Stable water isotopes as tools for basin-scale water cycle: Diagnosis of the Murray-Darling

We examine the hypothesis that isotopic techniques are applicable to hydrological predictions in difficult-to-simulate semi-arid basins, using the Murray-Darling Basin as an example. Isotopic data from three aquifers in the Murray-Darling characterize precipitation intensity for evaluation of GCMs. Applying these to 'good' (water conserving) and 'poor' (non-water-conserving) climate model simulations of the Murray-Darling gives rise to large differences in rainfall amount (30-62%). Selecting only 'good' models shows a greater than 150 mm annual groundwater recharge loss in El Niño cf. La Niña climates. 2002-2003 El Niño drought data are used to refine isotopic calculation of water lost in evaporation from rivers and irrigation, giving a cumulative loss of 64% of river water during 2002 (cf. 80% using a previous method). This substantiates recent identification of this El Niño drought as evaporatively most extreme and we conclude that stable water isotopes, used synergistically with hydro-climate models, have great potential in future water resource predictions.