Australia & New Zealand: Water deficits forecast to retreat significantly

24 March 2020

THE BIG PICTURE
The 12-month forecast through November indicates deficits in Australia in Top End, Northern Territory; northern Queensland; around Adelaide in the south; Tasmania; and the southern tip of Western Australia.

Deficits will be severe to exceptional in Top End, and in the Gregory Range in Far North Queensland and coastal areas to the east, but moderate in the eastern Cape York Peninsula. Near Adelaide, exceptional deficits are expected with severe anomalies on Kangaroo Island and near the southern border with Victoria. Tasmania will see moderate to exceptional deficits. In Western Australia, deficits will be moderate near Perth but more intense in the Busselton and Blackwood River regions farther south.

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A large pocket of exceptional surplus is forecast crossing the western Gibson Desert in Western Australia connecting to surpluses of lesser intensity along the De Grey and Fortescue Rivers to the north and a few pockets trailing south. Farther north, surpluses are expected in the northern portion of the Great Sandy Desert and into the Fitzroy River region. Along Western Australia’s southern coast, surpluses are forecast inland north of Esperance. In eastern Australia west of Brisbane, the forecast is for surpluses in the northwestern reaches of the Darling Downs. In coastal areas south of Brisbane nearly to Melbourne, a dappled pattern of deficits, surpluses, and transitional conditions is forecast.

Moderate to extreme deficits are forecast in New Zealand from central South Island to the northern tip of North Island. Severe deficits are forecast for New Caledonia.

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

The forecast through May indicates that deficits will nearly disappear, leaving many parts of Australia with relatively normal water conditions. Deficits will persist, though downgrade, in Western Australia’s (WA) southern tip, along Victoria’s central coast, and in Tasmania. Deficits will shrink in New Zealand, persisting in North Island and in the northern region of South Island, and a small pocket of moderate deficit will persist in central New Caledonia.

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Surpluses will persist with intensity in a large block of Western Australia at the western edge of the Gibson Desert and along several rivers leading north. Severe surpluses will emerge in a large block in the Kimberley region. In eastern Australia, surpluses will persist west of Brisbane in the northwest corner of the Darling Downs, Queensland (QLD) and will re-emerge in pockets along the coast from Gold Coast past Sydney.

From June through July, most lingering deficits will disappear or downgrade, leaving some moderate anomalies in central Tasmania and anomalies more intense in a pocket of western North Island. However, exceptional deficits are forecast to emerge along the northern border of WA and Northern Territory (NT) between the upper reaches of the Ord and Rivers. Moderate deficits in Arnhem Land in eastern Top End, NT will intensify, becoming exceptional. Surpluses in WA will persist near the Gibson Desert, but transition to conditions of both deficit and surplus in the Kimberley. In eastern Australia, surpluses will shrink and moderate in the Darling Downs and along the southeastern coast, but moderate surpluses will emerge inland in northeastern New South Wales (NSW) west of Armidale.

The forecast for the final months – September through November – indicates that surpluses will increase significantly in eastern NSW, shrink near the Darling Downs QLD, persist in WA near the Gibson Desert, and begin to re-emerge in the Kimberley. Exceptional deficits will emerge in a small pocket around Broome on Australia’s northwest coast, and deficits will downgrade in Arnhem Land.

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

IMPACTS
After flooding on the heels of devastating wildfires in Australia exacerbated fire impacts in what scientists call “compound extremes,” the country is in the process of assessing its losses while at the same time facing new threats. Downed trees, weakened by fire and then toppled by torrential rainfall, are blocking roads, damaging cars and homes, and canceling schools. One lakeside community south of Sydney lost 89 homes to fire, only to have subsequent flooding destroy many remaining possessions.

The one-two punch of fires and floods left rivers and streams polluted and churning with ash and debris in a soupy mess that brewed up over a dozen sites with documented mass fish-kills, including some located along 40 miles of the upper Murray River. The ashy wash converted normally acidic waters alkaline and oxygen levels plummeted, asphyxiating the fish, while some fish simply “cooked” to death in the fire-warmed cauldron of the waters. Oyster farmers have shut down some operations located in the estuaries of the coastal southeast, fearing contamination by pollution. Oyster shells turned white in the acidic mix.

Drinking water supply in some areas has suffered as well. The Brogo Dam in New South Wales went from a drought-stricken 10 percent to overflowing in less than 24 hours, contaminating the water and forcing officials to cut off supply to 4,000 customers.

The drought impacts from 2019 are still being assessed but after the warmest and driest year on record, Australia’s sheep stock is the lowest in 100 years, the area sown in cotton is the smallest since 1979, and the wine grape crush is expected to drop as much as 15 percent.

In New Zealand, army troops have been deployed to help deliver water to drought-depleted areas of North Island. The Hoteo River near Auckland is at its lowest level in 37 years and the region’s water utility is recommending shorter showers to conserve supply.

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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