The Unusual Nature of Recent Snowpack Declines in the North American Cordillera

This report from the U.S. Geological Survey (USGS) analyzes late-20th century snowpack reductions data to support findings that snowpack in the Western regions of North America has been declining since 1950. The data suggests that snowpack declines in the Rocky Mountains over the last 30 years are unusual compared to the past few centuries.

The report concludes that snowpack declines and their synchrony result from unprecedented springtime warming due to positive reinforcement of the anthropogenic warming by decadal variability. The increasing role of warming on large-scale snowpack variability and trends foreshadows fundamental impacts on streamflow and water supplies across the western U.S. Additional warming-induced snowpack declines, combined with increasing water demand, could threaten many current water storage and allocation strategies and lead to substantial strain on related infrastructure and overall supplies.

USGS scientists, with partners at the Universities of Arizona, Washington, Wyoming, and Western Ontario, evaluated the recent declines using snowpack reconstructions from 66 tree-ring chronologies, looking back 500 to more than 1,000 years. The network of sites was chosen strategically to characterize the range of natural snowpack variability over the long term, and from north to south in the Rocky Mountains. Tree-ring analysis allowed researchers to reconstruct snowpack over several centuries for three key high-mountain watersheds: the Upper Colorado River basin, the Upper Missouri River basin, and the headwaters of the Columbia River. Snowpack reconstructions were produced at multiple watershed scales  and the resulting high-resolution maps offered insights into natural controls on snowpack variability linked to changes in the Pacific Ocean basin (e.g., El Niño, Pacific Decadal Oscillation). This work is particularly relevant because the three target regions form the headwaters for the West's three most important watersheds.


The study, The unusual nature of recent snowpack declines in the North American Cordillera, is online at Science magazine




Publication Date: June 9, 2011

Authors or Affiliated Users:

  • Greg Pederson
  • Stephen Gray
  • Connie Woodhouse
  • Lisa Graumlich
  • Daniel B. Fagre
  • Julio Betancourt
  • Jeremy Littell
  • Brian Luckman
  • Emma Watson
  • Dave Meko
  • Troy Knight

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Resource Category:

Resource Types:

  • Assessment


  • Water supply
  • Air temperature
  • Permafrost melt
  • Precipitation changes

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