Using long-term water balances to parameterize surface conductances and calculate evaporation at 0.05° spatial resolution

Evaporation from the land surface, averaged over successive 8 day intervals and at 0.05 degrees (similar to 5 km) spatial resolution, was calculated using the Penman-Monteith (PM) energy balance equation, gridded meteorology, and a simple biophysical model for surface conductance. This conductance is a function of evaporation from the soil surface, leaf area index, absorbed photosynthetically active radiation, atmospheric water vapor pressure deficit, and maximum stomatal conductance (g(sx)). The novelty of this paper is the use of a "Budyko-curve" hydrometeorological model to estimate mean annual evaporation rates and hence a unique value of gsx for each grid cell across the Australian continent. First, the hydrometeorological model was calibrated using long-term water balances from 285 gauged catchments. Second, gridded meteorological data were used with the calibrated hydrometeorological model to estimate mean annual average evaporation (E) for each grid cell. Third, the value of gsx for each cell was adjusted to equate E calculated using the PM equation with E from the hydrometeorological model. This closes the annual water balance but allows the PM equation to provide a finer temporal resolution for evaporation than is possible with an annual water balance model. There was satisfactory agreement (0.49 < R(2) < 0.80) between 8 day average evaporation rates obtained using remotely sensed leaf area indices, the parameterized PM equation, and observations of actual evaporation at four Australian eddy covariance flux sites for the period 2000-2008. The evaporation product can be used for hydrological model calibration to improve runoff prediction studies in ungauged catchments.