Calibration and validation of three evapotranspiration models in a tea field in the humid region of south‐east China

Abstract Evapotranspiration (ET c ) is the most important part of agricultural water consumption. Accurate determination of the ET c of tea trees is important in the water management of tea fields. In this study, three models, the Penman–Monteith (PM), Priestley–Taylor (PT) and crop coefficient (KC) models, were applied and calibrated using meteorological data of 2017 in a tea field. The calibrated models were validated using the Bowen ratio energy balance (BREB) method with the data of 2018 and 2019 in the tea field. The canopy resistance of the PM model was calibrated by the inverse method with the BREB‐measured ET c using the Katerji and Perrier (KP) submodel with R 2 equal to 0.80. The annual mean value of the coefficient in the PT model ( α = 1.03) was determined based on the BREB results and meteorological data. In addition, the crop coefficients of tea trees based on the measured ET c and reference evapotranspiration (ET 0 ) were comprehensively evaluated, with values of 0.86, 1.19 and 0.96 at the three growth stages, showing a cyclical evolution within a year. The PT model performed best, with a root mean square error (RMSE) equal to 0.82 mm day −1 and a Nash–Sutcliffe efficiency (NSE) equal to 0.90. The PM model underestimated ET c with RMSE equal to 0.79 mm day −1 and NSE equal to 0.84, while the KC method overestimated ET c .