Here's an article about the recent tree-ring study of drought in the Colorado River basin from the Arizona Daily Star. From the article, "A new UA study uses tree-ring data to reconstruct Colorado River flows over the past 500 years. The study could have a significant impact on water use in the West and further emphasizes the need for flexibility in managing the resources, according to scientists and policy experts who study the Colorado River basin. The study found several periods of more severe and longer-lasting drought than the region has experienced in the past century. The findings provide further indications that the data used for the 1922 Colorado River Compact overestimated the Colorado's average water flow, with water allocations to the seven Western states that share the river based on one of the wettest periods in the past 500 years...
"Updating the University of Arizona's groundbreaking 1976 study of tree rings in the Colorado basin, the new work reconstructed the river flows back four centuries before the gauge record and found eight periods of drought of equal or greater severity to the most recent drought, roughly from 1999 to 2004, said Dave Meko, one of the study's authors...
"The study, a collaboration between the University of Arizona's Laboratory of Tree-Ring Research, the National Oceanic and Atmospheric Administration, the U.S. Geological Survey and the University of Colorado, is published in this month's issue of Water Resources Research. While the new reconstructions estimate the average water flow at 14.6 million acre-feet, compared to the 1976 study's estimate of 13.5 million acre-feet, the longer historical average remains below the 15.2 million acre-feet recorded by stream gauges from 1906 to 1995. The researchers compared tree-ring widths from 1906 to 1995 with the stream flows recorded by gauges along the river as a way to calibrate the tree rings, then applied the statistical comparison to the tree rings dating back to the late 1400s. The core samples used in the study were taken from about 1,200 trees in 60 areas throughout the Colorado River basin. The update of the 1976 study gives more precise results, filling in gaps to provide a more accurate picture overall of the Colorado region, Meko said. The new work had 40 more years of tree-ring data to build a more accurate statistical model from comparisons to the gauge records, plus expanded tree-ring site coverage of the basin for a more reliable sample. The study zeroed in on a drought period of about 20 years in the late 1500s, a much longer drought cycle than contained in the gauge records of last century...
"The researchers are trying to reconstruct the water flows even further back into the past by expanding the tree-ring data to include core samples from dead trees, preserved pieces of trunks and standing snags known as remnant wood, Meko said. The reconstruction has reached the limit of living trees, but using the evidence from remnant wood, researchers can see growth patterns about 200 years further into the past. The wood, however, is more difficult to find and will yield a spottier record."
Category: Colorado Water
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