Indian Ocean Dipole: What is it, and can it rescue India’s faltering 2026 monsoon

The 2026 southwest monsoon season has recorded below-normal rainfall, with the India Meteorological Department (IMD) forecasting seasonal rainfall at approxi...

What Happened

The 2026 southwest monsoon season has recorded below-normal rainfall, with the India Meteorological Department (IMD) forecasting seasonal rainfall at approximately 92% of the Long Period Average (LPA), driven primarily by a developing strong El Niño in the equatorial Pacific.
A positive Indian Ocean Dipole (IOD) is forecast to develop towards the latter part of the monsoon season (post-August), which could partially offset the drying effect of El Niño.
Climate scientists have flagged the interplay between IOD and El Niño as critical to understanding India's evolving monsoon variability — reviving interest in ocean-atmosphere coupling as a forecasting tool.

Static Topic Bridges

Indian Ocean Dipole (IOD)

The Indian Ocean Dipole (IOD) is a coupled ocean-atmosphere phenomenon characterised by a sustained sea surface temperature (SST) anomaly between the western and eastern tropical Indian Ocean. First identified in 1999, it oscillates between positive, negative, and neutral phases on irregular multi-year cycles, exerting significant influence on rainfall patterns across the Indo-Pacific region.

Positive IOD: Warmer-than-normal SSTs in the western Indian Ocean (off the Arabian Sea and East Africa coast) and cooler-than-normal SSTs in the eastern Indian Ocean (off Sumatra and Indonesia). Associated with stronger westward winds and enhanced moisture transport toward the Indian subcontinent — generally leads to above-normal monsoon rainfall in India.
Negative IOD: Cooler SSTs in the west, warmer SSTs in the east. Weakens moisture transport toward India, suppressing monsoon rainfall.
Neutral IOD: SST gradient remains within normal bounds; monsoon outcome depends on other factors (ENSO, Madden-Julian Oscillation, etc.).
Historically, positive IOD partially offset El Niño's drying impact on India in years such as 1983, 1994, and 1997.

Connection to this news: The 2026 forecast projects a positive IOD developing late in the monsoon season, potentially providing partial relief from below-normal rainfall induced by the concurrent El Niño.

El Niño-Southern Oscillation (ENSO) and Its Relationship with IOD

El Niño-Southern Oscillation (ENSO) is a periodic warming (El Niño) or cooling (La Niña) of sea surface temperatures in the central and eastern tropical Pacific Ocean, coupled with atmospheric pressure changes (the Southern Oscillation). El Niño events typically lead to weaker southwest monsoon rainfall over India due to reduced moisture availability and altered atmospheric circulation.

ENSO and IOD interact through the Walker Circulation — El Niño-driven anomalies in Pacific SSTs shift the Walker Circulation, which can in turn trigger SST dipole patterns over the Indian Ocean.
Positive IOD and La Niña conditions both independently favour above-normal monsoon; their co-occurrence amplifies the effect. Conversely, negative IOD and El Niño together can severely suppress monsoon rainfall.
Many IOD events occur independently of ENSO, driven by regional ocean-atmosphere dynamics within the Indian Ocean itself — the relationship is bidirectional, not one-way.
A strong 2026 El Niño is forecast for the Pacific; IMD projects below-normal monsoon (92% of LPA) as the primary consequence.

Connection to this news: The 2026 monsoon deficit is primarily El Niño-driven; the developing positive IOD introduces uncertainty — it may moderate (but not eliminate) the rainfall shortfall.

Walker Circulation

The Walker Circulation is a large-scale east-west atmospheric circulation pattern driven by SST gradients across ocean basins. In the Indian Ocean context, it describes the zonal circulation between regions of anomalous convection (rising air over warm SSTs) and subsidence (sinking air over cool SSTs).

During a positive IOD event, the warm western Indian Ocean drives convective uplift, pulling moisture-laden winds westward and southward toward India — enhancing southwest monsoon rainfall.
During El Niño, the Pacific Walker Circulation weakens: warm SSTs in the central-eastern Pacific draw convection eastward, reducing Indian Ocean moisture flux and weakening the monsoon.
ENSO affects the Indian Ocean through an "atmospheric bridge" — Pacific SST anomalies alter the Walker Circulation, which then modulates Indian Ocean SSTs and can trigger or suppress IOD events.

Connection to this news: Understanding the Walker Circulation is essential for interpreting why simultaneous El Niño (Pacific) and positive IOD (Indian Ocean) signals produce competing effects on India's monsoon.

India's Southwest Monsoon Mechanism

India's southwest monsoon (June–September) delivers approximately 70–75% of the country's annual rainfall and is critical for agriculture, water reservoirs, and the broader economy. It is driven by the differential heating of the Indian landmass and the Indian Ocean, which creates a pressure gradient drawing moisture-laden winds from sea to land.

The monsoon's onset over Kerala typically occurs around June 1 (±7 days). The system advances northward, covering the entire country by mid-July.
IMD defines "normal" monsoon as rainfall within ±10% of the LPA (currently 87 cm for June–September). Below 90% is classified as "below normal"; below 80% as "drought."
Two critical ocean-atmosphere drivers of interannual monsoon variability are ENSO (Pacific) and IOD (Indian Ocean). Other factors include the Madden-Julian Oscillation (MJO), Arctic sea-ice extent, and Eurasian snow cover.
Kharif crop sowing (rice, pulses, oilseeds, cotton) is directly dependent on southwest monsoon distribution and timing.

Connection to this news: The 2026 monsoon shortfall forecast has direct implications for kharif crop production, food inflation, and rural demand — a recurring UPSC theme linking physical geography to economy and governance.

Key Facts & Data

IOD was first identified and described in the scientific literature in 1999.
IMD's 2026 southwest monsoon forecast: approximately 92% of LPA (±5% error), classified as below normal.
A positive IOD in 1997 helped India receive near-normal rainfall despite a concurrent strong El Niño — a widely cited example of IOD-ENSO interference.
The Indian Ocean's western warm pool (west of ~70°E) is the key SST driver during a positive IOD event.
IOD events typically peak during August–October, coinciding with the later phases of India's monsoon season — explaining why late-developing positive IOD has limited impact on early monsoon months.
India receives ~880 mm of rainfall during the June–September southwest monsoon season (LPA for 1971–2020 baseline).