A Comparison of Continuous Soil Moisture Simulations Using Different Soil Hydraulic Parameterizations for a Site in Germany

Abstract

AbstractContinuous time series of soil water content over a period of more than 9 months for a midlatitude sandy loam soil covered by grass are calculated with the Campbell and the van Genuchten soil hydraulic functions and the Clapp–Hornberger, Cosby et al., and Rawls–Brakensiek parameter sets. The results are compared with soil water content observed at several soil depths, and the water balance components are evaluated. The Campbell soil hydraulic functions are often used by meteorologists, whereas the van Genuchten functions are widespread among hydrologists. The simulations are performed with the “VEG3D” soil–vegetation model in stand-alone mode forced by on-site meteorological observations. The soil water content and meteorological observations were obtained within the Regional Climate Project (REKLIP) at a site in the Rhine valley in southern Germany with 10-min temporal resolution. Apart from the different soil hydraulic functions and parameter sets, the effects of different lower boundary conditions and initializations on the simulations are compared in terms of statistical quantities like mean error, bias, correlation coefficient, and least squares fit. Large differences between the various combinations are found. For the situation considered in this paper, the van Genuchten–Clapp–Hornberger, the Campbell–Cosby et al., and the van Genuchten–Rawls–Brakensiek combinations give the best overall agreement with the observations.