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Looming El Nino sets up gloomy forecast

News analysis South-east Australians can expect little relief from below average rainfall according to climate experts.

The latest forecast from the National Climate Centre in Melbourne says the chances of an El Niño weather pattern developing are twice as strong as normal.

Ans in a potential double-blow, a weather system in the Indian Ocean that research shows has a strong correlation with severe bushfires in the region may also be emerging.

Another year of poor rainfall could also be devastating for the already stressed Murray-Darling river basin.

Telltale signs

Dr David Jones, head of climate analysis at the National Climate Centre says modelling shows the precursors to an El Niño are all tracking in the right direction.

During a typical El Niño event the surface temperature of the Pacific's equatorial waters are at least 0.8°C warmer than normal, he says. They are now half a degree warmer than average.

Jones also points to weakening trade winds and a drop in the Southern Oscillation Index, which tracks air pressure differences between Tahiti and Darwin, as further evidence El Niño is on its way.

He says there is also evidence that the Indian Ocean Dipole (IOD), which plays a strong role in delivering rainfall to Australia, is trending positive.

In its negative phase, the IOD brings cool water to the west coast of Australia and warm water to the north, resulting in increased evaporation into the atmosphere and rain-bearing air sweeping over the continent.

A positive IOD occurs when the western side of the Indian Ocean off Africa and India is warmer than the eastern waters near Sumatra.

As a result, less rainfall travels to Australia, in particular Victoria.

Jones says the indications are Victoria will get no relief from 13 years of drought, with 1996 the last year the state recorded above-average rainfall.

"Soil moisture across Victoria is at record-breaking lows," he says. "It's not been this dry for a very long time."

Stressful time

Professor Matthew England, director of the Climate Change Research Centre at the University of New South Wales says the combination of an El Niño and positive IOD will put great stress on the south-east corner of Australia.

"If a full-blown positive Indian Ocean dipole materialises and that is accompanied by an El Niño this could give rise to a very dry winter and spring over south-eastern Australia," he says.

England says another year of below average rainfall would not only increase fire risk in Victoria, it also increases the "challenge of keeping the Murray-Daring Basin viable".

"It puts stress on the ecosystem, it puts stress on the farming community."

However England says the Indian Ocean Dipole does not peak until the spring months of September, October and November.

"It would be very early for the Indian Ocean Dipole to be showing its true colours for the coming seasons," he says.

Dr Tim Cowan, a research with CSIRO Marine and Atmosphere Research, says in terms of rainfall an El Niño "wouldn't be the best thing to get right now".

Cowan and colleague Dr Wenju Cai, also of the CSIRO, have found the combination of an El Niño and positive IOD increases the risk of a major bushfire season developing.

"El Niño on its own doesn't increase the risk, but the IOD tends to push the climatic conditions into a higher bushfire risk."

In their most recent study they found 11 of 16 major bushfires in Victoria since 1950 had been preceded by a positive IOD.

Degree of impact

Cowan supports England's view that it is too early to begin making predictions about the IOD.

However their research shows under climate change there is a trend toward more positive IODs.

Jones says although the bureau has improved its predictive capacity, there is no way of telling how the El Niño will impact on Australia.

"The 2006 El Niño was reasonably weak yet it had a severe impact … across southern Australia and in the Murray Darling Basin," he says.

England agrees and says although the ability to predict these events is improving, it is harder to know their impact.

"The atmosphere has a degree of chaos to it. It's a very complex system to forecast … we've all heard the anecdote of the butterfly wing that flaps over South America creating a cyclone north of Australia. The atmosphere has a capacity to surprise and not all El Niños are the same."