22/06/2021

(AU SMH) Grim Climate Forecasts Point To Shrivelling Rivers In Northern NSW

Sydney Morning Herald - Peter Hannam

Dams will fill less frequently, farmers will face water cuts and rivers will cease flowing more often in areas across northern NSW as the climate warms and dries, putting at risk communities and wildlife alike.

The grim outlook is contained in a slew of draft regional water strategies for major river systems over the next 20 to 40 years, released by the Planning Department. It said it used “the best available evidence including new climate data and updated modelling”.

An aerial view of the southern Macquarie Marshes during the height of the recent drought. Image was taken in August 2019. Credit: Wolter Peeters

Dubbed “deliberately conservative...to give us an idea of the possible climate risks and allow us to begin planning to mitigate these risks if they arise”, the projections for eight major systems released so far point to shorter periods between droughts and less reliable flows when rivers run.

Under a worst-case scenario, for instance, annual volumes in the Peel River are projected to dive by 47 per cent and those in the rest of the Namoi River, into which it flows, would drop by 44 per cent.

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One consequence is the Barwon-Darling River, which now gets about one-quarter of its water from the Namoi system, will stop flowing more often. “Under a dry climate change scenario, there could be no end of system flows for 40 per cent of the time,” one of the reports said.

The stark warnings follow renewed alerts this month from the Murray-Darling Basin Authority Authority that flows into the Murray River in the basin’s south had dropped about 40 per cent in the past two decades compared with the average of the century before it.

The state’s findings also raise fresh concerns about the viability of the Berejiklian government’s plan to increase dam capacity or build new ones. For instance, while the government wants to raise the Wyangala Dam wall by 10 metres at a cost that has blown out to as much as $2.1 billion, the regional water strategy for the Lachlan River suggest flows in that system will dwindle.


“The probability of levels in Wyangala Dam decreasing below the critical drought trigger could increase from 7 per cent using the long-term paleoclimate records to 14 per cent using near future climate projections [and] to 43 per cent using long-term climate projections,” the report said.

Wyangala Dam when it all but dried out towards the end of the Millennium Drought in 2009. The NSW government wants to lift the dam wall in a project that may end up being triple the initial estimated cost. Credit: Kate Geraghty
Similarly, total flows along parts of the Gwydir River are forecast to drop by as much as 35 per cent. High flow events, which are important for trigger fish movement and spawning could shrink by a similar proportion.

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“It is possible for inflows into Copeton Dam [on the Gwydir River] to be half the volume of 27 gigalitres over 24 months” seen during the recent drought, the report said.

Upper House independent MP Justin Field said the reports should prompt the government to rethink its approach to managing rivers.

“Water Minister Melinda Pavey spectacularly fails to provide any meaningful plan for dealing with the impacts of this decrease in water availability, instead offering up the same discredited strategies of more dam building and turning our coastal rivers inland,” Mr Field said.

“These climate realities also raise yet more concerns about the government’s plan to licence billions of litres of water for floodplain harvesting in the northern Murray-Darling Basin,” he said. “Issuing these licences based on historical take when we know that water simply won’t be there in the future is a recipe for disaster.”

A spokeswoman for Ms Pavey said farmers and regional communities were on the frontline of climate extremes.“This is the first time any NSW government has embarked on long-term planning for water security and drought resilience.”

Menindee Lakes in far-western NSW have been filling for the first time in five years. Future climate predictions suggest the Barwon-Darling River which feeds them may cease to flow about 40 per cent of the time. Credit: Wolter Peeters
“The 12 Regional Water Strategies will consider a full range of options to address current and future water challenges, including infrastructure options, water recycling and reuse, and improved water efficiency, to secure water during extreme events and... the toughest droughts,” she said.

Matt Colloff, a former CSIRO scientist now at the Australian National University, said different NSW agencies were producing varying outlooks.

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For instance, another part of the Planning Department predicted in a hydrology report that “across much of NSW, surface runoff is projected to increase in both the near and far future”.

“Largest increases are evident in the central west through to the northern tablelands. Large reductions in surface runoff are projected in both the near and far future for alpine areas in the south of the state,” it said.

Dr Colloff said the new batch of reports “present no data on range, variation or uncertainty, only the worst case scenario”.

”Call me a cynic, but this says to me they are intended to carry a message that ‘we can’t implement the [Murray-Darling] Basin Plan because of climate change,‘” he said. “And ‘because of climate change, irrigators in the Northern Basin should be allowed to continue with floodplain harvesting’.“

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