DENDROCHRONOLOGY-BASED RECONSTRUCTION OF STREAMFLOW FOR ASHLEY CREEK AND WHITEROCKS RIVER, UINTA MOUNTAINS, NORTHEASTERN UTAH

Three long, continuous tree-ring records that were collected from the southern Uinta Mountains in 1972 (World Data Center for Paleoclimatology; Investigators: Harsha, Stockton, and Jacoby) have been used to reconstruct local mean annual discharge. The oldest of the three records dates to A.D. 1424, and was collected from Pinus edulis (pinyon pine); the younger two records date to A.D. 1636 and 1731, and were collected from Pseudotsuga menzeisii (douglas fir). Climatologic data (precipitation and temperature) for the Uinta Mountains are of limited duration; stream gage data for the same area have been continuously collected for a much longer period. These tree-ring chronologies were therefore employed to reconstruct mean annual discharge on nearby Whiterocks River and Ashley Creek for the period of record via multiple linear regression equations. During the period of overlap between the dendrochronologic records and the historic gage records (1930-1972 and 1915-1972, respectively, for Whiterocks River and Ashley Creek), the regression equations exhibit significant ability to predict streamflow as indicated by the Adjusted R² (> 0.60) and the reduction-of-error statistic (+0.60 and +0.62). The regression equations also show significant ability to predict extremely wet and dry years from the period of overlap.

The results indicate that while mean annual discharge has been decreasing on these streams since the beginning of the gage records, the 20^th Century does not contain either minimum or maximum mean annual discharge values compared to the ~350 years of reconstruction. Additionally, streamflow during the Little Ice Age period does not appear to be greater than the long-term average. This corroborates independent evidence for minimal glacial activity in the Uinta Mountains during the Little Ice Age. These reconstructed streamflow records for Whiterocks River and Ashley Creek are believed to be representative of the south flank of the Uinta Mountains because of the high correlation between contemporary annual discharges on the various streams in the range.