Crumb Trail
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Thursday, May 25, 2006
 

The Colorado river than Powell saw when he explored it for the post-bellum US in 1869 may have been more representative than the river we've seen since the turn of the century.

A new tree-ring-based reconstruction of 508 years of Colorado River streamflow confirms that droughts more severe than the 2000-2004 drought occurred before stream gages were installed on the river.

The new research also confirms that using stream gage records alone may overestimate the average amount of water in the river because the last 100-year period was wetter than the average for the last five centuries. . .

"The updated reconstruction for Lee's Ferry indicates that as many as eight droughts similar in severity, in terms of average flow, to the 5-year 2000-2004 drought have occurred since 1500."

Well, that's interesting but so what?
Allocations of Colorado River water made in the 1922 Colorado River Compact between the states of Arizona, California, Colorado, Nevada, New Mexico, Wyoming and Utah therefore overestimate the amount of river water available. Los Angeles, Las Vegas, Denver, Phoenix, Tucson and Albuquerque are among the many cities dependent on Colorado River water. . .

The underlying message from these new reconstructions remains the same: that Colorado River Compact allocations were based on one of the wettest periods in the past five centuries, and that droughts more severe than any in the last 100 years occurred before stream gages were installed. The most severe sustained drought (based on the lowest 20-year average) in the Upper Colorado River basin occurred in the last part of the 16th century. This reconstruction also shows that average annual flows on the Upper Colorado regularly vary from one decade to the next by more than 1 million acre-feet.

According to Eric Kuhn, general manager of the Colorado River Water Conservation District and an expert on Colorado River issues, "Water managers have always made critical water decisions based on a relatively short and often incomplete gaged record for the Colorado River. This study should be of keen interest because it shows that there were likely a number of long-term droughts more severe than what we experienced in the 1900s and during this century. The study should have enormous implications on how the river is managed."

This isn't new news. Previous studies decades ago said much the same, but this one is a bit more rigorous and largely confirms previous findings.

posted by back40 | 5/25/2006 03:42:00 PM

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