Indian Ocean Dipole
Published on 02 Feb 2025
The Indian Ocean Dipole (IOD) is a climate pattern that describes the unusual warming or cooling of the sea surface temperatures in the western Indian Ocean (Arabian Sea) compared to those in the eastern Indian Ocean (Bay of Bengal). IOD has two main faces;
Positive IOD: During a positive IOD event, sea surface temperatures in the western Indian Ocean (Arabian Sea) are warmer than normal, while those in the eastern Indian Ocean (Bay of Bengal) are cooler than normal. This temperature difference creates a dipole pattern, with warmer waters in the west and cooler waters in the east. Generally, this means there is less moisture than normal in the atmosphere to the northwest of Australia.
Negative IOD: During negative IOD event, the sea surface temperatures in the western Indian Ocean (Arabian Sea) are cooler than normal, while those in the eastern Indian Ocean (Bay of Bengal) are warmer than normal. This creates a reverse dipole pattern, with cooler waters in the west and warmer waters in the east.
Similarity to ENSO: The IOD is similar to El Niño and La Niña, which are climate patterns that occur in the Pacific Ocean. However, the IOD is specific to the Indian Ocean and has its own unique characteristics.
Impact of IOD on climate
On rainfall and monsoon: Positive IOD leads to increased rainfall in the Indian sub-continent positively affecting monsoons and negative IOD brings decreased rainfall and obstructs progression of monsoon over India.
Drought: Negative IOD increases water scarcity and drought like conditions and positive IOD reduces drought by bringing in more moisture and rain.
Cyclones: positive IOD results in more cyclones than usual in Arabian Sea. Negative IOD results in stronger than usual formation of cyclones in the Bay of Bengal region.
Flood: Positive Indian Ocean Dipole (IOD) can lead to increased rainfall in certain regions, intensifying the monsoon and causing floods. Warmer sea surface temperatures in the western Indian Ocean contribute to enhanced convective activity, impacting agriculture and increasing the risk of flooding.
Bushfire: Negative Indian Ocean Dipole (IOD), with cooler sea surface temperatures, leads to reduced rainfall. This dry condition heightens bushfire risks by drying vegetation and increasing susceptibility to wildfires.
