Modelling projects deepening aridity will reshape Australia’s inland rivers within 50 years

Australia’s inland rivers could be dramatically reshaped within the next half-century as aridity increases, even under a relatively moderate climate change scenario, according to modelling published in Scientific Reports by Macquarie University’s Wetlands in Drylands team.

The researchers, led by Zacchary Larkin and Tim Ralph, modelled how a drying climate would affect river systems across a continent where 78 per cent of the landmass is already classified as dryland. Their modelling indicates the arid zone that encompasses true desert will expand into a large area of the Murray–Darling Basin and almost entirely engulf the Lake Eyre Basin.

Humid and dry sub‑humid fringes around the Great Dividing Range and coastal areas are also likely to contract, a pattern that could reduce rainfall and runoff in the headwaters on the range’s western slopes where many inland rivers begin. Of the 29 rivers analysed, 23 are projected to shift into another river type.

The Lachlan and Macquarie rivers, for example, are expected to come to resemble present‑day central Australian rivers—persisting as disconnected channels and waterholes for long periods. Internationally significant wetlands including the Great Cumbung Swamp and Macquarie Marshes are predicted to be impacted, with inundation much less frequent and major consequences for the vegetation and wildlife they support.

Four alpine‑fed rivers—the Upper Murray, Mitta Mitta, Kiewa and Ovens—currently provide about a third of the annual water flow within the lower Murray–Darling Basin. The modelling indicates that increasing aridity will drive pronounced downstream declines in flow and reduce the flushing of sediment.

As more sediment settles, river channels are expected to contract. Other systems may change even more markedly: the Murrumbidgee and Macintyre rivers are likely to be punctuated by sections where channels break down, becoming disconnected from the larger rivers they feed—the central Murray and Barwon, respectively.

“Although many of Australia’s native aquatic and dryland flora and fauna have adapted to a highly variable climate, even moderate climate change risks pushing these aquatic ecosystems to a point where their resilience may fail,” Larkin said.

“Seeds and invertebrate eggs can survive many years buried in dry soil waiting for a flood, but if a flood doesn’t come, they can’t survive.” He added that dryland rivers are threatened by declines in water availability from decreased rainfall, increased temperature and evaporation, greater climatic variability, and by human activities such as river regulation, flow diversion and abstraction, and land use change.

“Water is one of Australia’s most contested resources, and it’s the river and wetland ecosystems, rural communities and agricultural industries that will bear the brunt of a drying climate,” Ralph said. “Dryland rivers are fundamentally important for people.

To make sure the communities that depend on them can continue to survive, it’s vital we protect their lifelines.” The projections underscore the vulnerability of Australia’s dryland river systems and the pressure a drying climate could place on ecosystems and communities that rely on them.