Modelling hydrologic processes using a biophysically based model—application of WAVES to FIFE and HAPEX-MOBILHY

A biophysically based model (WAVES) is described which predicts the dynamic interactions within the soil-vegetation-atmosphere system. The physiological control on transpiration is a canopy resistance calculated as a function of net CO 2 assimilation rate, the vapour pressure deficit and the CO 2 concentration at the leaf surface. The soil hydrology is modelled using the Richards equation and evapotranspiration is calculated using the Penman-Monteith equation. A unique feature of the model is the modification of the vapour pressure deficit below the canopy as a function of the degree of atmospheric coupling. The model was tested using the energy flux and soil moisture measurements from the First ISLSCP Field Experiment (FIFE) and Hydrologic Atmospheric Pilot Experiment and Moddlisation du Bilan Hydrique (HAPEX-MOBILHY). The simulated net radiation, evapotranspiration and soil moisture content agreed well with the observations and with previous studies of transpiration and soil evaporation. The success of the model was due to the reasonably realistic treatment of the soil and canopy processes. The utility and limitations of the model are discussed.