A national effort to save the Murray-Darling by returning 2750 gigalitres of water to the system is under way, but climate change could see roughly the same amount evaporate.
The extra water is needed to save ecosystems in the southern basin.
Top CSIRO scientist Francis Chiew says while it is a better scenario than not delivering the water at all, global heating means it is effectively giving with one hand and taking away with the other.
A reduction in flows means “Armageddon” in South Australia, Conservation council of South Australia chief executive Craig Wilkins warns, threatening wildlife and agriculture that depend on the water.
Chiew’s projections show increasing temperatures would see a 20% reduction in water flows, while a worst-case scenario would mean a “devastating” 40% reduction.
Chiew, a CSIRO research group leader, modelled the impacts of climate change on the Murray-Darling and found there have already been significant reductions.
“It’s been hotter … about 1.4C hotter over the last 100 years,” he said. “There’s more evaporation, and crops, the environment and people all use more water.
“We have also been seeing significant reductions in the stream flows, particularly in the southern basin.”
The Murray-Darling Basin Authority’s Dr Matthew Coleman said average annual inflows had decreased by 51% in the past 20 years, compared to the 100 years before it. “Less water moving through the system means less water for everyone,” he said.
Chiew said under climate change the flows would drop further. “The drier systems that we see will happen more frequently and will be more severe,” he said.
“For every degree of global warming you get a reduction of stream flow of about 10% in this region.”
Global warming of 2C would mean by 2060 there will be a 20% drop. The Paris Agreement set a target of limiting warming to 1.5C, but a United Nations report released on the eve of the Cop26 climate summit shows the world is on track for 2.7C.
“There’s a lot of uncertainty. Our worst-case scenario would be up to 40% (reduction in flows) in that region,” Chiew said. “Even at 20%, we’d have to make choices about what we do.”
“The plan is supposed to return the equivalent of 2750GL back to the environment … under the 20% scenario that’s probably equivalent to roughly the same number … but if we didn’t (get the 2750GL) it would be even worse.”
Wilkins said the impact of reduced flows were seen in the millennium drought.
During that drought, which ran from 2001 to 2009, residents and irrigators faced severe restrictions.
Aboriginal burial grounds were exposed, acid sulfate soils were exposed in the Lower Lakes, and low water levels caused parts of the riverbank to collapse.
SA Water looked at trucking in bottled water, parts of the Coorong became five times saltier than the sea, killing native plants and animals, and the Murray mouth closed, then had to be dredged around the clock to be kept open.
The mouth is still being dredged, 24 hours a day, 7 days a week.
‘Literally impossible’
Wilkins said the Murray was bordering on “whole system collapse” during the millenium drought, and if it faced those low flows again the “cancer” would spread, with salinity from the blocked Mouth flowing back up the river, threatening the Riverland food bowl, along with fish, turtle and bird species.
“If the lakes and the Coorong flip into acidic conditions, it’s Armageddon down there,” he said.
“The idea of having Australia’s greatest river with an open mouth becomes a fairytale, it becomes literally impossible.”
The desalination plant – built after the drought threatened water supplies – would help provide drinking water, he said, but agriculture and threatened species would be at risk.
Coleman said the basin plan itself was a “key climate adaptation tool” that limited the level of water extraction and helped build environmental resilience.
“Without water for the environment, the impact of climate change on the health of the basin would be more damaging,” he said, adding that governments, communities and industries were working together to face the climate challenge.
The millennium drought triggered the MDB Plan’s development, so the river system could be managed as a whole. Some estimated that 9000 gigalitres would need to be returned to, or kept in the system to keep it healthy. Bickering between the states drove that figure down to 2750 gigalitres. Eventually another 450 gigalitres was added specifically for SA’s environmental needs.
But New South Wales and Victoria are reluctant to promise that 450 gigalitres will ever flow downstream, arguing it will hurt farmers.
SA environment minister, David Speirs, said he would continue to pressure the other states to deliver “what’s been agreed, for the good of the river, our environment, and the communities that rely on it”.
“The most effective way to restore the health of the Murray-Darling Basin is through the full implementation of the basin plan. We are already seeing significant improvements across the Basin as a result of the water recovered to date, but there is still more work to do,” he said.
Federal water minister, Keith Pitt, said progress was being made, and that there were three years left on the plan to reach the water savings targets.
“There are challenges but it will come down to the commonwealth and basin states working cooperatively with a focus on what can be achieved rather than what they say they can’t do,” he said.
