FORT COLLINS, Colo., Feb. 17, 2015 – A new study, A millennium-length reconstruction of Bear River stream flow, Utah,published in the Elsevier Journal of Hydrology, provides important information regarding the eastern Great Basin’s most significant water source for agricultural, urban and wildlife purposes. USDA Forest Service Rocky Mountain Research Station scientist Robert “Justin” DeRose led the team of scientists for this study.
DeRose and scientists from Brigham Young, and Utah State, developed a 1200-year Bear River stream flow record using dendroclimatology, a process that reconstructs records of past climates and climatic events by analysis of tree-ring growth characteristics.
Scientists found that they could effectively reconstruct the Bear River stream flow from the existing 67-year (1943-2010) instrumental record to a 1200-year reconstruction by focusing on living and dead Utah juniper. The oldest living Utah juniper dated back to 1426 (587 years old). “This is the first study to use the Utah juniper and also the first millennium-length reconstruction for the Wasatch Front,” DeRose said.
DeRose and others worked closely with water managers along the Wasatch Front during the study to provide information to help augment water planning. Scientists specifically correlated the Bear River gage to all lower Bear River gages to show the relationships between the reconstructed headwater portion of the river and any lower portion. Provision of the extensive historical information on stream flow variability not only illuminates possible hydrologic extremes, but when compared to annual reconstructions, it can also reveal potential effects on stream flow variability associated with long-term, severe dry and wet periods.
The Bear River contributes more water to the eastern Great Basin (northern Utah and portions of southeast Idaho and southwest Wyoming) than any other river system. It is also the cornerstone for supplying water for the future growth of the Wasatch Front metropolitan area in northern Utah.
Key findings in this study include:
The mean annual stream flow for the Bear River was 11 percent lower than the mean over the instrumental period.
The millennium-length (800-2010) reconstruction allowed the discovery of previously unknown low-frequency variability in stream flow, which gives scientists the ability to explore slow changes in climate drivers that occur over very long time periods of 150-200 years.
Only 2 of the 30 most extreme dry years occurred during the settlement era (1849 onward), while 7 of the 30 wettest years occurred within this same time period.
When analyzed over multi-year time periods, the most prolonged drought occurred during the 70-year period from 1210-1281, which roughly corresponds to the Medieval Warm Period.
The latter half of the 20th century was the second wettest multi-year period of the 1200-year reconstruction.
The climate drivers affecting the delivery of precipitation to the Bear River headwaters originate from the western Pacific warm water region, not the conventional El Niño/La Nina region.
The Rocky Mountain Research Station Inventory and Analysis program, Wasatch Dendroclimatology Research Group, US-DOI Bureau of Reclamation, and the Utah State University Agricultural Experiment Station provided funding for this project.
A copy of the study is available to download at http://www.treesearch.fs.fed.us/pubs/47621.
The Rocky Mountain Research Station (RMRS) is one of seven units within the U.S. Forest Service Research and Development. RMRS maintains 14 field laboratories throughout a 12-state territory encompassing parts of the Great Basin, Southwest, Rocky Mountains, and the Great Plains. RMRS also administers and conducts research on 14 experimental forests, ranges and watersheds and maintains long-term research databases for these areas. While anchored in the geography of the West our research is global in scale. To find out more about the RMRS go to www.fs.fed.us/rmrs. You can also follow us on Twitter at www.twitter.com/usfs_rmrs.
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