Advances in Spatial Snow Modeling in Mountain Terrain

Snow modeling is a demanding task in itself, but is even more demanding in complex terrain such as the Rocky Mountains. Snow modeling is carried out here with the ACRU agro-hydrological modeling system. A critical advancement was the development of a new method to separate snow and rain (Kienzle, 2008). As a further improvement, a new GIS based method that determines two daily minimum and maximum temperatures, based on incoming radiation calculations and leaf area index adjustments, is presented. This results in a daily, lapse rate dependent, air temperature to determine the precipitation type (snow or rain), and a near-ground air temperature to determine snow melt and evapotranspiration rates. A drawback in most distributed hydrological models is that area calculations are based on the horizontal plane rather than the sloped area. A method is presented to use two area calculations for each hydrological response unit: a horizontal area, which is used for precipitation input calculations, and a larger sloped area, which is used for all other hydrological processes, including interception, sublimation, snow melt, soil moisture, or groundwater recharge.