Apr 19, 2017

Large near-term projected snowpack loss over the western United States

John C. Fyfe, Chris Derksen, Lawrence Mudryk, Gregory M. Flato, Benjamin D. Santer, Neil C. Swart, Noah P. Molotch, Xuebin Zhang, Hui Wan, Vivek K. Arora, John Scinocca, Yanjun Jiao
Nature Communications
  • States that although several studies have found an anthropogenic contribution to snowpack loss over the western United States, the combined influences of decadal variability and external forcing remain poorly quantified in observations and near-term projections
  • Analyzes monthly-mean (January-May) SnoTel observations in the western United States from 1982 to 2016 at 354 stations with elevations greater than 1,500 m
  • Finds that observations and reanalyses indicate there was a 10–20% loss in the annual maximum amount of water contained in western US snowpack between the 1980s and 2000s
  • Finds that 307 of the 354 stations (or about 87% of all stations) show a negative trend in annual maximum snow water equivalent (SWE), and that the maximum loss typically occurs in April
  • Shows that this loss is consistent with results from a large ensemble of climate simulations forced with natural and anthropogenic changes, but is inconsistent with simulations forced by natural changes alone
  • States that while the results from this analysis provide clear evidence of an anthropogenic influence on snowpack water storage, it is difficult to more reliably quantify the magnitude of this influence given the relatively short observational record of maximum snow water equivalent (SWEmax), the effects of underlying variability and the uncertainties inherent in our indirect estimate of the anthropogenic and natural SWEmax response
  • Projects a further loss of up to 60% within the next 30 years
  • The circles are the snow telemetry (SnoTel) network of stations utilized in this study. The red circles denote stations with negative trends in annual maximum snow water equivalent (SWEmax). The blue circles indicate stations with positive trends. Linear trends are computed from 1982 to 2010 to facilitate comparison with reanalysis-based estimates (for the period of maximum overlap between SnoTel and the four reanalysis products). All the stations plotted here are at elevations greater than 1,500 m.
  • Anomaly in non-overlapping 5-year averages of annual maximum snow water equivalent (SWEmax). Solid black is ALL ensemble-mean and grey is 10–90% range (based on 50 ALL realizations). Solid blue line is NAT ensemble mean and dashed blue lines indicate the 10 and 90% values. The ALL and NAT curves are from CanESM2. The dashed black curve is from the 35-member set of CanRCM4 simulations with ALL forcing. Pink denotes the average of four reanalyses and green is the SnoTel observations. Ensemble averages are expressed as anomalies relative to the model climatology for 1951–1980.