All the wrong stars aligned for perfect storms
THE strong La Nina pattern taking moisture to north-eastern Australia has been exaggerated by record high ocean temperatures, a combination not seen on this scale since the deadly Brisbane flood of 1974 which claimed at least 14 lives.
And while Queensland's already saturated catchments are lashed with heavy rain, south-western Western Australia is experiencing an extreme dry - and bushfires.
''Australia has been known for more than 100 years as a land of droughts and flooding rains, but what climate change means is Australia becomes a land of more droughts and worse flooding rains,'' David Karoly, from Melbourne University's school of earth sciences, said.
Professor Karoly stressed individual events could not be attributed to climate change. But the wild extremes being experienced by the continent were in keeping with scientists' forecasts of more flooding associated with increased heavy rain and more droughts as a result of high temperatures and more evaporation.
''On some measures it's the strongest La Nina in recorded history … [but] we also have record-high ocean temperatures in northern Australia which means more moisture evaporating into the air,'' he said. ''And that means lots of heavy rain.''
In Queensland's case, the recent rain fell on already saturated catchments, making the run-off rate high. In the weeks from November 28 to December 31, total rainfall exceeded 300 millimetres over most of the eastern half of the sunshine state.
''In Victoria we had heavy rainfall but the run-off hasn't been as high because after 10 years of drought the ground wasn't as saturated,'' he said.
A Bureau of Meteorology special climate statement issued this week said that last month was the wettest December on record for Queensland and for eastern Australia as a whole.
This followed an unusually wet Australian spring - the wettest on record for Queensland and NSW.
A visiting fellow at the Australian National University's integrated catchment assessment and management centre, Tony Weber, said the catchments had reached saturation levels and there did not need to be record rain falls to result in ''extreme run-off events''.
He said it would take several weeks before the catchments were sufficiently dry to lift the threat of further flooding - and even then, that would occur only if major rainfall eased.
La Nina phases recur every three to five years and last about 12 months. Professor Karoly said this cycle began earlier than usual and could last until May.
The last La Nina was in 2007 but it did not coincide with such warm oceans.