The Indian Ocean Dipole (IOD), also referred to as the Indian Niño, is a seasonal climate index that is one of the most vital considerations in seasonal forecasting for the Indian Ocean’s rim countries. The IOD is caused by a variance in sea surface temperatures (SST) and rainfall between the western and eastern parts of the Indian Ocean, resulting in these areas becoming alternatively warmer and then colder. There are three phases of the IOD, neutral, positive, and negative, each of the phases occurring every 3-5 years. Positive or negative IOD phases usually begin in the spring or summer, peak during autumn, and ends in late November.
The neutral phase of the Indian Ocean Dipole is characterized by temperatures that are close to normal across the tropical Indian Ocean. During this phase, water from the Pacific Ocean flows between the Islands of Indonesia, with westerly winds blowing along the equator. The air rises above this area and falls over the western Indian Ocean. During the negative phase of this seasonal climate phenomenon, the westerly winds intensify, resulting in warmer waters concentrating in the eastern Indian Ocean, south of Indonesia, and cooler than normal waters concentrating off the east coast of Africa. As a result of this SST irregularity, heavier rainfall in the eastern Indian Ocean and dryer conditions in the western Indian Ocean ensues. The opposite phenomenon occurs during the positive phase of the IOD, with westerly winds weakening significantly and easterly winds forming. Warmer waters are concentrated off of the African east coast and cooler waters are concentrated south of Indonesia. Consequently, heavier rainfall occurs in countries bordering the western Indian Ocean and countries in the eastern part of the Indian Ocean are subject to dryer weather conditions.
(“Understanding the Indian Ocean Dipole.” YouTube, uploaded by Bureau of Meteorology, 5 July 2016, www.youtube.com/watch?v=J6hOVatamYs.)
Significant effects of the Indian Ocean Dipole anomalies are experienced mostly in Western and Southern Australia and in East Africa. A positive IOD event results in significantly drier conditions and less rainfall in southern and north-western Australia, thus increasing the chances of bushfires in the region. On the other hand, a positive IOD results in significantly increased rainfall during the East African Short Rains (EASR), occurring from October to December. This increased rainfall has resulted in frequent and increased flooding in East African countries. The effects of the Indian Ocean Dipole are felt in India especially when stronger positive IODs occur, leading to exceptionally heavy rainfall across the Indian subcontinent.
Climate change and the resulting climate variability is having a significant impact on the Indian Ocean Dipole and its positive and negative phases, leading to severe weather occurrences, such as megadroughts and deadly floods in countries surrounding the Indian Ocean. As the climate warms across the globe, extremely positive IOD events are increasing in frequency. In fact, four extreme positive events have occurred in the last sixty years, a significant increase in frequency compared to the mere six extreme events that have occurred in the preceding one-thousand years. Currently, such extreme events are occurring at a frequency of once every thirteen years, however, scientists postulate that in the coming future, these events could occur as close as once every six years.
Works Cited
“Understanding the Indian Ocean Dipole.” YouTube, uploaded by Bureau of Meteorology, 5 July 2016, www.youtube.com/watch?v=J6hOVatamYs.
“The Indian Ocean Dipole and Its Impact – | Prof TRACEY ROGERS.” YouTube, uploaded by Tracey Rogers UNSW Sydney, 18 Jan. 2019, www.youtube.com/watch?v=3Dk1r_lid18.
Dutton, Jan. “What Is the Indian Ocean Dipole?” World Climate Service, 2 Sept. 2021, www.worldclimateservice.com/2021/09/02/indian-ocean-dipole/. Accessed 3 May 2023.
“Indian Ocean Dipole: What Is It and Why Is It Linked to Floods and Bushfires?” BBC, 7 Dec. 2019, www.bbc.com/news/science-environment-50602971. Accessed 3 May 2023.
“Sea Level Key Indicators.” NASA, sealevel.jpl.nasa.gov/data/vital-signs/indian-ocean-dipole/. Accessed 3 May 2023.
Siliezar, Juan. “How Climate Change Impacts the Indian Ocean Dipole, Leading to Severe Droughts and Floods.” Brown, 4 Jan. 2023, www.brown.edu/news/2023-01-04/droughts-floods. Accessed 3 May 2023.
Hirons, L. and Turner, A. (2018) The impact of Indian Ocean mean-state biases in climate models on the representation of the East African short rains. Journal of Climate, 31 (16). pp. 6611-6631. ISSN 1520-0442 doi: https://doi.org/10.1175/JCLID-17-0804.1 Available at https://centaur.reading.ac.uk/76818/
Cai, Wenju, et al. “Guest Post: Why Climate Change Will Cause More ‘Strong’ Indian Ocean Dipole Events.” Carbon Brief: Clear on Climate, 30 Nov. 2020,
www.carbonbrief.org/guest-post-why-climate-change-will-cause-more-strong-indian-ocean-dipol e-events/. Accessed 3 May 2023.
India Ocean Project 