El Niño Explained: Causes, Mechanism and Effects on India and the World

India’s 2026 southwest monsoon ended at just 87% of its long period average, the fourth weakest since 2001. The cause lay thousands of kilometres away, in the tropical Pacific, where sea surface temperatures have climbed to levels the World Meteorological Organization (WMO) describes as off its charts. That phenomenon is El Niño, and understanding its effects is essential for any aspirant studying climate, agriculture or the economy.

What Is El Niño?

“El Niño” is Spanish for “the little boy” or the Christ child. Peruvian fishermen gave the name to a warm current that appeared off their coast around Christmas and ruined fish catches.

Scientifically, El Niño is the warm phase of the El Niño Southern Oscillation (ENSO), a natural climate cycle in the tropical Pacific with three phases:

Phase	Pacific condition	Recurrence
El Niño (warm)	Central and eastern Pacific warmer than normal	Every 2 to 7 years
Neutral	Near-normal conditions	Most common
La Niña (cool)	Central and eastern Pacific cooler than normal	Every 2 to 7 years

The “Southern Oscillation” is the atmospheric half: a see-saw in air pressure between the eastern Pacific (Tahiti) and the western Pacific (Darwin, Australia). Ocean and atmosphere change together, which is why they are studied as one system.

Normal Conditions in the Pacific

Trade winds blow from east to west along the equator.
They push warm surface water towards Indonesia and Australia, so the western Pacific is warm and low-pressure.
Off Peru, cold, nutrient-rich water rises from below, a process called upwelling. This supports some of the world’s richest fisheries.
Air rises over the warm west Pacific (bringing rain) and sinks over the cool east Pacific (keeping it dry). This loop is the Walker circulation.

What Changes During El Niño

Feature	Normal year	El Niño year
Trade winds	Strong, east to west	Weaken or reverse
Warm water pool	Western Pacific	Shifts to central/eastern Pacific
Upwelling off Peru	Strong	Suppressed
Thermocline (eastern Pacific)	Shallow	Deepens
Rising air and rainfall	Indonesia, Australia	Central/eastern Pacific, Peru
Southern Oscillation Index	Positive or near zero	Negative

The key point: when the rising branch of the Walker circulation moves east, air sinks over the western Pacific and the Indian Ocean region. Sinking air suppresses cloud formation, and this is how a Pacific event weakens rainfall in India.

How El Niño Is Measured

Scientists track sea surface temperature in the Niño 3.4 region of the equatorial Pacific. An El Niño is declared when the three-month average anomaly reaches +0.5°C or more.

From February 2026, the US agency NOAA switched to the Relative Oceanic Niño Index (RONI). It subtracts the average warming of the whole tropical belt from the Niño 3.4 reading, so that global warming does not inflate El Niño values. This makes events from different decades comparable.

Effects of El Niño on India

1. Monsoon: El Niño years carry a higher risk of below-normal southwest monsoon rainfall. The link is strong but not absolute. In 1997, a very strong El Niño coincided with a normal monsoon because a positive Indian Ocean Dipole offset it (covered in Part 3 of this series).

2. Agriculture: About half of India’s net sown area is rain-fed. Weak rains hit kharif crops such as rice, pulses and oilseeds, lower reservoir levels and reduce soil moisture for the rabi season.

3. Economy and prices: Lower output pushes up food inflation and can reduce rural demand. Electricity demand rises for irrigation pumps and cooling.

4. Temperature: El Niño adds heat to the atmosphere. Warmer winters and harsher heatwaves the following summer are common. Since El Niño usually peaks around December, its effects spill into the next year.

Global Effects of El Niño

Region	Typical impact
Peru, Ecuador	Heavy rain, floods; collapse of anchovy fisheries
Indonesia, Australia	Drought, forest fires
Southern Africa	Drought, crop failure
East Africa	Heavier short-season rains, floods
Southern USA	Wetter winters
Atlantic Ocean	Fewer hurricanes
Coral reefs	Mass bleaching from warm water
Global average	Record or near-record temperatures

El Niño and Climate Change

Scientists agree that El Niño is a natural cycle, but how warming will change it remains debated. Some studies project more frequent extreme El Niño events, while others find the evidence uncertain. What is clearer is that El Niño now sits on top of a warmer baseline, so its heat impacts are amplified.

Way Forward for India

Forecasting: strengthen IMD’s dynamical models and district-level advisories.
Agricultural contingency plans: short-duration and drought-tolerant varieties, timely seed supply.
Water management: watershed development, micro-irrigation, regulated groundwater use.
Price management: buffer stocks, open market sales and calibrated trade measures.
Heat preparedness: state and city Heat Action Plans ahead of summer.

Conclusion

El Niño shows how tightly the world’s oceans and atmosphere are connected. A change in Pacific trade winds can reduce rice output in Odisha and raise vegetable prices in Delhi. For India, the answer lies not in predicting El Niño alone but in building agriculture and water systems resilient enough to absorb its shocks.

Read next in this series: La Niña and the ENSO Cycle | Indian Ocean Dipole and MJO: Why El Niño Does Not Always Mean Drought

UPSC Relevance

GS Paper I: “Important Geophysical phenomena”; “Salient features of world’s physical geography”; ocean currents and climatology.
GS Paper III: “Major crops, cropping patterns”; “Disaster and disaster management”; food inflation under “Indian Economy”.
Prelims: mechanism, Niño 3.4, RONI, Walker circulation, Southern Oscillation.
Essay and Interview: climate risk, food security, India’s climate adaptation.

Mains Practice Question

Q. “El Niño is a Pacific phenomenon with Indian consequences.” Explain the mechanism of El Niño and discuss its effects on India’s agriculture and economy. (15 marks, 250 words)

Prelims Practice Question

Q. Consider the following statements about El Niño:

During El Niño, the trade winds over the equatorial Pacific become stronger.
Upwelling of cold water off the coast of Peru weakens during El Niño.
The Relative Oceanic Niño Index (RONI) adjusts the Niño 3.4 temperature anomaly for warming across the wider tropics.

Which of the statements given above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Answer: (b)
Explanation: Trade winds weaken or reverse during El Niño, so statement 1 is wrong. Weaker winds suppress upwelling off Peru. RONI subtracts the average tropical sea surface temperature anomaly from the Niño 3.4 reading.

Mains 2014 (GS I): Most of the unusual climatic happenings are explained as an outcome of the El-Nino effect. Do you agree?
Prelims 2017: With reference to the “Indian Ocean Dipole (IOD)” sometimes mentioned in the news while forecasting Indian monsoon, which of the statements is/are correct? (Answer: an IOD phenomenon can influence an El Niño’s impact on the monsoon.)

FAQs

What is El Niño in simple words?
El Niño is an unusual warming of the central and eastern Pacific Ocean that occurs every two to seven years and changes weather patterns worldwide.

How does El Niño affect the Indian monsoon?
It shifts the rising air of the Walker circulation eastward, causing air to sink over the Indian Ocean region. This suppresses clouds and usually weakens monsoon rainfall.

Does every El Niño cause drought in India?
No. A positive Indian Ocean Dipole can offset its impact, as happened in 1997.

What is the difference between El Niño and La Niña?
El Niño is the warm phase of ENSO and usually weakens India’s monsoon. La Niña is the cool phase and usually strengthens it.

What is RONI in El Niño?
The Relative Oceanic Niño Index is NOAA’s main El Niño measure since February 2026. It removes the effect of overall tropical warming from Pacific temperature readings.