Australia & New Zealand: Water deficits to persist in WA, Tasmania, & New Caledonia

24 August 2017

The Big Picture
The 12-month map (below) indicates a forecast of deficits throughout much of Australia, reaching severe to exceptional intensity in: the far west reaches of Western Australia; southwestern Queensland; southern South Australia; coastal Victoria; most of Tasmania; and New Caledonia.

Some surpluses are forecast in eastern Queensland west of Bundaberg, trailing north.

Impacts
Projections for Australia's 2017-18 wheat harvest have been downgraded by the National Bank of Australia to an 8-year low due to severe drought stress, with the possibility of further reductions if rainfall continues below average. Likewise, the Australian Oilseeds Federation estimates that the canola crop will be a million tonnes below last year's.

The unusually dry winter has led researchers to conclude that the bushfire season could begin as early as late August, well before the official start on October 1 and before winter is even over, describing conditions as "dangerously primed for major bushfires." Rainfall averages this winter have been very much below average, according to the Australia Bureau of Meteorology, and conditions through July have improved only slightly. The agency's most recent outlook issued 17 August projects drier than usual conditions September to November in Western Australia.

Heavy precipitation in the form of both rain and snow produced flooding and landslides on South Island, New Zealand in late July and mid-August that necessitated the deployment of at least 200 troops from the New Zealand army. A state of emergency was declared in Christchurch, Timaru, and Otago in July, and flooding left the city of Dunedin - population 120,000 - accessible only by air. Hundreds of homes were evacuated, major highways were cut off, three bridges were damaged, and some flights were cancelled at regional airports. Between July 21 and 22, parts of Dunedin received 225 mm (8.9 inches) of rain, four times the average for the entire month of July.

Forecast Breakdown
The 3-month maps (below) for the same 12-month period show the evolving conditions.

As is apparent in the time series, exceptional deficits observed in recent months over much of Australia should diminish considerably in the near-term and through April 2018.

However, from August through October significant deficits are forecast in: Western Australia from the Hamersley Range in the north through the wheat belt to the southernmost tip of WA; from Adelaide along the southern coast through Victoria and New South Wales and in the eastern Murray-Darling Basin; Tasmania; northern Queensland and around the Gulf of Carpentaria; Top End in Northern Territory; and New Caledonia. Deficits may be exceptional north and south of Perth; east of Melbourne; central Tasmania; around the Gulf of Carpentaria; and Darwin. Deficits in the southwest tip of Western Australia and in Tasmania may linger through April 2018. Conditions in the Kimberly Plateau in the northwest will transition to primarily surplus, but both deficits and surpluses will persist east of the Ord River to the Victoria River. Along Queensland’s northeast coast surpluses will persist near Mackay, with both deficits and surpluses directly south from Rockhampton to Bundaberg.

Past October deficits will continue to retreat, though intense deficits will persist in WA’s southwestern tip and in Tasmania. Moderate deficits will continue to emerge in Victoria and New South Wales. Conditions in New Caledonia and New Zealand are expected to be near-normal.

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

Note on Administrative Boundaries
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