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FEATURE ARTICLE: MURRAY-DARLING BASIN
The climate of the Murray-Darling Basin is relatively dry compared to other regions of Australia (map 3.18). Annual rainfall in 2005-06 was lower in the Murray-Darling Basin than in the tropical north, eastern seaboard and south-west of the continent, as well as in Tasmania. However, most of the Basin received more rainfall than central Australia.
Based on long-term averages, the Murray-Darling Basin receives 530,618 GL of annual rainfall. Of this, 94% evaporates or transpires, 2% drains into the ground, and the other 4% becomes run-off (table 3.19).
The latest 2004-05 figures show that industries (including agriculture) and households in the Murray-Darling Basin accounted for more than half (52%) of Australia's total water consumption. Agriculture was the largest user of water in 2004-05 in the Murray-Darling Basin, accounting for 83% of water consumption in the Basin; households (2%) and other industries (2%) consumed minor amounts in comparison. The remaining 13% of total water consumed in the Murray-Darling Basin was by the water supply industry, which includes losses in delivery systems (graph 3.20).
In the Murray-Darling Basin, water is also an essential production input for the electricity and gas industry. In 2004-05, approximately 3% of Australia's electricity and one-third (33%) of the nation's hydro-electricity was generated in the Murray-Darling Basin. Hydro-electricity represented the bulk of the Basin's generated electricity. Approximately 15,900 GL of water was used (non-consumptively) in the Murray-Darling Basin to generate 5,209 gigawatt hours (GWh) of hydro-electricity. The volume of water used in the Murray-Darling Basin represented 27% of Australia's hydro-electricity (in-stream) water use.
Agriculture water use data are available up to 2007-08, however, data on the use of water by source are only available for 2005-06 and 2006-07. The main sources of water used by agriculture in the Murray-Darling Basin were surface and ground water (graph 3.21). These two sources combined accounted for 98% of all water consumed for agricultural production in the Basin. Other sources accounted for the remaining 2% of water consumption, including recycled or reused water from off-farm sources and reticulated mains supply.
In 2005-06, total agricultural water consumption in the Murray-Darling Basin was 7,720 GL, however in 2006-07 water consumption dropped by 38% to 4,772 GL. Due to dry conditions in 2006-07 use of surface water dropped to 3,323 GL, a 49% decrease compared to 2005-06 levels. Agricultural use of ground water increased to 1,338 GL (up 25%) and use of other water sources decreased to 111 GL (down 27%).
In 2007-08, irrigated agricultural water consumption in the Murray-Darling Basin was 3,142 GL, a drop of 1,317 GL (30%) compared to 2006-07 (table 3.22). The agriculture commodities that had the most water applied in the Murray-Darling Basin in 2007-08 were: cereals for grain and seed, excluding rice (26%), pastures, cereals and other crops used for grazing (21%) and grapes (14%). The Basin accounted for all irrigated water consumption in Australia for rice (100%), and the vast majority for cotton (91%), cereals to grain or seed, excluding rice (84%) and grapes (84%).
The volume of water used by the agricultural sector for crops and pastures varies from year to year. This is due to a variety of reasons such as: level of rainfall, volume of water available for irrigation (water allocations), technological improvements in irrigation infrastructure, water trading, input costs and commodity prices. Between 2005-06 and 2007-08, water consumption by some commodities was more variable than others. For example, water consumption for cotton in the Murray-Darling Basin decreased considerably from 1,574 to 282 GL and rice also decreased from 1,252 to 27 GL.
Water storage levels in large dams located in the Murray-Darling Basin has progressively declined from July 2000 to June 2006. Basin storage levels were relatively high between July 2000 and December 2001 (greater than 50% for this 18 month period). From January 2002, the combined storage level in large dams in the Murray-Darling Basin did not increase above 50% except for a brief period in late 2005. There is a pattern of increased storage in the winter and spring months of almost every year. However, the amplitude and duration of water storage increase varies, and this affects the volume in storage (graph 3.23).