Dryland salinity extent and impact

More than 1 million hectares of agricultural land in the south-west of Western Australia is severely affected by dryland salinity. Dryland salinity is a major cause of land degradation and remains a threat to 2.8–4.5 million hectares of highly productive, low-lying or valley soils.

The opportunity cost of lost agricultural production from dryland salinity in the south-west of WA has been calculated to be at least $519 million per year since 2009/10. Dryland salinity does not affect all farmers equally.

For a snapshot on salinity and diagnosis refer to the MyCrop salinity fact sheet.

Estimating the extent of dryland salinity

Landholders and scientists have several ways of estimating the extent and location of dryland salinity, including estimating or measuring the actual area of salt scald (no plant growth), measuring areas of severely reduced plant growth, and calculating the area with shallow saline watertables (from bore data).

Monitoring groundwater levels provides the information needed to estimate dryland salinity expansion and when that may occur.

Estimates of current and projected extent of salinity in WA have been published by the Australian Bureau of Statistics, Department of Agriculture, National Land and Water Resources Audit, the Land Monitor project and Salinity Investment Framework.

Impact

The opportunity cost of lost agricultural production from dryland salinity in the south-west of WA was calculated to be at least $344 million per year in the period 2003/04 to 2008/09 and $519 million per year in the period 2009/10 to 2013/14. However, dryland salinity does not affect all farms equally: farms in flat valley floors are most affected.

The last scientific evaluation of the extent of salinity in WA identified that between 0.9 and 1.1 million hectares was severely affected. Private land accounted for between 0.74 and 0.84 million hectares. The impact of dryland salinity on agricultural crops is variable.

Dryland salinity remains a potential threat to 2.8–4.5 million hectares of productive agricultural land. The long-term extent of salinity may take from decades to centuries to develop, especially in areas where recharge is episodic, clearing was staggered, the area cleared is small, or where watertables are deep.

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Dryland salinity estimates

Australian Bureau of Statistics (1955–2002)

Since 1955, the Australian Bureau of Statistics (ABS) agricultural census has asked landholders to estimate the 'area of salt-affected land which was previously used for crops and pasture'. These surveys, conducted between 1955 and 2002, are the longest running estimates of the area of salt-affected land. They indicate that the area of salt-affected land has grown from about 73 000 to 933 000 hectares (ha; Table 1). However, only 4 surveys included all agricultural shires and the same question in comparable portions of the survey form.

Department of Agriculture (1994)

In 1994, the Department of Agriculture estimated the area of salt-affected land in the south-west agricultural area (Ferdowsian et al. 1996). The estimate was based on extrapolations from catchment-scale, aerial photograph interpretations, landholder-mapped estimates, ground-based terrain conductivity surveys and satellite remote sensing estimates of salt-affected areas. The area of salt-affected land in 1994 was estimated to be about 1.8 million hectares or 9.4% of the area cleared for agriculture (Table 1).

National Land and Water Resources Audit (2000)

The National Land and Water Resource Audit (NLWRA) identified dryland salinity as one of 7 major themes for an audit of Australia's land, water, vegetation and natural resources. The NLWRA reported areas at risk of shallow watertables as an indicator of the 'risk of salinity', based on regional-scaled soil-landscape system mapping (Short & McConnell 2001).

The definition of dryland salinity was taken to be 'the area where watertables were mapped at a regional scale to be within 2 metres of the land surface and showing no trend, or from 2 to 5m and rising'. The NLWRA estimated that about 3.55 million hectares (16%) of the south-west agricultural region was at risk of being salt-affected in 2000 (Table 1). However, the NLWRA methodology overestimated the area actually affected because not all of the area with a shallow watertable would be affected by salinity.

Land Monitor project (1988–2000)

The Land Monitor project used sequences of satellite (Landsat TM) imagery, a high resolution digital elevation model (DEM) and other spatial data to map areas of severely salt-affected land based on areas of consistently low productivity.

The project mapped severely salt-affected land over most of the dryland agricultural area of WA for 2 time periods: typically within 1988–92 and 1996–2000. The estimate of severely salt-affected agricultural land was about 860 000ha (4.6%) in 1989 and about 960 000ha (5.1%) in 1996 (Table 1). These estimates indicate the area of severely salt-affected agricultural land increased by 100 000ha over the 7 years or about 14 000 hectares per year (McFarlane et al. 2004).

This process underestimates salinity in high rainfall areas because much saline land carries permanent cover. It may also overestimate salinity in drier areas where consistently low productivity occurs for reasons other than salinity (Furby et al. 2010).

