A biophysical process-based estimate of global land surface evaporation using satellite and ancillary data 1. Model description and comparison with observations

A biophysical process-based model is used to estimate transpiration, soil evaporation and interception over the global land surface for a 24-month period (January 1987 to December 1988). The model parameters are determined from published records, and their geographical distribution has been prescribed according to land use and land cover data. Satellite observations are used to obtain fractional vegetation cover, isothermal net and photosynthetically active radiation, air temperature and vapor pressure deficit. Precipitation and friction velocity are derived as blended products (disaggregated and assimilated data). The calculated seasonal and geographical variations of evaporation, net radiation and soil moisture are in good agreement with field observations, catchment water balance data, and atmospheric water budget analysis; explained variances being greater than 75%. Uncertainties in the estimated evaporation are about 15 and 20%, respectively, for annual and monthly values.