Assessing the impacts of global warming on snowpack in the Washington Cascades


Casola, J.H., Cuo, L., Livneh, B., Lettenmaier, D.P., Stoelinga, M.T., Mote, P.W., Wallace, J.M. 2009. Assessing the impacts of global warming on snowpack in the Washington Cascades. Journal of Climate 22:2758-2772, doi: 10.1175/2008JCLI2612.1.


The decrease in mountain snowpack associated with global warming is difficult to estimate in the presence of the large year-to-year natural variability in observations of snow water equivalent. A more robust approach for inferring the impacts of global warming is to estimate temperature sensitivity λ of spring snowpack and multiply it by putative past and future temperature rises observed across the Northern Hemisphere.

Estimates of λ can be obtained from (a) simple geometric considerations based on the notion that as the seasonal-mean temperature rises by the amount δT, the freezing level and the entire vertical profile of snowpack should rise by the increment δT/Γ, where Γ is the mean lapse rate, (b) regression of April 1 SWE measurements upon mean winter temperatures, (c) a hydrological model forced by daily temperature and precipitation observations and (d) use of inferred accumulated snowfall derived from daily temperature and precipitation data as a proxy for snow water equivalent. All four methods yield an estimated 20% loss of spring snowpack for a 1°C temperature rise. The increase of precipitation accompanying a 1°C warming can be expected to decrease the sensitivity to 16%.

Considering various rates of temperature rise over the Northern Hemisphere, it is estimated that spring snow water equivalent in the Cascades portion of the Puget Sound drainage basin should have declined by 8-16% over the past 30 years due to global warming and it can be expected to decline by another 11-21% by 2050.