El Niño Emerges in Pacific: How ENSO, IOD and IMD's 2026 Forecast Shape India's Monsoon

The trigger event: The IMD, in its monthly ENSO and Indian Ocean Dipole bulletin, declared that El Niño conditions have developed over the equatorial Pacific Ocean and are likely to intensify during the June–September southwest monsoon. This makes 2026 an "El Niño year," a category Indian forecasters watch closely because of its historical link with weaker monsoons.

The phenomenon: El Niño refers to the abnormal and sustained warming of surface waters in the central and eastern equatorial Pacific Ocean, off the north-western coast of South America. The name, Spanish for "the little boy" or "the Christ Child," was given by Peruvian fishermen who noticed the unusually warm waters appearing around Christmas. Its cooler counterpart, La Niña, means "the little girl." El Niño is not a single event in the Indian Ocean; it originates thousands of kilometres away in the Pacific but transmits its influence to India through the global atmosphere.

ENSO defined: El Niño is one phase of a larger coupled ocean–atmosphere system called the El Niño–Southern Oscillation (ENSO). "El Niño" describes the oceanic warming, while the "Southern Oscillation" describes the see-saw of atmospheric pressure between the eastern and western Pacific. Because the ocean and atmosphere act together, ENSO is studied as a single linked system with three phases: the warm phase (El Niño), the cool phase (La Niña), and the in-between Neutral phase.

The normal (neutral) state: In a normal year, strong easterly trade winds blow across the Pacific from South America towards Indonesia. These winds drag warm surface water westward, piling it up over the western Pacific "warm pool" near Indonesia, while cold, nutrient-rich water rises (upwelling) along the South American coast. This sets up the Walker Circulation — a giant east–west loop of air in which warm, moist air rises over the western Pacific (creating low pressure, clouds and rain) and sinks over the cooler eastern Pacific (creating high pressure and dry conditions).

What changes during El Niño: During El Niño the trade winds weaken or even reverse. Warm water that was held in the west sloshes back eastward, upwelling off South America is suppressed, and the centre of rising air and rainfall shifts eastward into the central Pacific. The Walker Circulation weakens and shifts, dragging the zone of convection away from the Indian Ocean region.

The Bjerknes feedback: The system is self-reinforcing. Weaker winds allow the eastern Pacific to warm; the warming further reduces the east–west temperature difference, which weakens the winds still more. This positive feedback loop, named after meteorologist Jacob Bjerknes, is why a small initial warming can grow into a full El Niño event.

The Niño 3.4 region and index: Scientists divide the equatorial Pacific into monitoring boxes (Niño 1+2, Niño 3, Niño 3.4 and Niño 4). The Niño 3.4 region (roughly 5°N–5°S, 120°W–170°W) is the most widely used for declaring ENSO phases because it best captures the warming that affects global weather. The Niño 3.4 index is the sea surface temperature anomaly — the departure from the long-term average — within this box.

The declaration threshold: An El Niño is generally declared when the sea surface temperature anomaly in the Niño 3.4 region crosses about +0.5°C (and is expected to persist), while a value of about –0.5°C or colder signals La Niña. NOAA uses the Oceanic Niño Index (ONI), the three-month running average of the Niño 3.4 anomaly, and looks for the threshold to be sustained across several overlapping seasons.

Grading the strength: By ONI value, an event is broadly classed as weak (+0.5 to +0.9°C), moderate (+1.0 to +1.4°C), strong (+1.5 to +1.9°C) and very strong (+2.0°C or above). NOAA's projection that the 2026 event could reach "very strong" at its peak means the Niño 3.4 anomaly may exceed +2°C around the winter of 2026–27.

The atmospheric measure: The "Southern Oscillation" half of ENSO is tracked using the Southern Oscillation Index (SOI), based on the surface air-pressure difference between Tahiti (central Pacific) and Darwin (Australia). A strongly negative SOI accompanies El Niño, confirming that the atmosphere — not just the ocean — has switched into the warm phase.

