No more normal: Australia’s Big Wet and Long Term Dry
By Sou from Bundangawoolaran
7 February 2012 Today the Bureau of Meteorology issued a Special Climate Statement: Australia’s wettest two year period on record; 2010-2011. The statement speaks for itself. There are towns this year, as there were last year, having record floods. Following the ‘Big Dry’ it would seem that Australia is no longer having extremes interspersed with ‘normal’ periods, but is swinging from one extreme to another – with a long term underlying drying trend across much of the country. There is no ‘normal’ any more. Long-term below average rainfall
This is not the only thing as the Bureau of Meteorology statement points out:As wet as it has been, the longer term averages still show much of Australia to have received below-average rainfall. Dry conditions have persisted across both southwestern and southeastern Australia in recent decades. The drought conditions can be characterised in a number of different ways. Perhaps the most statistically significant rainfall changes that have occurred are a 10-20% reduction in autumn and winter rainfall across the southeast since 1996, and a similar decline in winter rainfall across the southwest since around 1970. The April to November period is the main rainfall and runoff season for both these parts of Australia, with less rainfall falling in summer. Special Climate Statement 9, released in October 2006, reported on an exceptionally dry decade in parts of southern and eastern Australia.
During the period of declining autumn and winter rainfall, there has also been an absence of wet years across the south-east and south-west. This has exacerbated drought conditions in these regions. The substantial decline in autumn and winter rainfall in recent decades is largely associated with a reduction in rainfall from cold fronts/low pressure systems and an increase in mean surface pressure, associated with an increase in the number of high pressure systems. […]
