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Posted: March 21, 2012

Is this global warming?

Planners worry climate change is shrinking the Colorado River. Here are the numbers

Bart Taylor

Water planners in the Western United States are concerned climate change is diminishing precipitation throughout the Colorado River Basin.

The big fear is that as warming intensifies, the decline will accelerate. As a practical matter, this possibility has convinced many that significant steps need to be taken now to slow or outright halt any future development from the river or its primary tributaries, such as the Green River.

But what does the data show?  Are warming temperatures significantly diminishing river flows? Following is a look at flows in the Colorado River since 1896, measured in millions of acre-feet of water. The blue line tracks the estimated virgin flow of the river (without dams, diversions, etc.); the black line is a 10-year moving average. The data comes from the Second Annual Report of the Upper Colorado River Commission published in September 2010, provided by Jim Pokrandt, Communications & Education, Colorado River District.

A couple things jump out.

The Compact was agreed upon in 1922 during a relatively wet period in the past 100-plus years. Did Compact negotiators overestimate the amount of water in the river to divide?

The drought of the 2000’s is also evident.

But are the numbers irrefutable? After a close look, is this what a significant global warming impact looks like?

The year 2011 may also be the beginning of an above-average wet period. The historic record forecasts its inevitability.

Do the they convey an alarming drop-off that signals the beginning of consistently lower flows? It’s debatable.

Many forecast that climate change will reduce the wet years and deepen the drought periods in the years ahead. It certainly might. But the data might also show that warming has not yet had the same impact on the river as it has on ice caps and glaciers.

Bart Taylor is the publisher of ColoradoBiz magazine. E-mail him at btaylor@cobizmag.com.

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