Tree-ring reconstructed streamflow and drought history for the Bighorn River Basin, Wyoming

Abstract

Predictions made by climate models suggest that in the coming decades the western United States will experience warmer temperatures, as well as changes in streamflow patterns. To better understand how climatic variability affects water resources and to critique current water-supply assumptions, water-resource management can benefit from proxy-based paleoclimatic information. Instrumental records of precipitation, streamflow, and snowpack are typically less than 100 years long and usually only capture a subset of the full range of hydrologic variability possible in a given watershed. This study presents water-year streamflow reconstructions for six gages in the Bighorn River Basin in Wyoming and Montana. The reconstructions are based on tree-ring data from various locations in the Northern Rocky Mountain region. The streamflow reconstructions are between 500 and 800 years long. Calibration models between the tree-ring data and the gage record explain up to 60% of the variation in gaged streamflow. Analysis of the reconstructions indicates that the 20th century was relatively wet compared with previous centuries, and recent droughts were matched or exceeded (in duration and magnitude) many times during the last 800 years. Pre-instrumental droughts also show strong spatial coherence across the entire Bighorn River watershed. These reconstructions can be used to develop more-robust water-management plans that take into account a broader range of conditions than those presented by gage records alone.