The commitment of all states and territories to the National Water Initiative (NWI) placed clear and limiting criteria on the abstraction of additional fresh water from the environment. Under these criteria, it is recognised that water resources across southern Australia are already either fully committed or overcommitted. On the basis of current planning, Australia’s major metropolitan areas will meet future urban demand through a combination of water conservation and new sources, based on either sea water or recycled water. The Sustainable development panel report73 concluded that a larger future population (and an increasing ‘footprint’ of cities extending out into the surrounding regions) means increased water prices and less water for the environment. Based on a review of current metropolitan water planning, the former is highly likely but the latter will not necessarily occur. However, meeting increased demand without taking more fresh water from the environment almost certainly will mean increased energy inputs to our water supply (e.g. for water recycling).
Groundwater currently represents 16% of total water use in the Murray–Darling Basin. Under current water-sharing arrangements, groundwater use could increase by 2030 to be more than a quarter of total water use. A quarter of current groundwater use will eventually be sourced directly from induced streamflow leakage, which is equivalent to about 4% of current surface water diversions. Current groundwater use is unsustainable in 7 of the 20 high-use groundwater areas in the Murray–Darling Basin and will lead to major falls in groundwater levels in the absence of management intervention.5
Across northern Australia, rainfall and run-off are highly variable and decrease away from the northern coast. This pattern of run-off, combined with the generally low relief of much of the coastal area, provides little opportunity for significant increases in surface water storages. Potential new dam sites are mainly in the upper reaches of catchments, where rainfall is lower and more sporadic, and potential evapotranspiration is higher. Large storages are needed to compensate for evaporative losses, and storage volumes need to be much larger than in southern Australia, all things being equal. There are few large-scale opportunities to increase surface water storage that satisfy all these requirements. On the basis of changes to flow regimes only, existing plans by jurisdictions to increase water use will have little impact on water resources at the region scale in the next two decades.
Under the future projected climate of Tasmania, of the 24 proposed irrigation schemes considered, 10 can be supplied with their full demand for water in all years. Another 5 can be supplied with their full demand for water in more than 80% of years, 4 can be supplied with their full demand in 50–80% of years, and the remaining 5 can be supplied with their full demand in less than 50% of years. Future development of groundwater to extractions of 25% of recharge in the Mella, Togari, Wesley Vale and Scottsdale groundwater assessment areas is expected to have only localised impacts on groundwater levels and streams in irrigated parts of these areas. Between 2% and 4% of the area’s subcatchments and between 12 and 15 of the 150 key ecological sites are potentially impacted under the likely future climate and levels of development.16
In the south-west of Western Australia, significant gaps between water yields and demands are expected by about 2020 in the areas where surface water resources are used for irrigation. Significant gaps between groundwater yields and demands are expected by about 2020 for areas around Perth. The Water Corporation’s Water Forever strategic plan74 is designed to meet the challenge to provide water in an even warmer and drier climate, for twice as many people, and with less environmental impact. For the purposes of this plan, a climate scenario that projects a 20% decline in rainfall by 2030 from the 1990 baseline was adopted. A rainfall reduction of this magnitude is estimated to reduce yields from existing dams and groundwater sources to about 165 gigalitres per year, from average yields of 260 gigalitres per year since 2001. Further, the scenario considers a 40% decline in average annual rainfall by 2060 from the 1990 baseline, to less than 500 millimetres per year. This would further reduce yields from existing dams and groundwater sources, to an estimated 55 gigalitres per year. At these levels, dams would cease to be a reliable part of Perth’s water supply (in 2010, there was almost no usable run-off into Perth’s dams). Water Forever provides a portfolio of options to manage Perth’s demand and supply balance to 2060 by reducing water use by 25%, increasing wastewater recycling to 60% and developing new sources.
Many of Australia’s recent water resource decisions reflect the commitment to the principles of the NWI. An optimistic assessment of future risks from water resource development relies on continuing adherence to these principles through times of high development pressure and pressing needs to recover water for the environment.