Environmental Monitoring and Assessment

, Volume 185, Issue 1, pp 719–728 | Cite as

Climate change or climate cycles? Snowpack trends in the Olympic and Cascade Mountains, Washington, USA



Climate change could significantly influence seasonal streamflow and water availability in the snowpack-fed watersheds of Washington, USA. Descriptions of snowpack decline often use linear ordinary least squares (OLS) models to quantify this change. However, the region’s precipitation is known to be related to climate cycles. If snowpack decline is more closely related to these cycles, an OLS model cannot account for this effect, and thus both descriptions of trends and estimates of decline could be inaccurate. We used intervention analysis to determine whether snow water equivalent (SWE) in 25 long-term snow courses within the Olympic and Cascade Mountains are more accurately described by OLS (to represent gradual change), stationary (to represent no change), or step-stationary (to represent climate cycling) models. We used Bayesian information-theoretic methods to determine these models’ relative likelihood, and we found 90 models that could plausibly describe the statistical structure of the 25 snow courses’ time series. Posterior model probabilities of the 29 “most plausible” models ranged from 0.33 to 0.91 (mean = 0.58, s = 0.15). The majority of these time series (55 %) were best represented as step-stationary models with a single breakpoint at 1976/77, coinciding with a major shift in the Pacific Decadal Oscillation. However, estimates of SWE decline differed by as much as 35 % between statistically plausible models of a single time series. This ambiguity is a critical problem for water management policy. Approaches such as intervention analysis should become part of the basic analytical toolkit for snowpack or other climatic time series data.


Snow water equivalent Intervention analysis Climate cycles Climate change Olympic Mountains Cascade Mountains 

Supplementary material

10661_2012_2587_MOESM1_ESM.doc (3.2 mb)
ESM 1 (DOC 3277 kb)


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Copyright information

© Springer Science+Business Media B.V. 2012

Authors and Affiliations

  1. 1.Western Washington University, Huxley College of the Environment-PeninsulasPort AngelesUSA
  2. 2.Olympic National ParkPort AngelesUSA
  3. 3.Measurement and Analytics, Group HealthSeattleUSA

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