Parametrization of peatland hydraulic properties for the Canadian Land Surface Scheme

A hydraulic parametrization is developed for peatland environments in the C anadian Land Surface Scheme (CLASS). Three wetland soil classes account for the typical variation in the hydraulic characteristics of the uppermost 0. 5 m of organic soils. Review of the literature reveals that saturated hydra ulic conductivity varies from a median of 1.0 x 10(-7)m/s in deeply humifie d sapric peat to 2.8 x 10(-4) m/s in relatively undecomposed fibric peat. A ver age pore volume fraction ranges from 0.83 to 0.93. Parameters have been designed for the soil moisture characteristic curves for fibric, hemic and sapric peat using the Campbell (1974) equation employed in CLASS, and the van Genuchten (1980)formulation. There is little differance in modelled soi l moisture between the two formulations within the range of conditions norm ally found in peatlands. Validation of modelled water fable depth and peat temperature is performed for a fen in northern Quebec and a bog in north-ce ntral Minnesota. The new parametrization results in a more realistic simula tion of these variables in peatlands than the previous version of CLASS, in which unrealistic mineral soil "equivalents" were used for wetland soil cl imate modelling.