A New, Two-layer Canopy Module For The Detailed Snow Model SNOWPACK

Thursday, 18 December 2014
Isabelle Gouttevin1,2, Michael Lehning1,3, Tobias Jonas3, David Gustafsson4,5 and Meelis Mölder6, (1)EPFL Swiss Federal Institute of Technology Lausanne, Lausanne, Switzerland, (2)IRSTEA Lyon, Hydrology-Hydraulics, Villeurbanne Cedex, France, (3)SLF / WSL, Davos Dorf, Switzerland, (4)Swedish Meteorological and Hydrological Institute, Research and Development, Norrköping, Sweden, (5)KTH Royal Institute of Technology, Land and water resources engineering, Stockholm, Sweden, (6)Lund University, Physical geography and Ecosystem science, Lund, Sweden
A new, two-layer canopy module with thermal inertia for the detailed snow model SNOWPACK is presented. Compared to the old, one-layered canopy formulation with no heat mass, this module now offers a level of physical detail consistent with the detailed snow and soil representation in SNOWPACK. The new canopy model is designed to reproduce the difference in thermal regimes between leafy and woody canopy elements and their impact on the underlying snowpack energy balance. The new model is validated against data from an Alpine and a boreal site.
Comparisons of modelled sub-canopy thermal radiations to stand-scale observations at Alptal, Switzerland, demonstrate the improvements induced by our new parameterizations. The main effect is a more realistic simulation of the canopy night-time drop in temperatures. The lower drop is induced by both thermal inertia and the two-layer representation. A specific result is that such a performance cannot be achieved by a single-layered canopy model.
The impact of the new parameterizations on the modelled dynamics of the sub-canopy snowpack is analysed and yields consistent results, but the frequent occurrence of mixed-precipitation events at Alptal prevents a conclusive assessment of model performances against snow data.
Without specific tuning, the model is also able to reproduce the measured summertime tree trunk temperatures and biomass heat storage at the boreal site of Norunda, Sweden, with an increased accuracy in amplitude and phase.
Overall, the SNOWPACK model with its enhanced canopy module constitutes a unique (in its physical process representation) atmosphere-to-soil-through-canopy-and-snow modelling chain.