Improvements of a subcanopy snow model conveyed by observations from a mid-altitude alpine site

In the Alpine region, forests cover about 2/3 of the ground, yet surface and/or snow models designed for hydrological applications, often represent them in a very coarse way.

In the current study, we present and evaluate new developments in the physics-based ISBA/MEB-Crocus model that enables a detailed representation of snow cover and processes in interaction with an above-lying 1-layer canopy and atmosphere, and with a litter layer on top of the ground. While the canopy representation within this model demonstrated an added value for climate modeling, due to a better representation of snowpack in subarctic regions characterised by boreal forests, ISBA/MEB-Crocus failed to reproduce the observed snowpack at a mid-altitude alpine forest site, systematically overestimating the snowpack in terms of depth and duration.

With a view of correcting for these biases, we use detailed snowpack and meteorological measurements available at the Col de Porte research site in the Chartreuse massif, France, at both open and forested sites. In addition to conventional measures, indirect interception measurements and tree and soil temperatures are recorded.

The use of this dataset enables the improvement of the MEB-Crocus model for alpine forests. This enhancement is achieved through an adaptation of the interception scheme, a revision of the melt parametrization for intercepted snow, and of the unloading scheme. The meteorological forcing is also adapted to align with the top-of-canopy conditions. We demonstrate that these adjustements enable the snowpack model to replicate the observations for the Col de Porte forest site without degrading the results for Artic regions. Furthermore, we characterize the influence of the various parameters employed for the representation of the forest and their physical consistency.

This detailed, point-scale evaluation paves the way for the use of this model for distributed simulations enabling an insight into the role of snow and snow-forest interactions in the hydrological regime of mid-altitude alpine catchments.