The teleconnection: A "teleconnection" is a link between climate conditions in two far-apart regions. The Indian monsoon depends on strong rising air and convection over the warm waters around the Indian Ocean and the maritime continent (Indonesia–Malaysia region). When El Niño shifts the rising branch of the Walker Circulation eastward into the central Pacific, the descending (sinking) branch tends to sit over the Indian Ocean and South Asia. Sinking air suppresses cloud formation and rainfall, weakening the monsoon circulation and reducing the moisture carried onto the subcontinent.

The historical pattern: Statistically, many of India's severe drought years have coincided with El Niño years. This is why a confirmed El Niño typically lowers monsoon forecasts. However, the relationship is probabilistic, not guaranteed — El Niño raises the chance of a deficient monsoon but does not "decide" it.

The IOD defined: The Indian Ocean Dipole is the Indian Ocean's own ocean–atmosphere see-saw, often called the "Indian Niño." It is measured by the sea surface temperature difference between two poles: a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the ocean south of Indonesia (eastern Indian Ocean). It was first identified by Indian researchers in 1999.

The three phases: In a positive IOD, the western Indian Ocean is warmer than the east; this enhances moisture supply and generally strengthens the Indian monsoon. In a negative IOD, the east is warmer than the west, which tends to suppress the monsoon. A neutral IOD has little dipole signal.

The interaction with ENSO: The IOD can amplify or offset El Niño's impact on India. A strong positive IOD has, in the past, partly cancelled the drying effect of an El Niño (for example, in 1997). In 2026, the IMD has assessed the IOD as neutral and likely to stay so for much of the year, meaning it is not expected to provide a strong protective counterbalance to the developing El Niño — a key reason the monsoon outlook is cautious.

The nuance: No. While El Niño increases the likelihood of below-normal rainfall, not every El Niño year has produced a drought, and the strength of the event does not map neatly onto monsoon outcomes. The eventual rainfall depends on the interplay of several drivers — the IOD, the Madden–Julian Oscillation (an eastward-moving pulse of cloud and rainfall), regional pressure systems, and the spatial and temporal distribution of rain within the season.

Why distribution matters: A modest seasonal shortfall can be managed if rain is well spread across regions and timed correctly; conversely, even a "normal" total can hurt agriculture if long dry spells strike during critical sowing or flowering stages. For Indian agriculture, the timing of rainfall in July and August over the rain-fed core zone often matters more than the headline national percentage.

Agriculture and food security: The southwest monsoon delivers the bulk of India's annual rainfall, and a majority of the net sown area is still rain-fed and dependent on it for the kharif (monsoon) crop. A deficient monsoon, especially over the central and western core zone, can stress the output of pulses, oilseeds, rice, cotton and sugarcane, with downstream effects on food prices and rural incomes.

Heat and water: Subdued rainfall is typically accompanied by above-normal temperatures and a higher chance of heatwaves, along with stress on soil moisture, groundwater and reservoir levels that affect drinking water and irrigation.

Global footprint: ENSO is a planetary-scale phenomenon. El Niño years are associated with droughts in Indonesia, Australia and parts of Africa, heavy rain and flooding along the coasts of Peru and Ecuador, and a tendency towards record-warm global temperatures, since the ocean releases stored heat into the atmosphere.

Strengthen contingency planning: ready stocks of short-duration and drought-tolerant seed varieties, fodder reserves and crop-specific advisories so farmers can adjust sowing decisions early.

Prioritise water security: efficient reservoir management, recharge of groundwater, micro-irrigation (drip and sprinkler) and revival of traditional water-harvesting structures to buffer dry spells.

Promote crop diversification: encourage less water-intensive crops and millets in vulnerable zones, supported by minimum support price and procurement signals.

Sharpen monitoring and early warning: continue close tracking of the Niño 3.4 index, IOD and sub-seasonal drivers, and issue timely district-level advisories through IMD and the agriculture extension network.

Protect rural livelihoods: keep employment-guarantee works, crop insurance (PMFBY) and price-stabilisation mechanisms ready to cushion any rainfall shock.

Build long-term resilience: invest in climate-resilient agriculture, watershed development and accurate seasonal forecasting to reduce dependence on a single season's rainfall.