Reliable flow-gauge records for the Colorado River extend back to 1906. But specialists have used tree rings to estimate flows more than 1,100 years earlier, as far back as 762 A.D.
The current drought began in 2000, and is now entering its 14th year. When matched up against every other 14-year period since 762 A.D., it falls in the driest 2 percent of all those periods.
That means the current 14-year period is, as federal Bureau of Reclamation head Michael Connor told a Senate committee this summer, "one of the lowest in the Basin in over 1,200 years."
That's true, says Jeff Lukas, with the Western Water Assessment at the University of Colorado, adding that the tree rings show a half-dozen decade-or-longer droughts that were likely more severe than the current one.
But stay tuned: If the drought continues, it will likely keep climbing in the rankings.