GCM grid-scale evaporation from mesoscale modeling

Abstract This paper investigates the problem of aggregation of land surface properties in a large area comparable in size with a model grid box of a GCM. The study is based on 3D numerical results obtained for atmospheric situations encountered during HAPEX-MOBILHY 1986-that is, moderate plant water stress at the beginning of summer. Estimating effective surface properties describing the spatial distribution of the vegetation and the soil texture within the large area under study is proposed as a first guess for accounting for spatial variability. Despite the nonlinear dependence of surface fluxes on both vegetation and soil water content, it is found that the effective surface fluxes computed from effective parameters with a ID column model match the areal-averaged fluxes estimated from 3D mesoscale model results with a relative error less than 10%. On the other hand, fluxes computed with prescribed surface properties associated with the dominant land use of the large domain depart significantly from the...