Water resources
Climate change will present major water resource management challenges given Australia is a naturally dry continent and it has a growing demand for water.
Water resources are currently fully or over-utilised in several important regions. More than 90 per cent of national population growth over the next quarter century – an additional 4.5 million residents – will occur in Sydney, Melbourne, South-East Queensland and Perth.
In 2004-2005, agriculture accounted for 65 per cent of water consumed in Australia. The Murray-Darling Basin is Australia’s largest river basin, accounting for about 70 per cent of irrigated crops and pastures. The Murray Darling Basin, with only 6 per cent of Australia’s total runoff, accounted for more than 50 per cent of Australia’s water use in 2004-2005.
Climate change impacts
Australian average temperatures have increased by 0.9ºC since 1910. With our naturally variable rainfall and existing water resource management challenges, climate change will have a significant impact on our water availability.
Climate change projections indicate that we can expect increased temperatures, reduced rainfall across eastern and far south west Australia, increased rainfall variability and evaporation as well as significantly increased frequency and severity of drought. Changes in the frequency of extreme weather events, including flooding are also anticipated.
These factors will combine to put increasing pressure on our water resources, which are already struggling to keep up with demand.
Reduced precipitation and increased evaporation are likely to lead to water security problems in southern and eastern Australia. Australia is already dealing with scarce water resources in both urban and rural environments.
Since the mid-20th century, winter rainfall in south-west Western Australia has declined markedly. The effects of the decline on natural runoff have been severe, as evidenced by a 50 per cent drop in annual inflows to reservoirs supplying the city of Perth. This has been accompanied by a 20 per cent increase in domestic usage in 20 years, and annual population growth of 1.7 per cent. It is believed that at least some of the observed drying was related to climate change.
This problem is no longer confined to Perth. Since 1997 we have seen inflows to the water storages of Australia’s five largest cities cut in half. Melbourne’s dams have received 65 per cent of long-term average inflows, Brisbane 44 per cent, Sydney and Perth 43 per cent, and Adelaide 65 per cent. Whilst these reductions may yet prove to be temporary, climate change modelling nonetheless projects that climate change will impact on urban water resources.
For example, CSIRO analysis of the impact of climate change on streamflows projected an 8 per cent reduction in the average annual volume of water able to be supplied by the Melbourne’s urban water system in 2020, rising to 20 per cent by 2050.
The Murray-Darling Basin is facing an historically unprecedented situation – with recent years being some of the lowest inflows in 117 years.
The historic overallocations, the current unprecedented drought, and the emerging impacts of climate change mean there is not enough water in the system. The South Australian Government is purchasing water for Adelaide residents and farmers have pulled out fruit trees and production from irrigation districts has been affected.
Wetlands in the MDB have also been affected. For example, severe drought conditions continue to affect the Coorong Lakes and other nationally significant wetlands, floodplains and riverine habitats. Flood-dependent river red gums and black box continue to decline, and understorey vegetation and waterbird and freshwater fish populations are stressed.
Reduced runoff and streamflows
Changes in rainfall combined with increased potential evaporation are expected to result in reduced runoff across most of Australia. In some cases reductions could be severe. In some cases reductions could be severe. Flows are projected to drop 31 per cent in the Stirling Dam catchment in Perth’s hinterland by 2050. A risk assessment for the city of Melbourne indicated average stream flow declines of up to 11 per cent by 2020, and up to 35 per cent by 2050.
Increased drought
Climate models suggest that drought could be as much as 20 per cent more common by 2030 over much of Australia and up to 80 per cent more common in south-western Australia by 2070.
The economic impact of these climatic conditions is significant - the cost to the Australian economy from the 2002-2003 drought was estimated to be $6.6 billion.
Reduced water quality
Climate change is likely to increase the stress on rivers already under pressure from salinity, over-allocation and declining water quality. Higher water temperatures and reduced stream flows will adversely affect water quality affecting human uses and environmental conditions.
Drought conditions are likely to exacerbate erosion and downstream sedimentation. Higher sediment loads enter rivers following extreme rainfall events or extreme bushfire events, both of which are projected to increase with climate change.
Changed climatic conditions are also likely to produce conditions that favour riparian and aquatic weeds and algal blooms.
Changed flood frequency
Increases in extreme rainfall events are projected for many regions, although the impacts are spatially variable. Increased extreme rainfall events are likely to result in more flash flooding, strains on sewerage and drainage systems, and challenges for emergency services.
Impact on the Murray-Darling Basin
Surface water availability across the entire MDB is expected to decline due to climate change. Recent CSIRO analysis indicates large reductions in reliability of water supply in the Murray catchment and southern basin regions are likely by 2030. Anticipated reduction in water availability by 2030 varies between regions, from a 3 per cent reduction in the Paroo to a 21 per cent reduction in the Wimmera.
In volumetric terms, the majority of the impact of climate change is likely to be borne by the environment rather than by water users. At the same time, groundwater extraction is projected to increase.
Irrigated agriculture is particularly sensitive to climate change as relatively modest changes in precipitation and temperature can have substantial effects on the availability of water for irrigation. Effects of this kind are being felt in the Murray Darling Basin due to the prolonged drought.
This information has been sourced from a range of materials, including: ABS 2008 Water and the Murray-Darling Basin - A Statistical Profile, 2000-01 to 2005-06; Coorong inquiry; MDB impacts; CSIRO, 2008, “Water Availability in the Murray-Darling Basin” as part of the Sustainable Yields project; CSIRO/BOM 2007; Hennessey et al, 2007. Ch 11 – Australia and New Zealand, IPCC Working Group II report, Impacts, Adaptation and Vulnerability; CSIRO 2008. Urban water – Water for a Healthy Country Flagship. Howe et al, 2005. Implications of Potential Climate Change for Melbourne’s Water Resources. CSIRO report to Melbourne Water.; Stoekel and Abrahams, 2007 in Managing Water for Australia (eds Hussey and Dovers).; Australia’s Water Resources 2005 (www.water.gov.au); Quiggin et al, 2008 Implication for irrigation in the Murray Darling Basin. Report to Garnaut Secretariat.