THE TREEFLOW PROJECT: USING TREE-RING DATA TO PROVIDE WATER MANAGERS WITH A MULTI-CENTURY PERSPECTIVE ON DROUGHT

Water resource management in the western US requires knowledge of hydroclimatic variability in order to plan for adequate water supplies during periods of drought. There is now growing appreciation among water managers that the relatively short (<100 years) instrumental records of climate and streamflow do not capture the full range of natural hydroclimatic variability, particularly extreme drought events. This became especially evident during the 2002 drought in Colorado, which resulted in the lowest flow on record at many gages.

Gage records can be extended using proxy data, and tree-ring data have proven particularly useful for this purpose. Both annual tree growth and water year runoff are strongly influenced by variations in precipitation and evapotranspiration. Thus, the annual rings of moisture-sensitive trees can be used to reconstruct streamflow records back in time 300-800 years. This longer window onto past hydroclimatic conditions is more likely to capture the full range of natural variability and provide more robust information about drought occurrence. The TreeFlow Project is a collaboration with water providers to provide tree-ring data specific to the provider's needs. We have developed a network of 80 moisture-sensitive tree-ring chronologies, which since 2002 we have used to generate over 30 multi-century streamflow reconstructions for gages critical to water management in the Colorado, Rio Grande, and South Platte River basins. Our partners are using the reconstructions in a variety of ways, including incorporating them into water system models to test their system's ability to perform under a broader range of conditions (i.e., more severe and persistent droughts) than contained in the 20th century gage records. We have made these streamflow reconstruction data publicly accessible via the project website (http://www.ncdc.noaa.gov/streamflow/) which also provides guidance for interpreting the data and a tutorial explaining the reconstruction methodology. Our current efforts include expanding the geographic scope of the project to cover the western U.S., in collaboration with other tree-ring scientists and water managers in the region.