Comparison of methods for quantifying surface sublimation over seasonal snow covered terrain

Abstract:

Snow sublimation can be an important component of the snow-cover mass balance and there is considerable interest in quantifying the role of this process within the water and energy balance of snow-covered regions. In recent years, robust eddy-covariance instrumentation has allowed for the direct measurement of snow sublimation over snow-covered surfaces. However, eddy covariance measurements can be challenging for monitoring turbulent fluxes in snow-covered environments because of intensive data and power needs, and rigorous fetch requirements; thus, alternative methods of estimating snow sublimation are often relied upon. To evaluate the performance of alternative methods, measurements made by eddy covariance were compared to estimates of snow sublimation made by the Bowen-ratio energy-balance, bulk-aerodynamic flux, and aerodynamic-profile methods in the Colorado Rocky Mountains. Seasonal average sublimation rates measured by eddy covariance were 0.29 mm day^-1 in water year 2014 and 0.34 mm day^-1 in water year 2015, suggesting that at well exposed sites located below tree line, sublimation can account for approximately 8 – 16% of peak snow water equivalent in this region. The bulk-aerodynamic flux method exhibited the smallest bias and strongest correlation with eddy covariance, and has the simplest instrumentation requirements; thus was concluded to be the best alternative for estimating snow sublimation when eddy covariance measurements are not available. However, special care should be taken to properly assess (and calibrate) this method to avoid large flux biases as observed in this study.