Estimation of Crop Evapotranspiration in North of Shanxi Province

Abstract

Seven representative empirical potential evapotranspiration equations selected form the radiationbased and temperature-based methods, they were evaluated and compared with the Penman-Montieth equation using daily meteorological data form Mizhi station in north of Shanxi. The comparison was first made using original constant values involved in each empirical equation and then using the recalibrated constant values, the study showed that: the original constant values involved in each empirical equation performed badly except the equation of modified Makkink and Hargreaves, the mean error was larger than 15%; Improvement was achieved for each empirical equation though the parameter recalibration by genetic algorithm, good correlation was found between the ET0 values estimated by each empirical equation and the Penman-Montieth equation, the performance of radiationbased methods was better than temperature-based in accuracy and correlation, obviously. The Gaoqiao equation was recommended to calculate the ET0 for the study region in the temperature-based methods, its mean error was less than 10%. Estimated by Prestley-Taylor and modified Makkink equation were in closest agreement with PM reference crop evapotranspiration, the mean error was less than 3%, which equation was chosen depending on the meteorological data or measured data