Reconstructed Flows of the Logan River, Utah

Population centers in semi-arid northern Utah are dependent upon snowpack in nearby mountains for water supply. However, predicting annual snowfall is hindered by the complex teleconnections with Pacific Ocean conditions such as the Pacific Decadal Oscillation and El Niño Southern Oscillation. Tree-ring series collected from moisture sensitive sites in northern Utah can be used to extend stream discharge records and provide water managers with a longer record of variability in water supply. However, there are no published tree-ring reconstructions and few chronologies in northern Utah. This project provides reconstructed streamflows of the Logan River, a tributary of the Bear River, in northern Utah, by creating and analyzing multiple Douglas-fir (Pseudotsuga menziesii), limber pine (Pinus flexus) and rocky mountain juniper (Juniperus scopulorum) tree-ring chronologies from moisture sensitive sites at differing elevations in the Bear River Range. The relationship between tree-rings and climate were analyzed by comparing tree-ring growth to annual precipitation (snowpack), which is directly related to mean annual flow (R2 = 0.70) in the Logan River catchment. Tree-ring chronologies from similar climatic zones were accessed from the International Tree-Ring Data Bank and included in the analysis to better capture regional climate patterns. Constructed and acquired tree-ring indices were used to reconstruct streamflows of the Logan River during the last 200 to 300 years using regression analysis. Results suggest hydrologic drought and excess moisture have multi-decadal to centennial scale periodicity and that annual extremes of similar magnitude to those recorded in the instrumental record have occurred with greater frequency in the past