Australia & New Zealand: Water deficits to persist in southwest WA and Tasmania

19 July 2017

The Big Picture
The 12-month composite map (below) indicates a forecast of severe to exceptional deficits in the far west reaches of Western Australia, including Perth; most of Tasmania; the center of the country south of the MacDonnell Ranges; and New Caledonia. Moderate deficits are forecast for much of Australia’s eastern half.

Surpluses are forecast for central Arnhem Land in Northern Territory; from the Kimberly Plateau to the Victoria River in the northwest; and west of Bundaberg in eastern Queensland, trailing north.

June rainfall was below average for much of Australia, according to the Australian Bureau of Meteorology, and conditions in southwest Western Australia were the lowest on record. Kalannie, northwest of Perth, received less than one tenth the rainfall this growing season compared to 2016 - 12mm of rain (.47 inches) compared to 150mm (5.9 inches). The situation is potentially devastating to wheat and canola farmers, some of whom are faced with the loss of their family farms. The West Australian Minister for Agriculture and Food is urging the Federal Government to consider drought assistance. Experts are predicting that the nation's 2017 wheat production will be 10 million tonnes below last year. 

Dry conditions also have Tasmanian dairy and sheep farmers nervous after the driest June in 10 years - less than half the June average - and Hobart experienced its driest start to winter in 120 years. As of July 17, the state's 43 water storages were at 50.7 percent

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

As the time series indicates, conditions through central Australia should moderate in the coming months. A vast pocket of exceptional deficit stretching from Northern Territory into Queensland observed in prior months is expected to dissipate. However, severe to exceptional deficit conditions will continue through September in southwest Western Australia, Darwin in the north, Tasmania, coastal Victoria into New South Wales, and New Caledonia. Deficits from Perth south, over Tasmania, and in New Caledonia may linger into early 2018.

Observed surpluses reaching from the Kimberly Plateau to the Victoria River in the northwest, and west of Bundaberg in eastern Queensland will transition to both deficit and surplus through September but may transition back to surplus from October through December.

The final months of the forecast period – January through March 2018 – indicate persistent deficits near Perth and over Tasmania, as mentioned, along with the emergence of deficits at the intersection of Northern Territory, Queensland, New South Wales, and South Australia.

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

Note on Administrative Boundaries
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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 0.5°x0.5° 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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