Australia: The Land Where Time Began

A biography of the Australian continent 

Groundwater Resources of southwestern Australia Potential Climate Change Impacts

According to Ali et al. about 75 % of the water used in southwestern Australia is obtained from groundwater. Since about 1975 declining rainfall and increased abstraction have had the result of declines in some groundwater levels and a decrease in health and extent of some ecosystems that are dependent on groundwater. As crops and pastures are shallow-rooted groundwater levels are rising beneath some areas that are used for dryland (rainfed) agriculture. By 2030 almost all global climate models (GCMs) are projecting a drier and hotter climate for the region. Ali et al. applied 5 climate models in this project to groundwater models in order to estimate groundwater levels in the region in 2030. The climate scenarios used were:

1.      A continuation of the historical climate of 1975-2007 until 2030;

2.      a continuation of the more recent climate 1997-2007 until 2030;

3.      climate scenarios derived by applying the GCM projected climate under global warming scenario 0.7^oC by 2030;

4.      climate scenario derived by applying the GCM projected climate under global warming scenario 1.0^oC by 2030;

5.      climate scenarios derived by applying the GCM projected climate under global warming scenario 1.3^oC and;

6.      a climate scenario considering increasing extraction levels to maximum levels allowed under a medium future climate (1.0^oC warming).

It was found that for a drier climate in the future, as well as a continuation of the climate that had been experienced since 1975, groundwater levels were affected much less than surface water resources. Recharge was highest for a fixed rainfall where there were sandy soils with little or no perennial vegetation and where the watertable was not very shallow or very deep. A feature in the project area is that about ½ of the area has a watertable within 10 m of the surface of the soil, and about ¼ within 3 m. A decline in rainfall did not affect levels as much reduced drainage of groundwater and losses to evaporation offset the reduced rainfall amounts. It was found, however, that when a threshold groundwater level is exceeded the rainfall fails to refill the seasonal storage that is available, so groundwater levels decline. Under a drier climate all areas where perennial vegetation was present and able to intercept recharge or use groundwater directly projected water tables declined. Projected groundwater levels continued to rise even under a drier future climate in areas under dryland agriculture. It is expected that climate change effects will be modest on confined groundwater systems. According to Ali et al. this is because it takes longer for the changed recharge and water level conditions to propagate from the overlying aquifers to the confined aquifers. It is projected that all water balance components will be impacted by climate change to a greater or lesser extent. Ali et al. say the result of this is that there are consequences for the amount of extractable water from confined as well as unconfined aquifers, and there are changes to the risk of the intrusion of sea water, and also for the ecosystems that are dependent on groundwater.

Sources & Further reading

1. Ali, R., D. McFarlane, S. Varma, W. Dawes, I. Emelyanova, G. Hodgson and S. Charles (2012). "Potential climate change impacts on groundwater resources of south-western Australia." Journal of Hydrology 475(0): 456-472.