Tree rings tell tale of megadroughts

Analysis of tree rings in timber from the Colorado Plateau indicates that the region experienced a 60-year drought in the 12th century, a dry spell that eclipses any deficiencies in rainfall the area has suffered in the past century.

Previous reconstructions of the region’s climate using tree rings stretched back only to 1490, says Connie A. Woodhouse, a climatologist at the University of Arizona in Tucson. Those studies used data gathered from living trees, but she and her colleagues have extended that time line back to A.D. 762 by matching up the ring patterns in ancient tree trunks found throughout the upper reaches of the Colorado River. “It’s so arid that wood can remain on the landscape for hundreds of years” without rotting, she notes.

Two prolonged droughts are prominent in the new record, the researchers report in the May 28 Geophysical Research Letters. The team estimates that midway through the deeper drought, which stretched from 1118 to 1179, the flow volume in the Colorado River ran below average for 13 consecutive years. In comparison, droughts in this region during the past century have resulted in lower-than-average river flows for no more than 5 years in a row, says Woodhouse.

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