Climatic Change

, Volume 112, Issue 3, pp 997-1014

First online:

Impacts of climate change on August stream discharge in the Central-Rocky Mountains

  • Jason C. LeppiAffiliated withNumerical Terradynamic Simulation Group (NTSG), College of Forestry and Conservation, University of Montana Email author 
  • , Thomas H. DeLucaAffiliated withSchool of Environment Natural Resources, and Geography, 2nd Floor Environment Centre Wales, Bangor University
  • , Solomon W. HarrarAffiliated withDepartment of Mathematical Sciences, University of Montana
  • , Steven W. RunningAffiliated withNumerical Terradynamic Simulation Group (NTSG), College of Forestry and Conservation, University of Montana

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In the snowmelt dominated hydrology of arid western US landscapes, late summer low streamflow is the most vulnerable period for aquatic ecosystem habitats and trout populations. This study analyzes mean August discharge at 153 streams throughout the Central Rocky Mountains of North America (CRMs) for changes in discharge from 1950–2008. The purpose of this study was to determine if: (1) Mean August stream discharge values have decreased over the last half-century; (2) Low discharge values are occurring more frequently; (3) Climatic variables are influencing August discharge trends. Here we use a strict selection process to characterize gauging stations based on amount of anthropogenic impact in order to identify heavily impacted rivers and understand the relationship between climatic variables and discharge trends. Using historic United States Geologic Survey discharge data, we analyzed data for trends of 40–59 years. Combining of these records along with aerial photos and water rights records we selected gauging stations based on the length and continuity of discharge records and categorized each based on the amount of diversion. Variables that could potentially influence discharge such as change in vegetation and Pacific Decadal Oscillation (PDO) were examined, but we found that that both did not significantly influence August discharge patterns. Our analyses indicate that non-regulated watersheds are experiencing substantial declines in stream discharge and we have found that 89% of all non-regulated stations exhibit a declining slope. Additionally our results here indicate a significant (α ≤ 0.10) decline in discharge from 1951–2008 for the CRMs. Correlations results at our pristine sites show a negative relationship between air temperatures and discharge and these results coupled with increasing air temperature trends pose serious concern for aquatic ecosystems in CRMs.