Wet winters a thing of the past

With spring in full swing, much of south-eastern Australia hasn't looked this green for years. Sydney's dam levels are well above 90 per cent while reservoirs serving Melbourne slosh over the 80 per cent mark.

But enjoy nature's bounty while it lasts. Much of the country's south-east recorded another below-average rainfall result for the key April to September period, and the Bureau of Meteorology is tipping warmer and drier-than-normal weather for the rest of 2012.

Across southern Australia, September's rainfall came in at 15.6 millimetres – more than 40 per cent below the 1961 to 1990 average, said Karl Braganza, manager of climate monitoring for the Bureau of Meteorology. Nationally, the previous month was even drier – the sixth-driest August in 110 years of records.

"It really was dry through most of South Australia into western NSW, much of Victoria and large parts of WA," Dr Braganza said, referring to the six-month stretch.

"It's a pattern of drying that we have now observed for more than 15 years over in the east, and for more than 30 years out in the west.

"It has been amazing to see that drying pattern quickly re-establish itself from mid-autumn this year, pretty much as soon as the influence of La Nina diminished," he said, referring to the weather pattern that typically brings heavier-than-usual rainfall across eastern mainland states.

Victorians living south of the Great Divide enjoyed relatively good rains in recent months. But the lush pastures and healthy river flows over the wider region owe much to back-to-back wet summers that raised deep-soil moisture levels, Dr Braganza said. "We still have water in the bank."

However, disappointing rains over the autumn, winter and spring in Victoria's Wimmera and Mallee mean those deposits are rapidly being drawn down.

"There has been a general drying, particularly across the grain-growing areas, pretty well across NSW and Victoria," said Peter Tuohey, a fifth-generation farmer and current president of the Victorian Farmers Federation.

Grain-growers in the state's north-west "are certainly looking for rain" Mr Tuohey said, as his tractor sprayed weeds on one of his paddocks near Pyramid Hill.

"It's certainly a very critical stage - the crops have just been hanging on and unless they get some rain soon they're going to struggle to finish up."

Cool and dry

Scientists say Australian winters are becoming drier with man-made actions - particularly the burning of fossil fuels - to blame.

Penny Whetton, a senior principal research scientist developing climate change projections at the CSIRO, said modelling of the climate's response to increased greenhouse gases in the atmosphere points to the drying in the cool seasons across Australia.

"It's in southern Australia where (the drying trend) is most important because quite a lot of our rain comes in the cool season," Dr Whetton said.

"What we see in recent years is drier conditions, particularly in the south-west of Western Australia, and more recently stretching over to the southeast."

Indeed, while Australians are accustomed to battling a variable climate, those fluctuations now rarely include wet winters. The last very wet winter - with rainfall greater than 50 per cent above the seasonal averager - in the nation's south-east was 1991, while south-western WA hasn't had one since 1965.

Dr Braganza said summer-like weather patterns are becoming more common during winter. "We've got a trend of more high-pressure systems over southern Australia," he said, with the result that rain bands are pushed south of the continent.

"Potentially the models have been underestimating these rainfall shifts."

Dr Whetton said that while climate models vary in their predictions of longer-term trends for southern Australia, one outcome seems increasingly unlikely. The scenarios "are a future where both summer and winter dry out or we might have a scenario where summer gets wetter and winter gets drier". "We're not likely to get a scenario where winter gets wetter," she said.

The story Wet winters a thing of the past first appeared on The Sydney Morning Herald.

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