Four of the world's great river systems, including the Murray-Darling Basin, are suffering significantly from reduced water flows. A new report shows that water extraction has the biggest impact on the health of a river.
One of the report's authors, Dr Jamie Pittock, told Crikey
: "While climate change will aggravate changes in flows in river systems, current high levels of water extractions remain the principal contributor to reduced flows and degradation of these rivers."
The paper, Global insights into water resources, climate change and governance
, was published yesterday in Nature Climate Change.
The study was conducted by ANU researchers Professor Quentin Grafton, Dr Jamie Pittock, Professor Tom Kompas, Daniel Connell and other colleagues from around the world, who looked at the health of the US Colorado River, the South African Orange River, the Chinese Yellow River and the Murray-Darling River system.
"The ecosystems of rivers subject to large extractions around the world are degrading rapidly. The impacts are many," said Pittock. "River and estuarine fisheries and also floodplain forests are being lost due to changes in the volume, quality and timing of water flows.
"Dams are preventing migration of fish and other wildlife, as well as blocking flows of sediments and nutrients downstream. Most impacted are the lower reaches of rivers and estuaries that suffer from saline intrusion, and in the case of deltas, extensive loss of rich farm lands and wildlife habitats.
"Water quality of the impacted rivers is degrading with increases in salinity and nutrient levels as well as acidification in some areas, due to loss of flushing flows, and in some cases, wetlands vegetation."
Pittock says their study showed that of the river systems the Murray-Darling Basin and the Yellow River were the most favourable managed. The Yellow River is the first to have had significant flows restored to the sea after over-exploitation meant it had dried up.
"Australia has experimented with a number policies for better managing rivers more so than other countries," said Pittock. "Examples include more rigorous water accounting, capping water extractions and establishing a trading system for water that enables entitlements to be easily traded up to more socially and economically valuable uses. Our water entitlements that are based on shares of the available resource are a long-standing hedge against variable water availability. The establishment of the Commonwealth Environmental Water Holder and potentially the Basin Plan are other examples."
Going beyond the paper, Pittock critiques the Murray-Darling Basin Plan, saying it provides a structure that could lead the Basin to a sustainable future. "The plan puts in place key institutions that could put the nasin on a sustainable path. In particular the commitments to return more water to the rivers, to share available water in any year more equitably between the rivers and entitlement holders, and the promises to periodically review and upgrade the plans are essential for sustainability," he said.
Despite this, in his view the plan still doesn't go far enough. While Australia has taken some important steps, more needs to be done.
"Detracting from this are too little re-allocation of water to meet environmental targets; the increase in groundwater take; failure to make provisions for losses due to climate change; an excessive period for implementation -- stretching to 2024, and an expensive and risky reliance on engineering works for farm water supplies and wetlands to recover water," he said. "The proof is in the birds and the fish and the riverine forests. Yet their health remains parlous."
Pittock says this matches a global reality, where more action needs to be taken to fix our rivers. "Globally water extractions are increasing markedly. More and more rivers are no longer reaching the sea," he said. "Stronger action is needed to ensure that in dry times, the rivers get a fair share of the available water."
The paper, released yesterday, was conducted with researchers from the University of Queensland, the University of Canberra and international collaborators from universities in the USA, China, and South Africa.