The Sensitivity of Mountain Snowpack Accumulation to Climate Warming

Controls on the sensitivity of mountain snowpack accumulation to climate warming (lambda(S)) are investigated. This is accomplished using two idealized, physically based models of mountain snowfall to simulate snowpack accumulation for the Cascade Mountains under current and warmed climates. Both models are forced from sounding observations. The first model uses the linear theory (LT) model of orographic precipitation to predict precipitation as a function of the incoming flow characteristics and uses the sounding temperatures to estimate the elevation of the rain-snow boundary, called the melting level (ML). The second ML model'' uses only the ML from the sounding and assumptions of uniform and constant precipitation. Both models simulate increases in precipitation intensity and elevated storm MLs under climate warming. The LT model predicts a 14.8%-18.1% loss of Cascade snowfall per degree of warming, depending on the vertical structure of the warming. The loss of snowfall is significantly greater, 19.4%-22.6%, if precipitation increases are neglected. Comparing the two models shows that the predominant control on lS is the relationship between the distribution of storm MLs and the distribution of topographic area with elevation. Although increases in precipitation due to warming may act to moderate lambda(S), the loss of snow accumulation area profoundly limits the ability of precipitation increases to maintain the snowpack under substantial climate warming (beyond 1 degrees-2 degrees C). Circulation changes may act to moderate or exacerbate the loss of mountain snowpack under climate change via impacts on orographic precipitation enhancement.