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The drought conditions experienced across much of Australia in 2004-05 are evident by analysing the deviation of 2004-05 rainfall from the long-term (30 year) average annual rainfall, as illustrated in map 3.2. A significant proportion of central Western Australia and central Australia received less than half of their average annual rainfall for 2004-05. Above average rainfall was experienced in relatively few areas.
In most parts of Australia, only a small proportion of rainfall becomes run-off into rivers, lakes, dams and aquifers. This is due to the high rate of evapotranspiration and variability in the amount of rainfall. It is also a result of generally flat topography across most of the continent. Run-off is high in northern Australia and parts of Tasmania where annual rainfall is relatively high. Run-off in 2004-05 was estimated to be 242,799 GL (9% of the estimated rainfall for 2004-05). The highest amounts occurred in the following drainage divisions:
Most of Australia received below average annual run-off for 2004-05 (map 3.3). The northern coastline and most of the eastern half of the continent only received 50-75% of average annual run-off in 2004-05, while a large proportion of Western Australia received below 25% of average annual run-off. The only region of Australia that received above average annual run-off in 2004-05 was the south-western corner of Western Australia (110%).
Groundwater recharge is the inflow of water to the groundwater system from the Earth's surface. Infiltration of rainfall and its movement to the watertable is one form of natural recharge.
The amount of groundwater recharge for 2004-05 shows a similar geographical pattern to that of run-off across the country. Where it differs is due to the influence of soil texture and other biophysical characteristics.
Average annual deep drainage was found to be highest in Tasmania, the south-eastern corner of Australia, the northern tip of Western Australia and the area around Darwin in the Northern Territory. Most of Australia had below average annual deep drainage.
Surface water and groundwater are stored in a number of ways to supply agriculture, industry and urban users. Some of these storages include: large dams, farm dams and aquifers (underground storage).
There are 501 large dams in Australia (map 3.4). A large dam is defined as a dam with a crest height of greater than 15 metres, or greater than 10 metres but meeting other size criteria.
The progressive decline in the water storage level of large dams across much of Australia during the period from July 2001 to June 2005 is shown in maps 3.6 and 3.7. The decrease in storage level (expressed as a percentage of total storage capacity) is apparent in the majority of drainage divisions, particularly those with significant population and industry; for example, the Murray-Darling, South-East Coast, North-East Coast and South-West Coast drainage divisions.
Water use is important to quantify because it gives society a baseline for the amount of water that it needs to operate. Measuring patterns of water use is important when predicting future land use, developing policy initiatives, or when reviewing the impact of present and past practices. For example, they give an indication of where water use efficiency programs or the buy-back of water licences should be focused. An assessment of water use by industry and households enables water managers to target management tools like drought contingency programmes (e.g. water restrictions). Comparing water use with the economic value generated shows which activities are returning more economic value to society, as a result of using the resource.
Water use in the economy
The total amount of water extracted from the environment in 2004-05 was 79,784 GL (24% of Australia's total water resource). Of this 60,436 GL was used in-stream (mostly by hydro-electricity generators) and 1,000 GL of environmental provisions were returned to the environment (mostly by the Water supply industry) and, therefore, not consumed. The remaining 18,342 GL comprises self-extracted and distributed water consumption, which when added to the 425 GL of water reuse resulted in total water consumption in 2004-05 of 18,767 GL. Almost two-thirds of this total was used by producers in the Agriculture industry (65%) and 11% by operators in the Water supply industry (which includes sewerage and drainage services); households share of total water consumption was also 11% (graph 3.8).
Household water use
Water consumption by households in 2004-05 was 2,108 GL. This compares with 2,278 GL in 2000-01. Overall, there was an 8% decrease in household water consumption between 2000-01 and 2004-05.
The majority of water used in 2004-05 was sourced from distributed water provided by water suppliers (89%); the remainder was from a self-extracted source (including groundwater bores and rainwater tanks). Rates of household water consumption in states and territories for each of the years 2000-01 and 2004-05 are shown in graph 3.10. When compared with rates in 2000-01, household water use per person in 2004-05 fell in all states and territories, except in Tasmania.
Agricultural water use
The Agriculture industry in Australia is the major consumer of water, accounting for 65% of total water consumption in 2004-05.
Of the water used for agricultural production in 2004-05, 91% was used for irrigation of crops and pastures. The remainder was used for other agricultural purposes, such as stock drinking water, dairy and piggery cleaning.
Water consumption in the Agriculture industry fell by 23% between 2000-01 and 2004-05; water consumption for rice irrigation fell by 72% and for cotton by 37% (graph 3.11). The large decrease in the use of water in irrigating rice and cotton crops in 2004-05 can be attributed to the reduced sowings as a result of the dry conditions and, consequently, reduced water availability.
Map 3.12 shows irrigated areas used for crops and pastures as a percentage of total crop and pasture land, by drainage division. The majority of intensive crop and pasture irrigation occurs in the Murray-Darling drainage division. The article Irrigation on Australian farms in the Agriculture chapter provides more information on water use.
Water availability compared with water use in Australia in 2004-05 is shown in table 3.13.
Almost half of Australia's self-extracted and in-stream water use occurred in Tasmania - nearly 98% of Tasmania's self-extracted water was used in-stream for hydro-electricity. Victoria was the highest user of distributed water and New South Wales used the majority of reuse water. South Australia consumed the largest proportion of its total resource (32%), while the Northern Territory (1%) and Tasmania (less than 1%) consumed the lowest proportions, due to their relatively high rainfall and low populations.
The majority of the 11,160 GL of water distributed by water suppliers (10,712 GL or 96%) was sourced from inland surface water (table 3.14). Groundwater accounted for 448 GL (4%), of which just over half was in Western Australia (229 GL). Desalinated sea water accounted for the remainder (0.2 GL).
The three highest water using regions in 2004-05 were the Murrumbidgee Water Management Area (WMA) (New South Wales), the Broken, Goulburn and Campaspe WMA and the Murray River WMA (both in Victoria) (map 3.15). In 2004-05 the top 20 WMAs accounted for 70% of total water consumption; the top 30 WMAs consumed 81%.