A 1,200-year perspective of 21st century drought in southwestern North America

“The Southwest is in the midst of a decade-long dry period. Lower-than-normal rainfall combined with higher-than-normal temperatures (likely due to greenhouse warming) has substantially altered the region’s hydrologic conditions. From 2000-2009, the Colorado River exhibited the lowest 10-year-running-average flow of any 10-year period in the last century. A team of researchers led by Connie A. Woodhouse at the University of Arizona in Tucson examined paleo-climatic records to place this recent decade-long drought in a longer-term (1,200-year) context. Their findings, published in the December 13 online edition of the Proceedings of the National Academy of Sciences, are more than sobering: they are a call to assess risks and prepare for the worst. Woodhouse and her colleagues found that as bad as the current drought is shaping up to be, it pales (so far) in comparison to one that lasted two decades during the middle of the 12th-century–and these dry conditions, they warn, could happen again. This medieval drought was more severe, widespread, and longer lasting than any other in the Southwest over the past 12 centuries. Reconstructed Colorado River flows for the period 1146-1155 averaged just 11.5 million acre-feet (14.2 billion cubic meters) per year, 22 percent lower than the river’s average annual flow during the 20th century.” Read more...

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