Abstract:
Updated proxy reconstructions of water year (October-September) streamflow for
four key gauges in the Upper Colorado River Basin were generated using an
expanded tree ring network and longer calibration records than in previous
efforts. Reconstructed gauges include the Green River at Green River, Utah;
Colorado near Cisco, Utah; San Juan near Bluff, Utah; and Colorado at Lees
Ferry, Arizona.
... The reconstructions explain 72-81% of the variance in the
gauge records, and results are robust across several reconstruction approaches.
Time series plots as well as results of cross-spectral analysis indicate strong
spatial coherence in runoff variations across the subbasins. The Lees Ferry
reconstruction suggests a higher long-term mean than previous reconstructions
but strongly supports earlier findings that Colorado River allocations were
based on one of the wettest periods in the past 5 centuries and that droughts
more severe than any 20th to 21st century event occurred in the past. 
