Matt Cawood in Queensland Country Life (Australia): What's common to Asian factories, Australian land clearing and the subtropical ridge? They have all been implicated in decreased rainfall over the Murray-Darling Basin. Climate researchers are grappling with the decade-long rainfall decline over the MDB, particularly in south-eastern Australia where lack of runoff has crippled irrigated agriculture and threatens urban water supplies.When your subject is something as vast as the planet's climate, a way to try and understand all the variables at work is to use computer simulations. Three separate computer modelling exercises have thrown up some interesting possibilities to explain the south-east's rainfall deficit.
The Bureau of Meterology's Dr Bertrand Timbal and colleagues have previously reported on a drought pattern linked to intensification of a band of high pressure called the subtropical ridge. They have now linked the ridge's behaviour to global warming.
As of May 2009, south-eastern Australia had recorded its driest 12-year period on record, with an annual average of 506mm since October 1996. Previously, the driest 12-year period was from 1935-1947, when the annual average was 511mm.
Dr Timbal's team identified a link between the two dry spells: they both occurred during a period when the subtropical ridge intensified. The high pressure band sits roughly between 30-35 degrees of latitude, in NSW defined by Wagga Wagga in the south and Walgett in the north. When it intensifies, Dr Timbal said, the ridge forces rain-bearing low pressure systems off the continent and out to sea….
The confluence of the Murray and Darling Rivers, shot by Peterdownunder, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 3.0 License
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