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In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
Salinity - Risk and Hazard
Australia
Where is there dryland salinity risk in the year 2000?
Risk and Hazard - definitions
'Risk? and ?hazard? are often used as equivalent terms in common language. Generally ?risk? is predictable, and numerically quantifiable, whereas hazard is a qualitative evaluation or estimate.
The definitions of ?hazard? and ?risk? adopted by the Audit are:
?hazard? - anything that can cause harm to an asset (e.g. salt loads in lands where groundwaters have potential to rise);
?risk? - estimation of the expected amount of harm that will occur to the asset when a condition occurs (e.g. shallow saline groundwaters under cropland).
For ease of reading, the term ?risk? has been used in narrative text. Readers should note that ?risk? totals quoted for Australia include both areas of risk and hazard.
Assessment approach
Regional-scale, dryland salinity risk or hazard assessments were undertaken by State/Territory agencies using:
- information on groundwater levels and trends;
- known incidence of salinity;
- soil characteristics; and
- topography.
For those States with data on groundwater levels and trends, land units with groundwater within 2 m of surface, or within 2 to 5 m and with well demonstrated rising watertables (except for New South Wales) were classed as being at high risk of dryland salinity. A groundwater level of 2 m was selected in line with documentary evidence that where levels are in the 1 m to 2 m levels, salinisation of the soil occurs adversely affecting crops and native vegetation (Nulsen 1981, Talsma 1963).
The assessments used existing data held by States and were constrained by available data and financial resources, and timeframes. The assessments exposed a number of limitations in the groundwater data quality and coverage across States. Difficulties encountered in applying the same landscape analysis approach across States meant that a range of methods and scales were adopted.
Even where there were perceived to be good quality groundwater data (e.g. in Victoria, south-west Western Australia), the forecasted groundwater levels to 2020 and 2050 are based on straight-line projection of recent trends in groundwater levels. Due to inadequacies in current methods, accurate groundwater surfaces cannot be developed with the existing distributed data. This was also an outcome of the Audit?s Salt Scenarios 2020 project focused on the Great Southern region of Western Australia.
Where sufficient groundwater level and trend data were available as in Western Australia, South Australia, Victoria and New South Wales, the assessments have been accepted as risk assessments, as the drivers of dryland salinity have been identified as operating for some time and there is confidence in the understanding of the current and future impacts of shallow water tables.
Where data on groundwater levels and trends are sparse such as in Queensland and Tasmania, assessments were based more on knowledge of land attributes and dryland salinity incidence. Groundwater data were used where available to provide extra confidence in the assessments. In these States the assessments were considered to be hazard assessments as there is less knowledge about the current and likely impacts of shallow watertables on dryland salinity. The existing hazard assessment of the Northern Territory was based mainly on vegetation type, aquifer attributes, landscape and depth of weathering attributes, rather than any trends in groundwater.
Groundwater trend analysis at the scales used will only provide an overview. It is important to recognise that the risk analyses and conclusions presented in this report provide State-wide appreciations of the area at risk and impacts of dryland salinity. Trends at the local level (farm and paddock) can be ascertained from individual bores whose location with respect to landscape position and hydrogeology is well known.
The Audit?s assessment using groundwater data has identified areas where dryland salinity impacts from shallow groundwaters are known or expected to occur. The hazard assessments have identified those areas where dryland salinity could potentially exist given changes in land use that affect the water balance. This information should not be interpreted as actual areas affected since the assessments are likely to overestimate areal extent particularly in dissected (hilly) landscapes. Rather they identify areas or regions within which dryland salinity occurs or could occur.
| State / Territory | Hazard | Risk |
|---|---|---|
| New South Wales | X | |
| Victoria | X | |
| Queensland | X | |
| Western Australia | X | |
| South Australia | X | |
| Tasmania | X | |
| Northern Territory | X | |
| Australian Capital Territory* | n/a | |
Within the ACT the dryland salinity problem is considered to be very minor. Readers should refer to the New South Wales assessment for a broader context of dryland salinity within and adjacent to the ACT.
Click here to download and view map in.pdf format (1.2MB)
Where is there risk of dryland salinity occurring in our landscapes in 50 years time?
Click here to download and view map in.pdf format (1.6MB)
This map represents a compilation of dryland salinity risk and hazard mapping for the year 2050. The map shows the broad distribution of areas considered as having either a high salinity risk or a high salinity hazard. In southern Australia where groundwater level and trend data are available, more confident assessments have been possible. However, in northern Australia groundwater data for trend analysis are very sparse or non-existent. In these regions, salinity assessments have been based on the presence of geological, landscape, regolith, land use and climate attributes which are the prime drivers of salinity. This national map provides a basis for identifying those regions where more detailed assessments are warranted, and where land use changes should be targeted if the risks are to be managed.
The bulk of non-agricultural areas in Western Australia, South Australia and western New South Wales were considered to have a very low salinity risk and were not assessed.
Approximately 5.7 million hectares of Australia?s agricultural and pastoral zone have a high potential for developing dryland salinity through shallow watertables. Predictions based on groundwater trends, field surveys and landscape characteristics indicate that unless effective solutions are implemented, the area could increase to 17 million hectares by 2050. Most is agricultural land (more than 11 million hectares).
Dryland salinity coincides with those agricultural zones in which natural vegetation has been replaced-often many years ago-with land use systems that do not use water to the same extent as the natural vegetation.
The largest areas of dryland salinity are in the agricultural zone of south-west Western Australia. Groundwater levels in this zone are still rising and over 4 million hectares have areas at risk; an area that could double by 2050. Large areas are also at risk of dryland salinity in South Australia, Victoria and New South Wales, mainly in the Murray-Darling Basin where groundwater levels are still rising.
