Wet winters a thing of the past

03 Oct, 2012 05:20 AM
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22
 

With spring in full swing, much of south-eastern Australia hasn't looked this green for years - 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.

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"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.

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READER COMMENTS

Ted O'Brien.
3/10/2012 11:33:23 AM

'Twas ever so. Have you checked the sea level lately? It's heading down, not up.
David Harrison
3/10/2012 6:05:18 PM

Once again we see the use of limited data collection to foretell the future. I am not against science, modelling or facts. But please, don't present an argument for long term scenarios with short term fact collection. At best, it is a guess, at worst it is the pedalling of misinformation.
Ian Mott
4/10/2012 6:54:46 AM

Yawn. More extrapolation from cherry picked data.
hungry sheep
4/10/2012 8:59:23 AM

More rubbish.....many parts of southern Australia have been underwater this winter...the proponents of this information clearly need to get out more...
nico
4/10/2012 9:00:36 AM

Please provide (credible) evidence, T O'B, for your extraordinary assertion that sea levels are going down. See: http://sealevel.colorado.edu/
Dirty Harry
4/10/2012 9:30:41 AM

Nico, my questions on cooling ? And why is Teds assertion so extraordinary ? Sea Levels go up and down all the time. Have been for millions of years, a 12 year old knows that.
Bill Pounder
4/10/2012 10:47:35 AM

" We find that there is a significant oscillation with a period around 60-years in the majority of the tide gauges examined during the 20th Century, and that it appears in every ocean basin." http://www.agu.org/pubs/crossref/ 2012/2012GL052885.shtml "..sea levels ~6,000 years BP were one to two metres higher than today.." http://www.warwickhughes.com/blog /?cat=11 “Children just aren’t going to know what snow is,” Dr David Viner, CRU, 20/3/00 and "Children just won’t know what pumpkins are." as early Sept 2012 snow, Alberta, Canada wipes out Halloween crops.
Craw
4/10/2012 2:51:48 PM

I'm not sure how the figures were analysed for this report. But by Dr Whetton's definition we definitely had a 'wet' winter in 2010, preceeded by a 'wet' Feb/March 2010, followed by a 'very wet' harvest and summer / early autumn 10/11, and another 'wet' harvest and autumn 11/12. The BOM site also shows the number of 'wet' seasons since Spring 2006, for all states and the whole country. There are quite a few 'wet' ones despite the dry decade of the noughties. I wouldn't mind even an 'average' spring this year though - given that grain prices are so strong! I'm in SWSlopes NSW.
nico
5/10/2012 7:19:36 AM

As Mounder must be aware, sea level rise is not a simple linear trend. The 60 year oscillation suggested by Chambers is interesting, as is the El Nino effect (see Chambers: http://www.agu.org/pubs/crossref/ 2012/2012GL053055.shtml). What matters is that - while the graph may be a zigzag - the trend is upwards. Just as the temperature trend is upwards. Please check the science for yourself (but avoid dodgy blogs and sensational journalists.)
Percy
6/10/2012 10:55:34 AM

Don't you just love the way these supposedly learned people use selective sciantific information to talk down the weather? I presume that is simply to try to justify the carbon tax we are leading the world on while other nations and volcanos emit far more than Australia does (unless you use the per person rate which is pretty stupid for a huge country with a small population). No two years are the same and never will be in a universe that is always changing.
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