Snow measurements and modeling in sagebrush steppe

Sagebrush steppe is a dominant component of western U.S.A. landscapes. Here, winters are cold and windy. Snow distribution patterns, determined by interactions among snow, wind, topography, radiation, and vegetation (canopy height and spacing), are heterogeneous. Because snow affects plant-available water, winter ecosystem processes (e.g., decomposition), energy balance, and spectral signature, it is important to define sagebrush steppe snow and vegetation distributions. To do this, snow observations and a modeling system (MicroMet/SnowModel/SnowAssim) were used to quantify and spatially distribute snow-water-equivalent depths for the winters of 2005-06 and 2006-07. Two 1 km² study areas located in Colorado and Wyoming represented high- and low-elevation sagebrush sites, respectively. The high elevation site was dominated by taller Artemisia tridentata ssp. vaseyena shrubs (3-81 cm high; 66% cover), while the low-elevation site was predominately A. tridentata ssp. wyomingensis (3-50 cm high; 43% cover). Bi-weekly winter snow observations (nearly 40,000 total) were performed in the study areas. Model simulations employed fine-resolution (20 cm) topographic and vegetation data and local meteorological observations. Observations and simulations illustrate snow-depth variability between and within the two study areas and the roles that vegetation stature and spacing play in controlling snow depth and distribution. The high-elevation site was characterized by long-lasting and deeper snow cover; the vegetation snow-holding capacity was saturated until snowmelt in early spring. In contrast, the low-elevation site had shallower and intermittent snow cover. Understanding and quantifying the effects of snow-vegetation interactions in this widely distributed vegetation type are required to address ecosystem and remote-sensing implications of snow variability.