541date, the impact of the drying climate on groundwater trends (diminished recharge)
is still less than the historical impact of clearing. In the future as aquifers equilibrate
to the effects of clearing, climate will be the predominant influence and the area of
salinity will respond commensurately.
In Victoria, steady rises in groundwater levels in the 1980s and early 1990s were
followed by decreases of up to 10 m after 1996 with decreases greater than the pre-
vious rises in most cases (Reid et al. 2008 ). There was evidence that the spread of
land salinisation in the state had stalled. A return to more normal rainfall conditions
in recent years has not resulted in a recovery of these levels and the salinity risk
remains low in many areas which had previously been considered at high risk.
Similarly, in New South Wales, earlier estimates of future salinity were later
considered overestimates (NSW DECC 2009 ). The rate of drainage of groundwater
in dryland agricultural catchments when the Millennium Drought hit in 1996 was
unexpected. For example, in the Liverpool Plains, it was thought that levels would
only begin to drop after 20 to 60 years were recharge to be reduced to zero (Walker
et al. 1999 ) because the discharge capacity of the monitored catchment was esti-
mated to be only 1 mm per year. Falling groundwater levels does not automatically
reclaim salt-affected areas because there is usually a need to improve soil structure
because of sodicity and to improve the ability of exposed subsoils to grow plants
given the loss of topsoils in most secondary saline areas.
Much of southern Australia which has the highest incident of dryland salinity has
experienced a drying climate in recent decades. The change in rainfall patterns is
believed to be caused by the poleward movement of climate drivers such as cold
fronts which bring rainfall in autumn to spring (Bureau of Meteorology 2014 ;
Fig. 5 Change in groundwater rising and falling trends before and after 2000 in different parts of
south-western Australia (data from George et al. 2007 )
Salinity in Dryland Agricultural Systems: Challenges and Opportunities