An Evaluation of High-Resolution Regional Climate Model Simulations of Mountain Snow Cover and Albedo (With Implications for the Simulated Snow-Albedo Feedback)

The snow-albedo feedback (SAF) strongly influences climate over mountainous regions in the mid-latitudes. However, the skill of regional climate models (RCMs) at simulating snow cover, surface albedo, and the SAF in these regions is poorly characterized. These features are evaluated in a pair of 7-year long high-resolution RCM simulations with the Weather Research and Forecasting (WRF) model over the central Rocky Mountains. Key differences between the configuration of the simulations include their computational domain (regional vs. continental) and the land surface model (LSM) used (Noah vs. Noah-MP). Simulations are evaluated against high-resolution satellite estimates of snow cover and albedo from the Moderate Resolution Imaging Spectroradiometer (MODIS).

Both simulations generally capture the observed seasonality of snow cover and the influence of topographic features, but also exhibit important biases. For instance, a substantial over-prediction of sub-pixel fractional snow cover when using the Noah LSM causes large positive biases in surface albedo, likely due in part to the lack of explicit representation of canopy effects. Surface measurements reveal large positive biases in snow albedo during the late spring caused by neglecting the radiative effects of impurities deposited onto snow.

Results from semi-idealized climate change experiments show substantially different magnitudes and patterns of SAF-enhanced warming in the two simulations that can be tied to the differences in snow cover in their control climates. More-confident projections of regional climate change over mountains will require further work to evaluate and improve representation of snow cover and albedo in RCMs.