Those pesky tree ring scientists are at it again, spoiling a perfectly good party.
Stephen Gray and colleagues have taken a dig into runoff over the last 1,000 years on three major Colorado River tributaries, adding a new level of granular detail to something that already seemed apparent: Runoff during the 20th century, when we built all this infrastructure and farms and cities, is a bit of an anomaly in the long run, and not in a good way:
[T]hese reconstructions point to the unusual wetness of the gage period, and the potential for recent observations to paint an overly optimistic picture of regional water supplies. The future of the Upper Colorado River will be determined by a combination of inherent hydroclimatic variability and a broad range of human-induced changes. It is then essential that regional water managers, water users, and policy makers alike consider a broader range of hydroclimatic scenarios than is offered by the gage record alone.
Gray, Stephen T., Jeffrey J. Lukas, and Connie A. Woodhouse, 2011. Millennial-Length Records of Streamflow From Three Major Upper Colorado River Tributaries. Journal of the American Water Resources Association (JAWRA) 47(4):702-712. DOI: 10.1111/j.1752-1688.2011.00535.x