An existing salinity hazard assessment for the Northern Territory (Tickell 1994b) concluded that the overall hazard for the Territory is relatively low. No further assessment was carried out as part of this Audit. Also the bulk of the non-agricultural area of Western Australia, and far western New South Wales were considered to have a very low salinity risk, and were not included.
Although northern Australia has far less dryland salinity than temperate Australia, dryland salinity could become a problem for many catchments with high salt stores if water balance changes led to groundwater rises. In Queensland an estimated 3.1 million hectares is considered to have a high hazard, and more rigorous assessments of the risks under land use are a priority. The extent of salinity in northern Australia can be minimised by preventive management, maintaining water balance by protecting and ensuring vigour in native vegetation.
How may dryland salinity risk change over time?
In the face of a three-fold increase in salinity over the coming decades:
- We need to recognise that there is no quick fix. Salinity can be managed by prevention (greatest potential being in northern Australia), treating the cause, ameliorating the symptoms, living with it or a combination of these.
- Salinity management requires knowledge about soil, salt, water and vegetation; integrated with knowledge about groundwater flow systems.
- We need to implement a landscape function approach to the management of on-site and off-site impacts of dryland salinity. In some areas this may require a mix of biological, engineering and industrial responses in accordance with biophysical and hydrogeological systems.
- We need to enhance monitoring systems to allow evaluation of the effectiveness of management responses and to build on our understanding of landscape processes.
Figure: Animated map of areas of high risk or hazard of dryland salinity in Australia 2000 to 2050
To view animation, ensure that your browser options are set to "play animations"
Areas (ha) with a high potential to develop dryland salinity in Australia.
| State/Territory* | 1998/2000 | 2050 |
|---|---|---|
| New South Wales | 181 000 | 1 300 000 |
| Victoria | 670 000 | 3 110 000 |
| Queensland | not assessed | 3 100 000 |
| South Australia | 390 000 | 600 000 |
| Western Australia | 4 363 000 | 8 800 000 |
| Tasmania | 54 000 | 90 000 |
| Total | 5 658 000 | 17 000 000 |
* The Northern Territory and the Australian Capital Territory were not included as the dryland salinity problem was considered to be very minor.
Where might we have opportunities for prevention?
Prevention and protection: opportunities in northern Australia
Treating the cause of salinity through recharge reduction may be effective in reversing salinisation in only a few responsive groundwater systems. Once the salinisation process is under way it is extremely difficult to slow, halt or reverse in order to protect water and land resources. Prevention is a far better investment than any attempt at control or management.
Northern Australia presents opportunities to avoid the dryland salinity problems of temperate Australia. Broad-scale clearing without recognition of salt stores and the resulting change in water balance is a recipe for problems, whether it is in 20 or 100 years. Wise management now to protect the landscape and prevent dryland salinity will prove far more cost-effective than any attempts to solve the problem once it occurs.
While salinity analysis has focused on southern Australia, sound scientific evidence (Bui et al. 1996, Williams et al. 1997, Bui 2000, Gordon et al. 2000, Gunn 1967, Shaw et al. 1994) shows that all the factors that contribute to salinity hazard also exist over large areas of the semi-arid zones of northern Australia. Two factors that must be present for a salinity hazard to exist after clearing or change in vegetation cover are :
- presence of stored salt in the soil, regolith or groundwater systems, and
- an increase in the water draining beneath the root zone following tree clearing or vegetation change.
Hazard assessments have been carried out in Queensland as part of the Audit program and previously for the Northern Territory (Tickell 1994a, 1994b).
An assessment is yet to take place for northern regions of Western Australia.
Northern Australia has seasonal patterns of high evaporation and summer rainfall. A common misconception is that these patterns mean that land clearing and other vegetation management cannot increase the amount of water draining below the root zone to intercept the salt and move it to lower positions in the landscape and to rivers, streams and wetlands.
Hydrogeological evidence does not support this perception. The summer wet season rainfall pattern in northern Australia is concentrated between December and April. These rainfall patterns respond to vegetation change (particularly the removal of deep-rooted perennial species) in a similar way and extent to the winter-dominant rainfall patterns of southern Australia where salinity is widespread (Williams et al. 1997, Gordon et al. 2000, Stirzaker et al. 2000). A change in vegetation can significantly increase the water that drains (deep drainage) beneath the root zone in northern and central Queensland. It is important to conduct water balance analysis over periods of a day or so, to see evidence of increased deep drainage following clearing. Coarse, monthly analysis of water balance can be misleading and is the basis for current misconceptions.
Key messages
- Hazard assessment has confirmed that large areas of the tropics and subtropics have a potential salinity problem if clearing occurs.
- Broad-scale land clearing with little or no regard for the salinity hazard is a recipe to repeat the problems of temperate Australia.
- Assessment of areas identified as having a hazard, particularly areas of extensive clearing in central and southern Queensland, is essential and would underpin the development and implementation of vegetation management policies and guidelines.
- Opportunity exists for a major national, well-focused investment in preventive action in northern Australia.
Further information
- Australian Dryland Salinity Assessment 2000 report
- National Technical Overview Report of the State-based dryland salinity assessments
- Dryland Salinity Evaluation and Monitoring Report
- Australian Groundwater Flow Systems Technical Report
- National Dryland Salinity Program
- National Action Plan for Salinity and Water Quality
Australian Dryland Salinity Report
Link to Map maker to make a map using this information.
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