Secondary dryland salinity has been one of Australia’s most costly forms of land degradation. Most annual crops, such as wheat, are susceptible to salinity, which reduces grain yields if it exceeds a threshold level. The assessment completed by the National Land & Water Resources Audit (NLWRA) in 2001 (NLWRA 2001) is still the most comprehensive overview of dryland salinity in Australia. Assuming no changes in water balance, the NLWRA expected dryland salinity to increase from 5.7 million hectares to 17 million hectares by 2050. However, the millennium drought appears to have halted the spread of dryland salinity in most of the worst-affected regions, especially in south-western Western Australia and Victoria; the spread is likely to increase with a return to wetter conditions. Large areas of New South Wales along the Great Dividing Range, and in the Liverpool Plains, Hunter Valley and Greater Sydney regions reported soil salinity as their main issue of concern (NSW EPA 2015).
The outlook described by the NLWRA will need further consideration if current projections for a drying of southern Australia are correct. However, the long-term outlook for more recently cleared land in the northern Murray–Darling Basin and central Queensland is unclear. Large areas are yet to reach a new hydrological equilibrium after clearing.
Given the effects of drought over the past decade, this report does not provide an update on previous SoE reports or the NLWRA assessment regarding salinity. However, close surveillance of groundwater systems is essential, particularly in regions that returned to wetter conditions in 2010–15. A key requirement for understanding the state of dryland salinity in Australia will be to maintain the groundwater monitoring network established under the National Action Plan for Salinity and Water Quality.