The Indian Ocean Dipole (IOD) is a climate pattern caused by the difference in sea surface temperature between the western Indian Ocean and the eastern Indian Ocean.
It affects rainfall, monsoon behaviour, droughts, floods and cyclones in countries around the Indian Ocean, including India, Australia, Indonesia and East Africa.
Basic Meaning
The Indian Ocean does not warm uniformly. Sometimes the western part of the Indian Ocean, near the Arabian Sea and the east coast of Africa, becomes warmer than the eastern part near Indonesia and Australia. At other times, the opposite happens.
This temperature contrast changes wind patterns, moisture movement and rainfall distribution.
The IOD is measured through the Dipole Mode Index (DMI), which compares sea surface temperature anomalies between:
- Western Indian Ocean
- Eastern Indian Ocean
When the temperature difference becomes significant, the IOD enters a positive or negative phase.
Positive IOD
A Positive IOD occurs when the western Indian Ocean becomes warmer than normal and the eastern Indian Ocean becomes cooler than normal.
This usually leads to more convection and rainfall over the western Indian Ocean region, while Indonesia and parts of Australia may become drier.
For India, a positive IOD often supports the southwest monsoon because warmer waters in the western Indian Ocean can increase moisture supply towards the Indian subcontinent.
Typical impacts include:
- stronger rainfall tendency over India
- reduced rainfall over Indonesia and Australia
- wetter conditions over East Africa
- possible support to monsoon during El Niño years
- increased convection over the Arabian Sea side
A positive IOD can sometimes reduce the negative impact of El Niño on the Indian monsoon, though it does not always fully cancel it.
Negative IOD
A Negative IOD occurs when the eastern Indian Ocean near Indonesia becomes warmer than normal and the western Indian Ocean becomes cooler than normal.
This shifts convection towards Indonesia and Australia.
For India, a negative IOD may weaken monsoon rainfall or reduce moisture support from the Indian Ocean.
Typical impacts include:
- more rainfall over Indonesia and Australia
- relatively drier conditions over East Africa
- weaker support for Indian monsoon rainfall
- reduced convection over western Indian Ocean
- possible stress on Indian rainfall if combined with El Niño
Neutral IOD
A Neutral IOD means there is no strong temperature contrast between the western and eastern Indian Ocean.
In this phase, the IOD does not significantly support or suppress monsoon rainfall.
Other climate drivers such as El Niño-Southern Oscillation, Madden-Julian Oscillation, monsoon trough position, Arabian Sea warming and local weather systems may become more important.
As of mid-June 2026, the Australian Bureau of Meteorology reported neutral IOD conditions, with the IOD index at −0.13°C on 14 June 2026. IMD’s June 2026 extended range forecast also noted neutral IOD conditions over the Indian Ocean.
IOD and Indian Monsoon
The IOD is important for India because it can influence the southwest monsoon.
The relationship is not mechanical, but the broad pattern is:
| IOD Phase | Likely Effect on India |
| Positive IOD | Can support monsoon rainfall |
| Negative IOD | Can weaken rainfall tendency |
| Neutral IOD | Limited direct influence |
The IOD becomes especially important when it interacts with El Niño.
El Niño usually weakens the Indian monsoon. But if a strong positive IOD develops at the same time, it can partially offset El Niño’s drying effect.
For example, some past El Niño years did not produce severe drought in India because a positive IOD helped support rainfall.
In 2026, IMD and Reuters reports indicated concern over El Niño conditions during the monsoon, while the IOD was expected to remain neutral or not provide strong support.
IOD and Global Weather
The IOD affects several regions around the Indian Ocean.
A positive IOD may cause:
- higher rainfall in East Africa
- drought-like conditions in Indonesia
- drier conditions in parts of Australia
- stronger monsoon support in parts of India
A negative IOD may cause:
- wetter conditions in Indonesia and Australia
- reduced rainfall in East Africa
- weaker Indian Ocean support for India’s monsoon
This makes the IOD a major climate driver in the Indo-Pacific region.
Difference Between IOD and El Niño
The Indian Ocean Dipole and El Niño are different climate phenomena.
IOD occurs in the Indian Ocean, while El Niño occurs in the Pacific Ocean.
| Basis | Indian Ocean Dipole | El Niño |
| Ocean | Indian Ocean | Pacific Ocean |
| Measurement | Temperature difference between western and eastern Indian Ocean | Warming of central/eastern equatorial Pacific |
| India impact | Can strengthen or weaken monsoon depending on phase | Usually weakens Indian monsoon |
| Positive phase | Warmer western Indian Ocean | Warmer eastern/central Pacific |
| Main relevance | Indian Ocean rainfall and monsoon modulation | Global climate and monsoon suppression |
The Indian monsoon is influenced by both. A strong El Niño with neutral or negative IOD is more worrying for Indian rainfall than an El Niño accompanied by a strong positive IOD.
Significance
The Indian Ocean Dipole is significant because it helps explain why monsoon rainfall varies from year to year.
Its importance lies in:
- influencing Indian monsoon rainfall
- modifying El Niño’s impact
- affecting drought and flood risks
- shaping rainfall over East Africa, Indonesia and Australia
- influencing agriculture and water availability
- helping seasonal rainfall prediction
- affecting cyclone and convection patterns in the Indian Ocean
For India, IOD is closely watched by IMD because agriculture, reservoirs, groundwater recharge, food inflation and rural incomes depend heavily on monsoon rainfall.
Limitations
IOD is only one factor behind monsoon behaviour.
A positive IOD does not guarantee good rainfall, and a negative IOD does not automatically mean drought. The monsoon is influenced by multiple systems working together.
Other important factors include:
- El Niño-Southern Oscillation
- snow cover over Eurasia and Himalayas
- land-sea thermal contrast
- monsoon trough position
- Madden-Julian Oscillation
- Arabian Sea warming
- Bay of Bengal low-pressure systems
- local rainfall distribution
This is why seasonal forecasts use several climate indicators instead of relying only on IOD.
Importance
The Indian Ocean Dipole is a major ocean-atmosphere climate pattern of the Indian Ocean.
A positive IOD can support the Indian monsoon, a negative IOD can weaken rainfall support, and a neutral IOD has limited direct influence.
Its real importance lies in how it interacts with El Niño and other monsoon drivers, making it a key factor in India’s seasonal climate forecasting.
