Fusion of the Evaporation Precipitation Ratio with the Complementary Evaporation Function: Practical Implications

One class of descriptions of landscape evaporation is based on the principle that actual evaporation and atmospheric evaporative demand exhibit complementary behavior. A feature of some recent implementations of this approach is the need for the estimation of a free parameter, usually by calibration. In a different class of representations of landscape evaporation, several functional forms have been proposed in the past for the dependency of the mean annual evaporation precipitation ratio on the mean annual aridity index - the Schreiber-Oldekop hypothesis, also known as the Budyko framework. Fusion of the mean annual evaporation precipitation ratio with the complementary evaporation principle enables the prediction of its unknown parameter. As this free parameter is found to be relatively insensitive to time scale, the complementary functions become not only calibration-free at the mean annual time scale, but also applicable even at daily time scales. The results are shown to be applicable worldwide with experimental data from 524 catchment water balance set-ups and 156 high quality eddy covariance flux stations. The present approach offers a practical tool for the prediction of daily evaporation using only routine meteorological data without calibration.