Wetter than normal weather expected for Geelong, as Bureau of Meteorology reports negative Indian Ocean dipole

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Dr Ailie Gallant explains the science behind the Indian Ocean Dipole. Also, what could this mean for Geelong’s rainfall in the coming months?

The Bureau of Meteorology (BoM) has announced that a negative Indian Ocean Dipole (IOD) is underway, which could impact Geelong’s rainfall in the coming months.

In recent decades, parts of southern and eastern Australia have become much drier.

Some regions have experienced as much as 20% less precipitation during their cooler months between April and October.

But despite these long-term drying trends, precipitation is highly variable and can fluctuate from year to year.

BoM data suggests Geelong winter and spring 2021 may be wetter than normal.

This is due to what is called an “Indian Ocean negative dipole”, or negative IOD for short.

What is a negative IOD?

The IOD refers to the annual changes in temperature in the Indian Ocean.

This year, the waters of the Indian Ocean off Indonesia – not too far from the northern coast of Western Australia – are warmer than normal.

Meanwhile, the waters in the western part of the Indian Ocean near East Africa are cooler than normal.

Scientists refer to this particular swing in ocean temperatures as a Negative IOD.

During such an event, the amount of evaporation near Indonesia increases.

So when conditions are right, this humid air moves over Australia, bringing rain to the south and southeast of the country.

This year’s negative IOD event means large parts of Australia are likely to experience above average precipitation over the next three months, including Geelong.

How does climate change affect these models?

Recent research from Australian National University suggests that negative phases of IOD may become less frequent if global temperatures continue to rise.

In contrast, positive IOD phases – which create dry conditions – are likely to become more common.

This could disrupt the natural cycle of wet and dry years, adding to the risk of drought in Australia.

The last positive IOD occurred in 2019 and was linked to the dry conditions that preceded the catastrophic black summer bushfires in Australia.

Listen to your local community:

Do you want more information on the evolution of your climate? Discover the last article in this series.

Dr Ailie Gallant is a climatologist and senior lecturer at Monash University.

This column is part of a collaboration between Monash University and News Corp to provide hyperlocal weather and climate information.


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