A Fraying Lifeline in a Drying Climate

26 May 2020

Research from Macquarie University has revealed a gloomy future for Australia’s river network with dramatic impacts predicted for people, industries and wildlife owing to climate change.

In an article published in Scientific Reports, Macquarie University’s Wetlands in Drylands researchers Zacchary Larkin, Tim Ralph and colleagues modelled how increasing aridity, under even a relatively moderate climate change scenario, will affect Australian inland rivers within 50 years.

Currently, 78 per cent of the Australian continent is classified as dryland. We already know that future climate change is likely to have severe effects on the rivers that – for now – flow through these drylands, reducing flow and water availability.

Their modelling indicates that there will be a concerning degree of desertification, with the arid zone that encompasses the areas of true desert expanding into a large area of the Murray-Darling Basin and almost entirely engulfing the Lake Eyre Basin.

Macquarie River, in dry and wet years. Image by Tim Ralph

Macquarie River, in dry and wet years. Image by Tim Ralph

The humid and dry sub-humid fringes around the Great Dividing Range and coastal areas are also likely to contract. Many inland Australian rivers begin on the western slopes of the Great Dividing Range, and the projected drying pattern could have profound effects on rainfall and runoff in their headwaters.

Of the 29 rivers analysed in this study, 23 are projected to change into another river type. Some, such as the Lachlan and Macquarie rivers, will come to resemble present-day central Australian rivers – only persisting as disconnected channels and waterholes for long periods of time.

The Great Cumbung Swamp and Macquarie Marshes, both internationally important wetlands, much less frequently inundated are also predicted to be impacted with major impacts on the vegetation and wildlife they host.

Four rivers – the Upper Murray, Mitta Mitta, Kiewa, and Ovens – presently provide about a third of the annual water flow within the lower Murray-Darling Basin. But the modelling indicates that aridity will lead to pronounced downstream declines in flow, with less sediment being flushed downstream. As the sediment settles and deposits in these rivers, their channels will become smaller.

Other rivers are expected to change even more dramatically in structure and behaviour. Instead of their current continuous winding course, the Murrumbidgee and Macintyre rivers are likely to be interspersed with sections where the channels break down, becoming disconnected from the larger rivers they flow into, the central Murray and Barwon rivers, respectively.

Lead author Zacchary Larkin says “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. 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.”

“Dryland rivers exist in marginal environments and are threatened by declines in water availability from a range of sources – the impacts of climate change, such as decreased rainfall, increased temperature and evaporation, and greater climatic variability, as well as other human activities, like river regulation, flow diversion and abstraction, and land use change”, Larkin concluded.

Study author Tim Ralph says “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. 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.”

Filed under: Research Science & nature