Water availability
Australia's water resources are highly variable, and range from heavily regulated working rivers and groundwater resources, through to rivers and aquifers in almost pristine condition.
Rainfall in Australia is highly variable from year to year, and season to season. On average, only a tenth of this rainfall becomes runoff into rivers or recharge into groundwater aquifers. We rely on groundwater to meet our water needs where surface water is unavailable. Groundwater makes up nearly one-fifth of Australia's 'sustainable' water resources.
Australians live on the driest inhabited continent in the world. Rainfall is variable and droughts are common, and water resources in many areas are scarce. Where surface water is unavailable, we rely on groundwater to meet our water needs.
Rainfall
Rainfall in Australia is highly variable from year to year, and season to season. Average rainfall across Australia ranges from less than 200 mm per year in central Australia, to more than 2000 mm per year in some coastal areas in the far north and far south.
The most recent water figures from the Australian Bureau of Statistics report that in 2004-05, the total volume of rainfall for Australia was 2,789,400 gigalitres (1 gigalitre is approximately the same amount of water as in 500 olympic swimming pools). This is equivalent to an Australia-wide average rainfall of 364 mm, which is substantially below the long-term average rainfall of 457 mm. Only in southwest Western Australia and northern New South Wales was rainfall at or above the long-term average.
The 2004-05 period was preceded by more than five years of below-average rainfall across large parts of Australia, particularly the eastern states and south-west Western Australia. While both 2006 and 2007 saw an Australia-wide average rainfall slightly above the long-term average, conditions have remained relatively dry in the south-east and south-west of the country.
Runoff
On average, 90% of rainfall is directly evaporated back to the atmosphere or used by plants; only 10% becomes runoff into rivers or recharge into groundwater aquifers. This runoff and recharge is highly variable, resulting in significant differences in water availability across Australia.
In 2004-05, total runoff was estimated at 242,800 gigalitres and total groundwater recharge at 49,200 gigalitres. This gives a total inflow to Australia's surface and groundwater resources of 292,000 gigalitres (10% of rainfall). Based on these figures, runoff to rivers made up 83% of total inflows, and groundwater recharge accounted for 17%.
Runoff is not evenly distributed across the country. In 2004-05, more than 60% of Australia's total runoff was in Australia's three northern drainage divisions:
- Gulf of Carpentaria drainage division (62,060 gigalitres)
- Timor Sea drainage division (50,240 gigalitres)
- North-East Coast drainage division (40,210 gigalitres).
In contrast the Murray-Darling Basin was relatively dry, accounting for only 6% of Australia's runoff in 2004-05.
Stored water
There are 501 large dams in Australia. In 2004-05 the total storage capacity of these dams was 83,853 gigalitres.
- Information on current dam levels across Australia is available from the Water Resources Observation Network.
In addition to large dams, there are more than two million farm dams across Australia. These dams are estimated to have a total storage capacity of 8000 gigalitres.
Groundwater
Groundwater makes up approximately 17% of Australia's 'sustainable' water resources. Much of Australia's groundwater is drawn from the Great Artesian Basin - the largest groundwater reserve of its type in the world. It covers 22% of the Australian continent and contains water that is up to two million years old.
Determining how much groundwater is available is difficult. Compared to surface water systems, we know little about groundwater systems, and in many areas across Australia, surface water and groundwater resources are physically connected (for example a lake might recharge a groundwater system, or groundwater might keep a river flowing when it is not raining).