{News}090205! Indian Ocean is drought culprit
Indian Ocean is drought culprit
Ben Cubby, Environment ReporterFebruary 5, 2009
THE main cause of our droughts and flooding rains has been traced to the waters of the Indian Ocean, according to a new report from the University of NSW which could overturn decades of weather research.
The study shows that the cycle of El Nino and La Nina events, which have long been thought to play a major role in south-east Australia's weather patterns, are in fact less important than the Indian Ocean.
It is likely to have major implications for predicting rainfall in the Murray-Darling region - still in the grip of the most severe drought on record - by giving farmers tip-offs about rainfall increases six months in advance.
The current Indian Ocean warming pattern is unprecedented and probably related to climate change, researchers say.
The report found that a phenomenon known as the Indian Ocean dipole plays a dominant role in determining temperature and rainfall in south-east Australia.
It examined data on changes in the distribution of warm and cool water and found a direct correlation between dipole events and the current drought, as well as the devastating centenary drought between 1895 and 1902 and the so-called World War II drought of 1937-45.
"There really is that opportunity to improve seasonal forecasting and seasonal predictions due to these findings, because the Indian Ocean dipole is predictable several months in advance," said the lead author, Dr Caroline Ummenhofer.
During a "negative" Indian Ocean dipole, cooler winds carry moisture in south-eastern Australia. During a "positive" dipole, warmer, dryer winds limit rainfall and contribute to high temperatures. In the past three years there have been successive positive cycles.
"This is something new. This has never, in the historical record, happened before," Dr Ummenhofer said. "So there are some indications that positive Indian Ocean dipole events are becoming more frequent and negative events are becoming less frequent."
The dominant role of the Indian Ocean explains why the La Nina event, which usually brings more rain, failed to break the drought when it last occurred in 2007.
"If these Indian Ocean dipole events do follow the trend [of more positive and fewer negative events], this is a terrible piece of information for the Murray-Darling Basin," said Professor Matthew England, co-director of the Climate Change Research Centre.
The Bureau of Meteorology said the findings, from the University of NSW with help from researchers at the CSIRO and the University of Tasmania, confirmed a growing belief in the Indian Ocean's significant role in determining the weather in south-east Australia.
In the past fortnight, the bureau said many temperature records had not so much been broken as smashed, as the southern states endured the heatwave. "Normally you see records broken by a fraction, but in Tasmania for example, the record at one station went by nearly 2 degrees," said Dr David Jones, head of the bureau's National Climate Centre.
The Murray-Darling Basin Authority's quarterly update yesterday showed the drought there is worsening. Toxic algae blooms are expected, water storage is down by two-thirds and decent rain is months away.
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