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A Half-Millennial Record of Rainfall and Runoff in Northwest Australia

Paper Reviewed
Verdon-Kidd, D., Hancock, G.R. and Lowry, J.B. 2017. A 507-year rainfall and runoff reconstruction for the Monsoonal North West, Australia derived from remote paleoclimate archives. Global and Planetary Change 158: 21-35.

Noting that "future changes to rainfall regimes remain uncertain due to the inability of Global Climate Models to adequately capture the tropical weather/climate processes that are known to be important for the Monsoonal North West (MNW) region of Australia," Verdon-Kidd et al. (2018) set out to develop a long-term rainfall and runoff reconstruction for this region that would represent a much more realistic (and full) range of climatic variability than what is noted in the brief instrumental rainfall record. The resultant chronologies were reconstructed using six proxy records and are depicted in the figure below.

As seen in the figure, noteworthy periods of below average rainfall and runoff include 1470-1650, 1780-1880 and 1920-1950, whereas above average epochs occurred in 1650-1700, 1880-1920, and the most recent 20 years of the record. However, the take-home message is that both proxies display episodes of longer and more intense wet and dry periods than are observed in the modern instrumental record. Accordingly, Verdon-Kidd et al. report that "the maximum number of consecutive years of below (above) average rainfall is 90% (40%) higher in the rainfall reconstruction than during the instrumental period." Consequently, the authors conclude that the likelihood of underestimating both flood and drought risk is high, based upon instrumental data alone.

In light of such findings, it is clear that the modern rise in atmospheric CO2 has likely had no measurable impact on MNW rainfall and runoff. Modern values of these parameters have been frequently eclipsed (by 15-20% in magnitude) across the long-term half-millennial record. And that reality (one would think) should restrain any climate-alarmist attempt to link any modern rainfall/runoff events or trends in this region with CO2-induced global warming.

Figure 1. A 507-year reconstruction of (a) rainfall and (b) runoff for the Moonsoonal North West region of Australia. Source: Verdon-Kidd et al. (2017).

Posted 12 October 2018