Water resources in a changing climate: Western Victoria

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Water availability is a key issue in Australia. A changing climate will place greater demand on water resources. We need to factor the risks associated with climate change into the ways we use water.

Key facts

• Around 89% of Australia’s total rainfall evaporates or is transpired by plants into the atmosphere. Only around 9% runs off into streams, rivers and storages. The remaining 2% drains below the root zone into groundwater aquifers and, from there,into rivers.
• Exactly how much rainfall returns to the atmosphere and how much is available to recharge soil, surface, and groundwater stores depends mainly on the amount of energy from sunshine, and to a much lesser degree on the type of soil and vegetation, and the management practices on the land.
• Annual crops and pastures use less water per year than perennial vegetation,including trees, primarily because of their short growing seasons and shallower root systems. The larger canopies of native and plantation forests add to their higher evapotranspiration.
• Around 65% of continental Australia’s total runoff occurs in far northern Australia and coastal Queensland. Only about 7% of runoff occurs in the Murray-Darling Basin where more than 50% of Australia’s water is used.
• Around 65% of water extracted from the environment in Australia is used for irrigated agriculture (almost 90% of this in the Murray-Darling Basin), 14% for industrial uses, 11% for urban household consumption and 3% for other rural uses,such as stock and domestic needs.
• Pastures use about 35% of irrigation water in Australia, followed by horticulture(16%), cotton (15%), cereals (13%), sugar (12%) and rice (6%).
• Climate variability has by far the greatest impact on seasonal water availability and water balances in Australia—significantly greater than impacts from human extraction or land management practices. Certain river basins are exceptions.
• Shifts in climate that result in less rainfall and higher temperatures are the greatest threat to our water resources.