An experimental streamflow reconstruction for the River Murray, Australia, 1783-1988

We present an experimental reconstruction of River Murray streamflow to assess present-day variations in the context of the past two centuries. Nine annually resolved paleoclimate proxy records from the Australasian region are used to develop a reconstruction of streamflow from 1783 to 1988. An ensemble of reconstructions is presented, providing probabilistic estimates of River Murray flows for each year back in time. The best-estimate reconstruction captures approximately 23% (50%) of annual (decadal) naturalized streamflow variability. High and low streamflow phases and their association with decadal climate variability in the Pacific are discussed. Reconstructed River Murray streamflow shows considerable variation since 1783. We estimate that there is a 2.3% chance that the 1998-2008 record low decadal streamflow deficit has been exceeded since European settlement. Stochastic simulations of the decadal variations in River Murray streamflow are computed using the paleostreamflow reconstruction to estimate model parameters. From these simulations, we estimate that the 1998-2008 streamflow deficit has an approximate 1 in 1500 year return period. As climate models are assessed relative to short instrumental records, future projections of decadal-scale variations in Murray-Darling Basin (MDB) streamflow may be inadequately represented. Given the immense socioeconomic importance of Australia's "food bowl," future paleoclimate and modeling efforts should be directed at understanding variability at this scale. This would greatly enhance our capacity to estimate regional sensitivity of the MDB's hydroclimate to further anthropogenic influences.