Monday, May 20, 2019
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Australia, the Indian Ocean Dipole and El Nino

After a winter of drought, Australia faces failing summer rains too as the oceans adopt an unfavourable pattern.

El Nino

You may well have heard of El Nino, but how about the Indian Nino?

El Nino (ENSO) is the movement of warm water across the equatorial Pacific, from the Philippines Sea to the west coast of South America.

The Indian Nino, better known scientifically as the Indian Ocean Dipole (IOD), is the movement of warm water from Sumatra, across the equatorial Indian Ocean to East Africa.

These are both major events because they move the usual areas of expected rain by thousands of kilometres. This happens because warm water produces rising moist air which forms rain clouds.

According to the Australian Bureau of Meteorology (BoM), the pattern of sea surface temperatures in the Indian Ocean has reflected a positive IOD for the last two months.

As of Wednesday, this was long enough for it to be officially declared as a positive IOD event.

In the Pacific Ocean, the chance of an El Nino event developing soon and lasting over the northern hemisphere winter is over 70 percent, according to the calculations done by NOAA and BoM. Australia takes a particular interest in these phenomena because both have a significant effect on the country's rainfall pattern.

The IOD is one of the key drivers of Australia's climate and can have a significant effect on agriculture. This is because events generally coincide with the winter crop growing season. A positive IOD during spring increases the chance of below average rainfall for southern and central Australia.

El Nino is typically associated with reduced rainfall in northern and eastern Australia. Reduced cloudiness allows higher temperatures by both day and night and greater evaporation of open water sources and soil moisture.

El Nino effects in Australia over summer include higher fire risk, greater chance of heatwaves and fewer tropical cyclones.

In the worst-case scenario, and suggested by a study published only this year, a positive IOD can increase the effects of ENSO. This would worsen Australia's current drought conditions, presently affecting New South Wales the most.

Despite this apparent prediction of doom, according to the BoM, model outlooks suggest the positive IOD will start to decay during November. IOD events typically have little influence on Australian climate from December to April.

The developing El Nino is a different matter.

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