Australia & New Zealand: Water surplus forecast for Murray River Basin through March

October 26, 2016

The Big Picture
The 12-month composite map (below) indicates water deficits forecast for coastal South Australia west of Spencer Gulf, along South Australia’s Limestone Coast, western Tasmania, and New Caledonia. Surpluses are forecast along the southwest coast of Western Australia, east of Spencer Gulf, the Murray River Basin, and central Queensland.

Impacts
Flooding in the Gawler River catchment north of Adelaide in South Australia - described by State Emergency Services as a one-in-20-year-flood - damaged properties, forced road closures, and inundated agricultural lands at peak harvest. The extreme weather conditions also damaged transmission towers near Melrose, knocking out power to the entire state of South Australia. Officials estimate that around 1,000 hectares of crops were flooded, with losses between AUD$20 to 30 million (~USD$15 to $23 million). Additional losses were sustained due to flooding on the Broughton River.

Central western New South Wales was also affected by flooding, with agricultural losses estimated by the Department of Primary Industries to be AUD$500 million (~USD$382 million) and rising. Residents of the township of Bedgerabong found themselves on what was nearly an island as the Lachlan River overflowed, isolating the township from nearby Forbes and Condobolin, while residents of Codobolin used boats, jet skis, and tractors to access property and ferry supplies. About 100 flood rescues were performed across the state by emergency responders.

Forecast Breakdown
The 3-month composite (below) for the same 12-month period shows the evolving conditions in more detail.

As shown in the October through December map, exceptional (beyond 40 years) surpluses are forecast to persist in central Queensland, along the southwest coast of Western Australia, east of Spencer Gulf, and in central Australia. Moderate (5 to 10 years) to exceptional surpluses are forecast in the Murray-Darling Basin, and primarily moderate surpluses in a scattered arc across the north from King Sound to the Gulf of Carpentaria. Moderate deficits are forecast to persist along South Australia’s Limestone Coast and in southern Tasmania, and to emerge in South Island, New Zealand. Deficits in North Island, New Zealand and New Caledonia are expected to become less severe.

From January through March surpluses will persist in the Murray River Basin and along the southwest coast of Western Australia. Moderate surpluses will emerge in the Northern Territory from Lake Argyle to the western shore of the Gulf of Carpentaria. Both deficits and surpluses are forecast east of Spencer Gulf. Moderate (5 to 10 years) to severe (10 to 20 years) deficits are expected on the Limestone Coast and in western and southern Tasmania.

The final months – April through June – show a forecast of abnormal (3 to 5 years) deficits persisting across much of Australia with moderate deficits from south of Adelaide to Melbourne, Tasmania, and North Island New Zealand.

(It should be noted that forecast skill declines with longer lead times.)