Declining Snowpack in the West
Snow shapes the landscapes and economies of the Western United States. Snowpack generates the streamflow that allows agriculture and cities to flourish in semi-arid landscapes. The patterns of snowfall govern the distribution of glaciers and alpine meadows as well as ski resorts. We're understandably alarmed when scientists report that snowpack in the West has been steadily declining for several decades. Is this normal, that is, part of some long-term pattern of waxing and waning precipitation? Or does this portend long-term scarcity of snow in the West? To answer these questions, we need snowpack records that encompass a century or more, allowing us to assess trends and cycles in snow climate.
Our project seeks to address this gap using tree-rings to reconstruct snowpack over several centuries for three key high-mountain areas: the Upper Colorado River Basin, Upper Yellowstone/Missouri River Basin, and the Columbia and Saskatchewan River Headwaters. The resulting high-resolution maps of past snowpack will, in turn, be used to understand how ocean sea surface temperatures (e.g., El Niño, Pacific Decadal Oscillation) influence snowpack in the West. This question is particularly important in sorting out the degree to which current trends are ‘natural' vs. resulting from human-caused changes in climate. 
This project will also develop tools for water managers to assess how variability in snowpack affects resource management. Our work is particularly relevant as our three target ranges form the headwaters for the West's three most important watersheds, the Colorado, the Yellowstone/Missouri and the Columbia.
In order to calibrate tree-ring data to snowpack data, we have assembled large spatial databases using existing tree-ring chronologies and records of April 1st snow water equivalent (SWE) in the headwaters of our three target watersheds. Our preliminary results indicate that the tree-ring reconstructions faithfully capture the decade-scale variability in 20th century snowpack.
Although our research focuses on three distinct regions, the concepts and methodologies we develop will be applicable in similar settings throughout the world. The overarching goal of this project is to lay the foundation for snowpack reconstructions that encompass all the high mountain areas in western North America.
For more information see a presentation given at the 2008 Mountain Climate Meeting in Silverton, CO.
Key Collaborators:
Greg Pederson, SNRE
Lisa Graumlich, SNRE
Stephen Gray, University of Wyoming
Jacqueline Shinker, University of Wyoming
Daniel Fagre, US Geological Survey, Glacier Field Station
Connie Woodhouse, Geography Department, University of Arizona
Brian Luckman, University of Western Ontario
Emma Watson, Independent Research Scientist
Scott St. George, Canadian Geological Survey
Support from:
National Science Foundation (NSF) | Geography and Regional Science
U.S. Geological Survey (USGS) | Western Mountain Initiative
