Upper Green River Basin (United States) Streamflow Reconstructions

The Upper Green River represents a vital water supply for southwestern Wyoming and Upper/Lower Colorado River Compact states. Rapid development in the southwestern United States combined with the recent drought has greatly stressed the water supply of the Colorado River system, and concurrently increased the interest in long-term variations in streamflow. The current research developed six new tree-ring chronologies in and adjacent to the Upper Green River Basin (UGRB). Nine proxy reconstructions (three main-stem streams and six headwater streams) of UGRB streamflow were created by combining these new tree-ring chronologies with existing tree-ring chronologies from sites adjacent to the UGRB. All UGRB streamflow reconstructions extended back to the year 1615 or earlier. The variance explained (r(2)) by these reconstructions ranged from a low of 0.44 at one headwaters gauge to 0.65 for the lowest main-stem gauge in the drainage. An extended reconstruction of the main-stem Green River gauge near Greendale, Utah extends back to 1439. As a group, the nine reconstructions show that strong regional coherency in interannual flow variability and multiyear to decadal flow regimes are consistent features of the preinstrumental period. Focusing on the Green River at Greendale reconstruction, our analyses point to unusual wetness in the 20th century and a regional hydroclimate characterized by inherent nonstationarity. Overall, these results suggest that instrumental records capture a relatively small subset of potential streamflow variability in the UGRB.