Though it is now more than 15 years old, the Land Monitor data is the most comprehensive, high resolution mapping of the extent of salinity currently available for the dryland agricultural region of WA (Caccetta et al. 2010).

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Salinity Investment Framework (2000)

Developing a Salinity Investment Framework (SIF) was commissioned by the former State Salinity Council in 2000 to guide public investment in salinity management initiatives at state, regional and catchment levels.

The Department of Agriculture conducted the SIF analysis at a state scale using soil-landscape zones to assess the impact of salinity on private and public land, and infrastructure (towns, roads, rail). The analysis revised the Land Monitor mapping results, hydrologic data and models, provided judgement (impact and potential for adopting options) and economic analyses.

Results from revised Land Monitor data indicate about 1 million hectares of land in the south-west region was affected by salinity in 1998 (Table 1). Of this, 821 000ha is agricultural and 226 000ha is public land. The SIF analysis also estimated about 250km of highways and main roads and 3850km of local and unclassified roads were affected by salinity (Sparks et al. 2006, George et al. 2005).

Table 1 Estimates of the area of salt-affected land in the south-west of WA (adapted from Raper et al.)
Date Area (ha) Source

Methods

1955

   73 000

ABS agricultural census

Landholder estimate
1962   124 000

ABS agricultural census

Landholder estimate

1979   167 000

ABS agricultural census

Landholder estimate

1984   255 000

ABS agricultural census

Landholder estimate

1989    446 000

ABS agricultural census

Landholder estimate

1989    859 000 Land Monitor project

Remotely-sensed data (Landsat TM and DEM) classification

1993    529 000

ABS agricultural census

Landholder estimate

1994 1 804 000

Conference paper

(Ferdowsian et al. 1996)

Department of Agriculture estimates based on available data and information
1996    958 000 Land Monitor project Remotely sensed data (Landsat TM and DEM) classification
2000 3 553 000 National Land and Water Resource Audit Groundwater depth and trend analysis
2002    933 000

ABS Agricultural Census

Landholder estimate

2002 1 047 000

Salinity Investment Framework: Phase I

Revised remotely-sensed data classification from Land Monitor

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For more information

See the Report card on sustainable natural resource use in agriculture Chapter 2.7 Dryland salinity.

References

Australian Bureau of Statistics 2002, Salinity on Australian farms, Bulletin 4615, ABS, Canberra.

Caccetta, D, Dunne, G, George, R & McFarlane, D 2010, ‘A methodology to estimate the future extent of dryland salinity in the southwest of Western Australia’, Journal Environmental Quality, vol. 39, pp. 26–34.

Ferdowsian, R, George, R, Lewis, F, McFarlane, D, Short, R & Speed, R 1996, ‘The extent of dryland salinity in Western Australia’, Proceedings of the 4th National Conference and Workshop on the Productive Use and Rehabilitation of Saline Lands, National Program on Productive Use and Rehabilitation of Saline Lands, Albany, Western Australia, pp. 89-97.

Furby, SL, Caccetta, PA & Wallace, JF 2010, ‘Salinity monitoring in Western Australia using remotely sensed and other spatial data’, Journal Environmental Quality, vol. 39, pp. 16–25.

George, RJ, Kingwell, R, Hill-Tonkin, J & Nulsen, R 2005, 'Salinity investment framework: agricultural land and infrastructure', Resource management technical report 270, Department of Agriculture, Western Australia.

McFarlane, DJ, George, RJ & Caccetta, PA 2004, ‘The extent and potential area of salt-affected land in Western Australia estimated using remote sensing and Digital Terrain Models’, Engineering Salinity Solutions: Proceedings of 1st National Salinity Engineering Conference, Institution of Engineers, Perth, Western Australia, pp. 55–60.

Raper, R, Speed, R, Simons, J, Kendle, A, Blake, A, Ryder, A, Smith, R, Stainer, G & Bourke, L 2014, 'Groundwater trend analysis for south-west Western Australia 2007–2012', Resource management technical report 388, Department of Agriculture and Food, Western Australia.

Short, R & McConnell, C 2001, 'Extent and impacts of dryland salinity', Resource management technical report 202, Department of Agriculture, Western Australia.

Sparks, T, George, R, Wallace, K, Pannell, D, Burnside, D & Stelfox, L 2006, Salinity Investment Framework Phase II, Western Australia Department of Water, Salinity and land use impacts series, Report No. SLUI 34, Perth.

Contact information

Richard George
+61 (0)8 9780 6296
John Simons
+61 (0)8 9083 1128
Russell Speed
+61 (0)8 9956 8561
Paul Raper
+61 (0)8 9780 6295
Page last updated: Thursday, 7 September 2017 - 1:02pm