Development of the SnowFrost model for the simulation of snow fall and soil frost

In the process of studying how climatic changes will influence important forage crops at high latitudes, van Oijen et al. (2005) developed a plant model for two grass species, timothy (Phleum pratense L.) and perennial ryegrass (Lolium perenne L.). In order to study winter survival of the plants, the plant model requires routines to simulate winter conditions, such as snow accumulation, soil frost, ice cover and soil temperature. This report describes the development of the SnowFrost model that simulates snow accumulation and the formation of soil frost. Routines for simulating ice encasement will be added at a later stage. The SnowFrost model implements a degree-day-temperatureindex method in the snowmelt routines, and an energy balance approach to get an algebraic expression for soil frost formation. Our main focus when developing the winter model is to adequately simulate winter conditions from the plant's point of view, rather than accurately simulate the depths of snow cover and soil frost penetration. Simulations for a site with cold and stable winter conditions show promising results, and indicate that SnowFrost is suitable as a foundation for the continuing work of developing the winter routines for the plant model.