The Canadian Land Surface Scheme (CLASS) was tested by comparing its simulated soil water contents withthose measured from two potato sites in the Qubec City region for the growing season of 1993. Being a physically basedmodel, most of CLASS input parameters can be either measured or obtained from the literature. However, in thesimulation of soil water contents, CLASS was found to be sensitive to one particular soil texture empirical parameter, b,which is used to define the unsaturated soil hydraulic conductivity and soil water retention functions. Therefore, someadjustment of this parameter was done. To improve the performance of CLASS for the entire season, a new evaporationmodel over bare soil was introduced and its performance was clearly superior to that of the standard Philips model. Withthe adjusted b values and the new evaporation model, the values of mean bias error (MBE) of soil water content(averaged for the two sites) were 0.09% by volume for the depth of 0 to 0.45 m and 0.02% by volume for the depth of 0to 0.90 m, respectively. The corresponding values of mean absolute error (MAE) were 1.39 and 0.96% by volume. Theseerrors were considerably less than those obtained with two other models (SWACROP and SUBSTOR) using the same dataset. These models had MAE values of 2.4 and 2.8% by volume, respectively, for the depth of 0 to 0.45 m. Considering thefact that the adjusted b values lie within the expected range for the soil types at the sites, we believe that physically basedmodels such as CLASS have promising potential for agricultural and meteorological applications.
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Wen et al. (1998) studied this question.