Indian Ocean Dipole

The Indian Ocean Dipole (IOD) quantifies the difference in sea surface temperature (SST) between the western and eastern areas of the Indian Ocean (Figure 1).

Indian Ocean Dipole regions

Fig. 1. Indian Ocean Dipole regions.
Source: NOAA/ESRL/PSD

The IOD has positive, negative, and neutral phases. During the positive phase, the western Indian Ocean is warmer than the eastern Indian Ocean, whereas the reverse is true during the negative phase of the IOD (Figure 2). The IOD varies irregularly in time but is usually strongest during August–November.

Sea surface temperature patterns of positive and negative IOD

Fig. 2. SST Patterns of positive and negative IOD.
Source: NOAA/ESRL/PSD

While the IOD is not always strong during ENSO events, it is unlikely for the IOD to be negative during El Niño and positive during La Niña. A positive IOD event in combination with an El Niño event enhances the El Niño impacts. Likewise, a negative IOD event in combination with a La Niña event enhances the impacts of the latter. 

The IOD strongly influences precipitation over East Africa during the October–December season: a positive IOD results in enhanced precipitation over East Africa while a negative IOD results in reduced precipitation, as illustrated by the December precipitation anomalies in Figure 3.

Precipitation impacts of the IOD in December

Fig. 3. Precipitation impacts of the IOD in December.
Source: NOAA/ESRL/PSD

The impacts of a positive or negative IOD on FEWS NET regions are shown in the table below.

IOD Impacts
Region Season Positive IOD Negative IOD
Eastern Horn Oct-Dec Wet Dry
Southern Africa Nov-Mar Minimal impact Minimal impact
West Africa Apr-Jul Minimal impact Minimal impact
Central America
and the Caribbean
Jun-Aug Minimal impact Minimal impact
Central Asia Oct-May Wet Dry
Central Asia Jul-Aug Minimal impact Minimal impact
Note: The East Africa March–May season is not included in this table, as a negative or positive IOD is a very unlikely occurrence in this region at that time.

Source: NOAA/ESRL/PSD

About FEWS NET

The Famine Early Warning Systems Network is a leading provider of early warning and analysis on food insecurity. Created by USAID in 1985 to help decision-makers plan for humanitarian crises, FEWS NET provides evidence-based analysis on approximately 30 countries. Implementing team members include NASA, NOAA, USDA, USGS, and CHC-UCSB, along with Chemonics International Inc. and Kimetrica.
Learn more About Us.

Link to United States Agency for International Development (USAID)Link to the United States Geological Survey's (USGS) FEWS NET Data PortalLink to U.S. Department of Agriculture (USDA)
Link to National Aeronautics and Space Administration's (NASA) Earth ObservatoryLink to the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service, Climage Prediction CenterLink to the Climate Hazards Center - UC Santa BarbaraLink to KimetricaLink to Chemonics