Validating Canadian land surface scheme heat fluxes under subarctic tundra conditions

This study tests the ability of the Canadian Land Surface Scheme (CLASS) to simulate sensible and latent heat fluxes over two subarctic tundra sites in the Trail Valley Creek (TVC) drainage basin, North West Territories, Canada. CLASS simulations with and without the new organic soil parameterisation developed for peatland conditions were compared with three summer months of measurements at each site. The sites are located in a cryoturbated region and are underlain by continuous permafrost and feature mineral soil hummocks and organic soil inter-hummock zones. Results from the peatland version of CLASS showed significant improvement over the standard version although in both cases, there was an underestimation of latent heat fluxes and overestimation of sensible heat fluxes. The observed soil moisture contents are almost constant at both sites. Field photographs show the sites are located in low-lying areas, one in a local depression and the other at the bottom of a valley. Thus, it is reasonable to assume that the constant soil moisture content is maintained by lateral flow from adjacent hillslopes. This assumption could be further supported by the influence of mineral earth hummocks in TVC drainage basin. CLASS is a one-dimensional column model and it is not possible to explicitly represent lateral flow. Thus a nudging module is added to the peatland version of CLASS to reflect this horizontal water movement. Simulations were further improved with this modification. This additional module is a simple and effective way to represent the effect of lateral flow