Snowpack models

Sommaire

Snow is a major component of mass and energy exchanges between surface and atmosphere. It has a high albedo, a maximum temperature of 0°C and a high isolating capacity. At climatic scale, it plays a significant role on climate variability due to feedback loops, like the well-known albedo positiv feedback. At catchment scale (particularly for mountainous areas), snow stocks water during winter season and returns it to valley areas when it melts. In mountains, snow is also a source of natural and accidental hazard (avalanches).

In the framework of these different applications, the CNRM-GAME has developed a set of models to simulate some snowpack features. These models, included in SURFEX, are unidimensional, i. e. they simulate snowpack as a set of homogenous and infinite layers parallel to the ground slope. The simplest ones simulate the snowpack with a single layer on the ground. The models with an intermediate complexity include several layers to represent different types of snow close to the surface or deeper into the snowpack. The most detailed one (Crocus) deals with a larger number of layers of variable thickness (on the order of a few cm at most). This accuracy is necessary to realistically simulate a large set of physical processes at the snow surface and within the snowpack.

Crocus was initialy developed for the avalanche hazard forecasting. It is completed with the model MEPRA (which does a mechanical stabilty analysis of the snowpack simulated with Crocus) and with the meteological analysis SAFRAN (which provides meteorological data to Crocus). The three models form the SAFRAN-Crocus-MEPRA (SCM) suite, operational tool daily used by Météo-France avalanche forecasters.