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<br />As you can see by Figure VI-I, there are a number of25 year valleys when the flow dropped <br />to 13 maf or less. 13 maf/year is an important trigger, even at today's level of demands, a 25 year <br />period with a natural flow of only 13 maf/year will draw down system storage and stress the system <br />in a major way. The lowest 25 year periods in the 1900s are all greater than 13 maf/year. . <br /> <br />Global Warming. Climate Change and the Colorado River Future Hydrology <br /> <br />Author's Note: Global warming and climate change have become a political and public <br />policy hot potato. My observation is that it has become too polarized. For some it is cause-celeb, <br />and for others, it is a hoax. The National Academies of Sciences reports that it is a real issue and <br />concern. Within the Colorado River Basin, we need to begin to consider the potential consequences <br />now. Water decisions, both for projects and operational criteria are long lasting. It may be too late <br />before we know whether the science is right or wrong, so we need to expand our planning horizon <br />to seriously consider the issues raised and a broad range of possible futures. We need to consider <br />how to avoid unacceptable outcomes, not just plan for the most probable or most politically popular. <br /> <br />The idea that global warming could reduce the stream flows in the Colorado River is not new. <br />John Carlson mentions it in his 1986 paper. According to Western Water Assessment, there have <br />been at least ten studies of the Colorado River since 1979.157 <br /> <br />Most recently a number of professional journals have addressed the matter. The <br />January/F ebruary 2007 edition of "Southwest Hydrology Magazine" has a cover titled "Inconvenient <br />Hydrology." The edition includes articles on climate change and the Colorado River. The A WRA <br />Journal "Water Resources Impact" dedicated its July 2004 and September 2006 editions to climate <br />change issues. <br /> <br />Increasing Temperatures <br /> <br />There seems to be no debate in the science community that temperatures in the Colorado <br />River Basin have increased by at least 2 Y2 0 F (1.50 C) over the last century. Figure VI-2 shows the <br />annual average surface temperature for the Colorado River Basin. The graph also shows actual and <br />modeled Colorado River Basin stream flows. The modeled stream flows are based on the Heorling <br />and Eicheid study. The Hoerling and Eicheid study suggests a drier future than other studies. <br /> <br />157Western Water Assessment is ajoint program of NOAA and the University of Colorado. See www.Colorado.edu. <br /> <br />Page -70- <br />