NOAA/WDS Paleoclimatology - North American Cordillera 1600 Year Snowpack Reconstructions

STUDY NOTES: Tree-ring based reconstructions of annual snow water equivalent (SWE) contained in drainage basins of the North American Cordillera for the last 1600 years. File name changes and location updates for tree ring data files, 8/17/2011: File co642.rwl (Anderson Ridge East) renamed wy042.rwl, File co643.rwl (Boulder Lake) renamed wy043.rwl, File co645.rwl (Fremont Lake) renamed wy045.rwl, File nm588.rwl (Beef Basin) renamed ut529.rwl and Lat-Long corrected, File nm589.rwl (Harmon Canyon) renamed ut530.rwl and Lat-Long corrected, Lat-Long corrected for co644.rwl, Species corrected for co650.rwl (PSME to PIED). No ring width data or climate reconstructions were affected. Composite April 1 SWE reconstruction built using "standard" chronologies (i.e. autocorrelation preserved), and extended using successively longer versions of the reconstruction that have had their mean and variance scaled to equal the "best" reconstruction. Watershed or HUC(6) six digit code corresponding with U.S. Geological Survey Hydrologic Units available for download on the U.S. Geological Survey's National Map (http://nhd.usgs.gov/data.html), and the National Atlas (http://www.nationalatlas.gov/)
ABSTRACT SUPPLIED BY ORIGINATOR: In western North America, snowpack has declined in recent decades, and further losses are projected through the 21st century. Here, we evaluate the uniqueness of recent declines using snowpack reconstructions from 66 tree-ring chronologies in key runoff-generating areas of the Colorado, Columbia, and Missouri River drainages. Over the past millennium, late 20th century snowpack reductions are almost unprecedented in magnitude across the northern Rocky Mountains and in their north-south synchrony across the cordillera. Both the snowpack declines and their synchrony result from unparalleled springtime warming that is 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 United States.