Australia's highly variable climate is influenced by the broad patterns in the oceans around it and the atmosphere above it. We call these patterns our climate drivers. The most significant climate driver in the Indian Ocean is the Indian Ocean Dipole, often called the IOD. The IOD refers to the year-to-year changes of tropical sea temperatures in the western and eastern Indian Ocean. These changes can alter the weather patterns that affect Australia's rainfall.
The IOD varies between three phases: positive, neutral and negative. On average each phase occurs about every 3–5 years. Positive or negative IOD phases usually begin in autumn or winter, and return to neutral around the end of spring when the northern Australian monsoon arrives. During a neutral phase, water from the Pacific flows between the islands of Indonesia, keeping seas to Australia's northwest warm. Air rises above this area and falls over the western half of the basin, blowing westerly winds along the equator. Temperatures are close to normal across the tropical Indian Ocean and the IOD has little influence on our climate.
During a negative phase westerly winds intensify, allowing warmer waters to concentrate near Australia. These stronger winds also mean it's harder for cool water to rise up from the deep near Indonesia. As these warmer waters move east, the clouds follow, favouring weather patterns that ultimately bring rain to southern Australia.
A positive IOD phase has the reverse temperature pattern in the Indian Ocean, and the opposite effect on Australia's climate. The westerly winds weaken and sometimes easterly winds form, allowing warm water to shift towards Africa. South of Indonesia, these changes in the winds allow cool water to rise up from the ocean depths. With cooler waters and descending air in the eastern Indian Ocean, less cloud forms. This changes the path of weather systems coming from Australia's west, often meaning less rain over central and southeast areas.
Often, but not always, a positive IOD coincides with the drying influence of the El Niño in the Pacific, both drawing rainfall away from Australia. For southeast Australia this can cause the failure of critical winter-spring rains and prime the land for severe summer fire seasons. For instance, 1982, the driest year on record for the region, was both a positive IOD and El Niño, and was followed by the devastating Ash Wednesday bushfires.
Likewise, a negative IOD can often occur during La Niña, both pushing more rain towards Australia. If both are strong, Australia can experience significant rainfall and widespread flooding. We saw this in two of the three wettest years on record for Australia, 1974 and 2010. Both years brought costly and deadly flooding to many areas. The Indian Ocean Dipole plays an important role in driving Australia's climate. No two Indian Ocean Dipole events and no two set of impacts are exactly the same. Understanding this key Australian climate driver can help you make smarter decisions.
The IOD varies between three phases: positive, neutral and negative. On average each phase occurs about every 3–5 years. Positive or negative IOD phases usually begin in autumn or winter, and return to neutral around the end of spring when the northern Australian monsoon arrives. During a neutral phase, water from the Pacific flows between the islands of Indonesia, keeping seas to Australia's northwest warm. Air rises above this area and falls over the western half of the basin, blowing westerly winds along the equator. Temperatures are close to normal across the tropical Indian Ocean and the IOD has little influence on our climate.
During a negative phase westerly winds intensify, allowing warmer waters to concentrate near Australia. These stronger winds also mean it's harder for cool water to rise up from the deep near Indonesia. As these warmer waters move east, the clouds follow, favouring weather patterns that ultimately bring rain to southern Australia.
A positive IOD phase has the reverse temperature pattern in the Indian Ocean, and the opposite effect on Australia's climate. The westerly winds weaken and sometimes easterly winds form, allowing warm water to shift towards Africa. South of Indonesia, these changes in the winds allow cool water to rise up from the ocean depths. With cooler waters and descending air in the eastern Indian Ocean, less cloud forms. This changes the path of weather systems coming from Australia's west, often meaning less rain over central and southeast areas.
Often, but not always, a positive IOD coincides with the drying influence of the El Niño in the Pacific, both drawing rainfall away from Australia. For southeast Australia this can cause the failure of critical winter-spring rains and prime the land for severe summer fire seasons. For instance, 1982, the driest year on record for the region, was both a positive IOD and El Niño, and was followed by the devastating Ash Wednesday bushfires.
Likewise, a negative IOD can often occur during La Niña, both pushing more rain towards Australia. If both are strong, Australia can experience significant rainfall and widespread flooding. We saw this in two of the three wettest years on record for Australia, 1974 and 2010. Both years brought costly and deadly flooding to many areas. The Indian Ocean Dipole plays an important role in driving Australia's climate. No two Indian Ocean Dipole events and no two set of impacts are exactly the same. Understanding this key Australian climate driver can help you make smarter decisions.
Understanding the Indian Ocean Dipole (IOD)
12 March 2025
The IOD is a driver of Australia's climate. Learn how it can alter weather patterns that affect rainfall in central and southern Australia.