Sensitivity study of the CAPS model land-surface scheme using the 1987 Cabauw/PILPS data set

The land-surface scheme in the Coupled Atmosphere - Plant - Soil (CAPS) model is one of many schemes that participated in the Project for Intercomparison of Land-surface Parameterization Schemes (PILPS). The CAPS model, also called the Oregon State University/Phillips Laboratory (OSU/PL) Atmospheric Boundary Layer Model, has undergone development at Oregon State University and Phillips Laboratory since 1981. This model was originally designed for a global atmospheric model, but has also been used as a stand-alone model for a variety of applications. A comprehensive data set of one year (1987) including atmospheric forcing data from Cabauw has been provided for PILPS by the Royal Netherlands Meteorological Institute (KNMI). Using the Cabauw data, a series of sensitivity simulations have been carried out for the CAPS scheme. Sensitivities of latent and sensible heat fluxes to the parameters in four categories (atmospheric forcing, boundary conditions, vegetation, and soil type) have been tested. Our results show that those fluxes are sensitive to atmospheric forcing, especially to air temperature and specific humidity in the surface layer. The most sensitive and important parameters for the CAPS scheme are the roughness lengths for momentum, and heat and moisture, and the minimum canopy (stomatal) resistance.