Paper Reviewed
Ho, M., Kiem, A.S. and Verdon-Kidd, D.C. 2015a. A paleoclimate rainfall reconstruction in the Murray-Darling Basin (MDB), Australia: 2. Assessing hydroclimatic risk using paleoclimate records of wet and dry epochs. Water Resources Research 51: 8380-8396.

Using an existing network of paleoclimate rainfall proxies, and building upon the findings of a companion paper of theirs (Ho et al. 2015b), Ho et al. (2015a) constructed a pre-instrumental rainfall history of the Murray-Darling Basin (MDB) that spanned the period of time from 749 BC to 1980 AD. And this work demonstrated, as they describe it, "the need to develop additional reconstructions and, with the companion paper, demonstrate how this information can be used to benefit water resource management."

As an example of how their study answers this need, Ho et al. report that it "shows that prior to the twentieth century, both dry and wet epochs have persisted for longer periods than observed in the instrumental record," with "the probability of both dry and wet periods exceeding a decade at least 10 times more likely prior to 1883 than suggested by the instrumental records." And noting that "the instrumental record does not cover the full range of hydroclimatic variability possible in the MDB," they conclude that "hydroclimatic risk assessments based on the instrumental record likely underestimate, or at least misinterpret, the frequency, duration and magnitude of wet and dry epochs."

Consequently, if either the frequencies, durations or magnitudes of either dry or wet periods in the MDB were to significantly increase sometime in the future, these changes would be neither unusual, unprecedented nor unnatural. And there would be no rational for claiming they were caused by the concomitant upward trend in the air's CO2 concentration.

Reference
Ho, M., Kiem, A.S. and Verdon-Kidd, D.C. 2015b. A paleoclimate rainfall reconstruction in the Murray-Darling Basin (MDB), Australia: 1. Evaluation of different paleoclimate archives, rainfall networds, and reconstruction techniques. Water Resources Research 51: 10.1002/201 5WRO17058.