WHAT THE PALEO-RECORD TELLS US ABOUT DROUGHT IN THE UNITED STATES: PAST AND FUTURE

Instrumental records document significant droughts in the U.S. over the past century. The most extensive drought, the 1930s Dust Bowl drought, affected up to 70% of the contiguous U.S. and caused great economic and societal losses. Other droughts, although less widespread, have also caused great devastation. Containing just a handful of major droughts, the instrumental records of the 20th century are inadequate for assessing the frequency of occurrence of these types of events. Paleoclimatic data provide a way to assess these droughts in the context of hundreds to a few thousand years. A rich network of tree-ring data in the U.S documents droughts of the past and describes a much broader range of drought variability than the length-limited instrumental data. Tree-ring based reconstructions of drought indices, streamflow, and precipitation can be used to assess temporal and spatial patterns of drought across the U.S. For example, the tree-ring records reflect no year with drought as extensive as in 1934 over the past 300 years, although droughts with coverage similar to the1950s drought have occurred quite regularly over the past centuries. In addition, persistent and widespread droughts appear to have been much more common prior to 1300. These extended records of hydroclimatic variability can have important implications for resource management. In the case of the Colorado River basin, reconstructions of streamflow indicate that the early 20th century, the period upon Colorado River allocations were based, was one of the wettest periods in the past 500 years, suggesting that the river's resources have been over-allocated. These paleo records of past drought contain valuable information on long-term natural variability, that in concert with scenarios for future climate, are necessary to anticipate and plan for droughts in the future.