Blending the Evaporation Precipitation Ratio with the Complementary
Principle Function for the Prediction of Evaporation
Abstract
One class of descriptions of landscape evaporation is based on the
principle that actual evaporation E 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 annual evaporation
precipitation ratio (E/P) on the annual aridity index - the
Schreiber-Oldekop hypothesis, also known as the Budyko framework. While
there is no general agreement in the literature on the optimal
formulation of the “maximum possible evaporation” , the functional
forms of appear to be quite insensitive to its exact nature. This
observation allows to be equated with the evaporative demand , and this
immediately leads to a blending of the annual evaporation precipitation
ratio (E/P) with the complementary evaporation principle, and the
prediction of its unknown free parameter. As this free parameter is
found to be relatively insensitive to time scale, the complementary
functions become not only calibration-free at the annual time scale, but
also applicable even at daily time scales. The results are shown to be
applicable worldwide with experimental data from 516 catchment water
balance set-ups and 152 high quality eddy covariance flux stations. The
present approach offers a practical tool for the prediction of daily
evaporation using only routine meteorological data such as air
temperature, humidity, wind speed, net radiation, and long-term average
precipitation.