Investigation of a Generalized Nonlinear Form of the Complementary Principle for Evaporation Estimation

A generalized nonlinear form of the complementary principle for evaporation estimation was tested against evaporation measurements from seven flux stations in China representing different climatic conditions and ecosystem types. The method was implemented using routine meteorological data and pan evaporation measurements. The results indicate that the generalized nonlinear form with its regular boundary conditions can accurately estimate daily evaporation; its performance was somewhat better when the atmospheric evaporative demand was determined from the Penman equation than from pan evaporation. In addition, two formulations of the generalized nonlinear form, namely, a basic formulation and a more flexible quartic formulation, were compared. The comparisons indicate that the quartic formulation is not necessary and may only be needed possibly to accommodate unusual situations. The results should further advance and facilitate the application of the generalized nonlinear form to estimate daily evaporation; since only routine meteorological data are required as input, the method should be useful to generate long time series and their trends, wherever such data are available.