Observations and modeling of turbulent fluxes during melt at the shrub-tundra transition zone 1: point scale variations

Vegetation has a significant influence on snow accumulation and energy availability for snowmelt. This is particularly true in the vicinity of the arctic treeline, characterized by the alternation of shrub-tundra and open-tundra, with the former expected to spread more and more. This work considers the time variation in turbulent fluxes over two open-tundra and shrub-tundra sites, where measurements of sensible and latent heat fluxes over the canopy are available. An improved version of the GEOtop hydrological model with a dual-layer surface scheme has been used to interpret and reproduce the measurements. The model allows us to separate the contribution of the vegetation and the surface to the turbulent fluxes measured above the canopy and, despite some issues related to the parameterization of the turbulence in the canopy, is able to reasonably reproduce the turbulent fluxes measured above the vegetation and the snowmelt acceleration observed in the shrub-tundra. The maximum energy contribution to the surface during snowmelt is found to occur for values of the leaf and stem area index around 1.0. The model proves to be a valuable platform to be applied in a distributed model to predict the spatial variability of snowmelt and surface energy balance.