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A Brief History of Upper Colorado River Basin Streamflow
Woodhouse, C.A., Gray, S.T. and Meko, D.M. 2006. Updated streamflow reconstructions for the Upper Colorado River Basin. Water Resources Research 42: 10.1029/2005WR004455.

What was done
The authors generated updated proxy reconstructions of water-year streamflow for four key gauges in the Upper Colorado River Basin (Green River at Green River, Utah; Colorado near Cisco, Utah; San Juan near Bluff, Utah; and Colorado at Lees Ferry, Arizona), "using an expanded tree-ring network and longer calibration records than in previous efforts."

What was learned
Woodhouse et al. determined that the major drought of 2000-2004, "as measured by 5-year running means of water-year total flow at Lees Ferry ... is not without precedence in the tree ring record," and that "average reconstructed annual flow for the period 1844-1848 was lower." They also report that "two additional periods, in the early 1500s and early 1600s, have a 25% or greater chance of being as dry as 1999-2004," and that six other periods "have a 10% or greater chance of being drier." In addition, their work revealed that "longer duration droughts have occurred in the past," and that "the Lees Ferry reconstruction contains one sequence each of six, eight, and eleven consecutive years with flows below the 1906-1995 average."

What it means
"Overall," in the words of the three researchers, "these analyses demonstrate that severe, sustained droughts are a defining feature of Upper Colorado River hydroclimate." In fact, they conclude from their work that "droughts more severe than any 20th to 21st century event occurred in the past," meaning the preceding few centuries. Interestingly, this finding is just the opposite of what climate alarmists would have one believe, i.e., that global warming brings with it more frequent and longer lasting droughts of much greater severity. In stark contrast to this unsubstantiated climate-model-based claim, the real-world record of the USA's Upper Colorado River Basin suggests that such devastating climatic conditions are more strongly associated with the much colder temperatures that characterized the Little Ice Age.

Reviewed 27 September 2006