By Bridie Smith
THE strong La Nina pattern currently transporting moisture to north-eastern Australia has been exaggerated further 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, the south-west of Western Australia is experiencing an extreme dry – and bushfires.
”Australia has been known for more than a hundred 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,” said David Karoly from Melbourne University’s school of earth sciences.
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Professor Karoly stressed individual events could not be attributed to climate change. However, he said the wild extremes being experienced on the continent were in keeping with scientists’ forecasts of more flooding associated with increased heavy rain events 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, which had been soaked by heavy rains, 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, while we had heavy rainfall, 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 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 didn’t need to be record rainfalls 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 only occur if significant rainfall eased.
La Nina phases recur every three to five years, lasting about 12 months. Professor Karoly said the current cycle began earlier than usual and could last until May. The last La Nina event was in 2007.
Source: www.smh.com.au
