Empirical models for reference evapotranspiration estimation in Zhalong wetland

The reference evapotranspiration(ET₀)is a crucial factor which affects water balance analysis of wetlands. By fitting the FAO56 Penman-Monteith equation,a new empirical model is established,which can evaluate the monthly ET₀ in the region of Zhalong wetland. The meteorological data used in the model come from eight weather stations around Zhalong wetland from 1961 to 2000. Several combinations of meteorological parameters,which affect the reference evapotranspiration obviously, are introduced in lots of fitting models in order to choose the fitted expressions. According to the maximum fitting correlation coefficient(R²)and the minimum root mean square error(RMSE),the nonlinear exponential model with monthly maximal temperature,minimal temperature,total precipitation and wind speed is selected. In order to understand the effectiveness of the model,three commonly used empirical models,Blaney-Criddle,Priestley-Taylor and Hargreaves,are used to compare with the new one,and the answer is positive. The applied results show that the new model improves the R² and reduces the RMSE markedly. Consequently,it can serve as a useful tool for monthly ET₀ calculations in the study site.