Australia & New Zealand: Water surplus forecast in Murray-Darling

Australia & New Zealand: Water surplus forecast in Murray-Darling

28 April 2020

THE BIG PICTURE
The 12-month forecast through December indicates surpluses of varying intensity in the Murray-Darling Basin in southeastern Australia and also at the mouth of the Murray in South Australia. Surpluses will reach exceptional intensity in pockets, including in South Australia between the Murray River and the Victoria border, and the Riverina area of New South Wales, particularly around Griffith.

Tasmania can expect some surpluses in the northeast, including Flinders Island, but pockets of deficit are expected elsewhere in the state and will be exceptional around Lakes Pedder and Gordon in the southwest. In Queensland, surpluses are forecast in the northwest corner of the Darling Downs west of Brisbane.

In Western Australia, a large pocket of exceptional surplus is forecast crossing the western Gibson Desert connecting to surpluses of lesser intensity to the north along the De Grey and Fortescue Rivers, and to the south trailing to the coast. Surpluses are also forecast for a pocket north of Esperance on Western Australia’s southern coast. Moderate surpluses are forecast in the upper basin of the Victoria River in Northern Territory.

Severe to exceptional deficits are forecast for: Western Australia in coastal areas of the Kimberley Region and in the central Great Sandy Desert; Top End, Northern Territory; and, the Gregory Range in Far North Queensland and coastal areas to the east, as well as the tip of the Cape York Peninsula.

Moderate to extreme deficits are forecast in New Zealand from central South Island through North Island. Some severe deficits are forecast for central New Caledonia.

FORECAST BREAKDOWN
The 3-month maps (below) show the evolving conditions in greater detail.

The forecast through June indicates that widespread surpluses of varying intensity will emerge in the Murray-Darling Basin of southeastern Australia. Surpluses will be primarily moderate along the paths of the rivers but will reach extreme to exceptional intensity in the eastern Basin around Dubbo northwest of Sydney and in the southeast corner of South Australia (SA) between the Murray River and the Victoria (VIC) border. Surpluses will increase in northeastern Tasmania including Flinders Island, and deficits will nearly disappear. In Queensland (QLD), surpluses will shrink somewhat in the northwest corner of the Darling Downs.

Surpluses will persist with intensity in a large block of Western Australia (WA) at the western edge of the Gibson Desert and with lesser intensity along several rivers leading north, and will emerge in a path leading south to the coast. Some pockets of moderate surplus will re-emerge in western SA. Deficits will shrink in QLD east of the Simpson Desert but remain exceptional, and will persist in a pocket farther east as well as a pocket on the northeast coast south of Cairns. Exceptional deficits will emerge along the northern border of WA and Northern Territory (NT), and south of the Barkly Tableland in eastern NT. Deficits will shrink in South Island, New Zealand but increase in North Island and will include severe anomalies. Deficits in New Caledonia will shrink and moderate.

From July through September, surpluses will persist in New South Wales and in SA from the Murray River to the VIC border, but will shrink and downgrade in VIC and in the northwestern Darling Downs in QLD. Intense surpluses will persist in WA in the western Gibson Desert with moderate surpluses leading north and south. Exceptional deficits will emerge in northern WA in the Fitzroy and Ord River regions and across the border into NT. Deficits in Top End, NT will intensify, and deficits will emerge in Far North QLD. Much of the remainder of Australia can expect relatively normal conditions, including Tasmania. Water conditions will also normalize in New Zealand and New Caledonia.

The forecast for the final months – October through December – indicates that deficits will retreat and surpluses will persist in a pattern and intensity similar to the forecast through September with surpluses increasing in VIC and emerging around Darwin on the coast of Top End, NT.

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

IMPACTS
After battling drought for years, farmers in New South Wales are seeing signs that recent rainfall may revive lost acreage. Pastures are returning to lush greenery just in time to save some cattle breeding operations from closing altogether. One family of fourth-generation livestock farmers spent the last three years hand-feeding their herd, watching their pastures and bank account dry up. This season, with increased rainfall in the Murray-Darling Basin, farmers are attempting to restock herds.

New Zealand’s North Island has received so little rain in recent months that Auckland could be heading for a one-in-1,000-year drought. Water storage in the city’s nine dams was below half in mid-April - since the beginning of the year there’s been 65 percent less rainfall. Auckland’s 1.6 million residents would be under water restrictions but for COVID-19 hygiene protocols that encourage frequent hand-washing. Farmers in the Cormomandel Peninsula have stopped milking their cows as dry weather claims pastures. The federal government has earmarked NZD $20 million (USD $12.1 million) for drought relief.

Intense rainfall in late April triggered flash flooding and landslides in New Caledonia. Roads were blocked and power disrupted as up to 200mm (7.9 inches) fell on some areas in just six hours, more than the country’s average for the entire month of April.

NOTE ON ADMINISTRATIVE BOUNDARIES
There are numerous regions around the world where country borders are contested. ISciences depicts country boundaries on these maps solely to provide some geographic context. The boundaries are nominal, not legal, descriptions of each entity. The use of these boundaries does not imply any judgement on the legal status of any territory, or any endorsement or acceptance of disputed boundaries on the part of ISciences or our data providers.

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Many analyses reported in ISciences-authored blog posts are based on data generated by the ISciences Water Security Indicator Model (WSIM). Other sources, if used, are referenced in footnotes accompanying individual posts. WSIM is a validated capability that produces monthly reports on current and forecast global freshwater surpluses and deficits with lead times of 1-9 months at 0.25°x0.25° resolution. This capability has been in continuous operation since April 2011 and has proven to provide reliable forecasts of emerging water security concerns in that time-frame. WSIM has the ability to assess the impacts of water anomalies on people, agriculture, and electricity generation. Detailed data, customized visualizations, and reports are available for purchase.

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