Climate change and water resources in the Murray Darling Basin ...

ABARE CONFERENCE PAPER 02.11
Murrumbidgee — that collectively stretch for almost 7000 kilometres. Much of the basin
is extensive plains and low undulating areas, mostly below 200 metres above sea level.
An important consequence of the extent of the Murray Darling Basin is the great range of
climatic conditions and natural environments including rainforests in the cool and humid
eastern uplands, the temperate mallee country of the south east, the subtropical areas of
the north east as well as the semiarid and arid lands of the far western plains.
While the Murray Darling river system is large in terms of its catchment area and length,
it is small in terms of surface water runoff. Almost 90 per cent of the basin contributes
virtually no runoff to the river systems, except at times of flooding. The catchments draining
the Great Dividing Range — the Murrumbidgee, Murray and Goulburn–Broken —
contribute almost half of the mean annual runoff while occupying only 11 per cent of the
area of the basin. The variability of rainfall in the basin means that the river systems are
subject to considerable variability of flows. Because of this large variation in stream flows,
storage dams are needed to provide continuity of water supplies for urban, industrial and
agricultural uses. At the same time, the Murray Darling Basin provides unique aquatic,
terrestrial and wetland habitats for native plants and animals.
The Murray Darling Basin accounts for more than 40 per cent of agricultural production in
Australia. Valued at an estimated A$34 billion, broadacre properties grazed around 5.9
million beef cattle and 51 million sheep in 1999-2000. Wheat production exceeded 12
million tonnes in the same year. While the Murray Darling Basin is dominated by extensive
dryland agriculture, irrigated agriculture in the basin accounts for around 70 per cent of
all water used in Australia (Crabb 1997). An estimated 1.3 million hectares was irrigated
in 1996-97 with irrigated pasture accounting for more than 50 per cent of the total area
irrigated (figure 1). River systems within the Murray Darling Basin provide domestic water
supplies to more than 10 per cent of the Australian population and support a range of
industries.
Figure 1: Area irrigated in the Murray Darling Basin, by crop type
700
600
500
400
300
200
100
’000 ha
Irrigated cotton
Source: ABS Agricultural Census 1996-97
Irrigated pasture
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Other irrigated crops