Water availability – 2004-05

Australian water resources are highly variable, both geographically and temporally. Managing competing water demands against the variable supply becomes more difficult, and the need for precision in management arises, as more of the resource is relied on for extraction and use. Water availability is dependent on the distribution of rainfall, the volume of runoff and recharge, and the ability to harvest, store and distribute water.

Rainfall

  • In 2004–05, the total volume of rainfall for Australia was 2,789,400 gigalitres. This is equivalent to an Australia wide average rainfall of 364 mm, which was substantially below the long-term average rainfall of 457 mm. Only in south-west Western Australia and northern New South Wales was rainfall at or above the long-term average.
  • The 2004–05 year 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.
  • On average, 90 per cent of rainfall is directly evaporated back to the atmosphere or used by plants; only 10 per cent 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.

Graph showing Rainfall in 2004-05 was substantially below average resulting in many water storages going dry.

Average annual rainfall for Australia from 1900 to 2005
Sourced from Bureau of Meteorology

Runoff and recharge

  • 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 per cent of total inflows, and groundwater recharge 17 per cent.
  • The total water resource in 2004–05 was approximately 20 per cent less than the total in 1996–97 (the year of the National Land and Water Resources Audit’s last national water resource assessment). This is primarily because of a series of dry years since 1997, although double counting of surface water and groundwater resources was also acknowledged as an issue in the previous National Land and Water Resources Audit.

Distribution of water resources

  • In 2004-05, more than 60 per cent of Australia’s total runoff was in Australia’s three northern drainage divisions. Runoff was greatest in the Gulf of Carpentaria drainage division (62,060 gigalitres), the Timor Sea drainage division (50,240 gigalitres), and the North-East Coast drainage division (40,210 gigalitres).
  • In contrast to the high levels of runoff in northern Australia, the Murray-Darling Basin was relatively dry, accounting for only six per cent of Australia’s runoff in 2004–05.

Dam storage levels

  • Australia’s total large dam storage capacity in 2004–05 was 83,853 gigalitres. A total of 44,164 gigalitres was held in water storages on 1 July 2004, and this was reduced by 10 per cent to 39,959 gigalitres during the year to 30 June 2005.
  • The greatest declines in large dam storage levels from 2002 to 2005, in percentage terms, were in New South Wales (33 per cent) and Victoria (22 per cent). There was an overall decline of 18 per cent across Australia during this three-year period.
  • In June 2005, large dam storages were at their fullest in Western Australia (at 83 per cent) and the Northern Territory (at 70 per cent). The states with lowest levels were New South Wales (at 33 per cent) and Victoria (at 39 per cent).
Rainfall in 2004-05 was substantially below average resulting in many water storages going dry.
Rainfall in 2004-05 was substantially below average with water storages being reduced significantly.
Image by Ryan Morris, sourced from SKM
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Last Updated 11/05/2007