Perth’s drinking water supplies from dams will run out by the end of next summer even with decent rainfall, according to predictions by the Centre for Water Research.
By then, Perth and the South-West would become solely reliant on water supplied from the already stressed Gnangara Mound aquifer and the Kwinana desalination plant, director Jorg Imberger said.
Even using an optimistic calculation that 35 gigalitres (35 billion litres) of rainwater would flow into the city’s dams - far greater than the 13 gigalitres last year - the dams would run dry.
“(Even) given recycled water, less water use, pumping the surface aquifer at Gnangara Mound a little bit more and hoping for rain, we’ll basically have no water left at the end of summer 2012,” Professor Imberger said.
The comments confer with the national Climate Commissioner’s first report released yesterday, which warns that water availability will be at great risk before the end of the century due to changing rainfall patterns.
WA’s South-West region was already “drying out” and all projections showed no improvement, the report by Professor Will Steffen said.
“Rainfall is the main driver of run-off, which is the direct link to water availability,” the report says.
“Hydrological modelling indicates that water availability will likely decline in south-west Western Australia.”
Perth’s dam capacity is already below 25 per cent and only 10 per cent of that is drinkable.
WA Water Commission figures show the average amount of rainfall flowing into the dams has dramatically declined since 1974:
- 1911 - 1974 - 338 gigalitres
- 1974 - 2000 - 117 gigalitres
- 2001 - 2005 - 92.4 gigalitres
- 2006 - 2010 - 57.7 gigalitres
“It’s raining less but the reduction into reservoirs has reduced even more because the vegetation is sucking up the rest (due to deforestation),” Professor Imberger said.
“Between 30-40 per cent of that reduction is due to climate change. The remainder is down to land clearing - trees are not (there to) recycle water the way they used to be.”
But a Water Corporation spokesman said it was too early too predict how much water would be left in the dams by early next year.
He said over the past 10 years the dams had averaged 100 billion litres of water per year, although last year only 13 billion litres flowed.
Rainfall flows into the dams had been getting later and later each year but it already started this year.
According to the Bureau of Meteorology, the Perth metropolitan area recorded only 59 per cent of its average annual rainfall last year.
A record hot summer brought no relief and so far this year, less than 50 millimetres of rain has fallen in Perth.
Professor Imberger said the state government’s only option to avoid running out of drinking water was to immediately bring other sources online.
That included expanding use of the Yarragadee aquifer in the South-West, doubling capacity of the second desalination plant at Binningup - due to come online by the end of the year to provide 45 gigalitres of water - to 100 gigalitres, and improving water recycling.
“Of this really serious situation nobody seems to be doing something about it,” Professor Imberger said. “Maybe they’re just hoping all this is going to go away.”
Several WA water experts have recommended tapping further into the Yarragadee aquifer to ease pressure on Gnangara Mound, which stretches from Gingin, north of Perth, to the Swan River.
The south-west aquifer stores about 1000 gigalitres and could provide three times as much drinking water as the Kwinana desalination plant, according to Professor Imberger, but the government has so far resisted using it due to opposition from locals.
Professor Imberger said planting thousands of new trees in south-west WA also would help boost future rainfalls.
The state government did not respond to inquiries about how it was managing Perth’s drinking water supply.
