A SIMPLE HYDROLOGICALLY BASED MODEL OF LAND-SURFACE WATER AND ENERGY FLUXES FOR GENERAL-CIRCULATION MODELS

A generalization of the single soil layer variable infiltration capaci ty (VIC) land surface hydrological model previously implemented in the Geophysical Fluid Dynamics Laboratory general circulation model (GCM) is described. The new model is comprised of a two-layer characterizat ion of the soil column, and uses an aerodynamic representation of the latent and sensible heat fluxes at the land surface. The infiltration algorithm for the upper layer is essentially the same as for the singl e layer VIC model, while the lower layer drainage formulation is of th e form previously implemented in the Max-Planck-Institut GCM. The mode l partitions the area of interest (e.g., grid cell) into multiple land surface cover types; for each land cover type the fraction of roots i n the upper and lower zone is specified. Evapotranspiration consists o f three components: canopy evaporation, evaporation from bare soils, a nd transpiration, which is represented using a canopy and architectura l resistance formulation. Once the latent heat flux has been computed, the surface energy balance is iterated to solve for the land surface temperature at each time step. The model was tested using long-term hy drologic and climatological data for Kings Creek, Kansas to estimate a nd validate the hydrological parameters, and surface flux data from th ree First International Satellite Land Surface Climatology Project Fie ld Experiment intensive field campaigns in the summer-fall of 1987 to validate the surface energy fluxes.