On the Choice of Soil Hydraulic Models in Land-Surface Schemes

The uncertainties in soil hydraulic functions and soil hydraulic parameters affect the performance of land-surface schemes used in climate and weather prediction models. The Clapp–Hornberger soil hydraulic model of is most widely used in land-surface modelling, while other models favoured by soil physicists are hardly used for the purpose. In this study, we give a summary of four soil hydraulic models and examine the impact of these models on the performance of a land-surface scheme. It is found that inconsistency in soil hydraulic functions and parameters leads to different outcomes in land-surface modelling. We introduce a technique to match the soil hydraulic parameters for different models, so that the disagreement in the description of soil hydraulic properties among different models is reduced, while intrinsic differences in the soil hydraulic functions remain. The numerical tests also show that the land-surface model has a degree of tolerance to the uncertainties in soil hydraulic models, at least in the case of off-line simulations. The van Genuchten model performs well, but is numerically expensive. The Brooks–Corey and Clapp–Hornberger models are sufficiently accurate with numerical efficiency, and are therefore more suitable for land-surface schemes used in atmospheric models.