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Drought in the Murray-Darling Basin

Paul Tregoning¹, Marc Leblanc² and Guillaume Ramillien³

1 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
2 School of Earth and Environmental Sciences, James Cook University, Cairns, Australia.
3 Groupe de Recherche en Géodesie Spatiale, CNRS, Toulouse, France.

Figure 1. Change in water storage of the Murray-Darling Basin as estimated from a) GRACE space gravity observations b) groundwater borehole measurements c) GLDAS soil moisture model d) lake, river and reservoir level estimates (Leblanc et al., 2008).

The Murray-Darling Basin (MDB) is experiencing one of the most severe droughts in recorded history, driven by record high temperatures and several years of rainfall deficit. The multi-year drought has seen an almost complete drying of surface water resources, water that is required for agriculture and domestic use.

It has always been difficult to quantify total water storage in drainage basins because of the difficulty of measuring and monitoring water retained as soil moisture and in groundwater reservoirs. With the launch of the Gravity Recovery and Climate Experiment (GRACE) space gravity mission in 2002, it is now possible to estimate basin-scale total water storage. GRACE detects changes in the Earth's gravity field - more precisely, changes in potential between the centre of the Earth and the satellites. Making the assumption that the changes in potential are due entirely to changes in water volume, it then becomes possible to estimate the spatial and temporal variations in water integrated across large regions.

Figure 1 shows the time series of changes in total water storage of the MDB since the beginning of the GRACE mission (Leblanc et al., 2008) compared to groundwater, soil moisture and surface water variations. A significant loss of ~260 GTonnes of water can be seen between 2005 and 2007 in the GRACE estimates and the overall loss of total water storage correlates with groundwater losses. The meteorological drought (ie rainfall quantities) abated in 2007 and early 2008 with a return to average or above-average rainfall in the northern part of the basin. The drought actually began some years earlier; hence it is not possible to quantify the total loss of water caused by the current drought. Nonetheless, the GRACE total water storage data indicates that a substantial water deficit remains. Rainfall levels have declined below average values since March 2008.

Leblanc, M., P. Tregoning, G. Ramillien, S. Tweed and A. Fakes, Basin scale, integrated observations of the 21st Century multi-year drought in southeast Australia, Water Resourc.. Res. in revision.