Comparing Simulated Jujube Evapotranspiration from P-T, Dual Kc, and S-W Models against Measurements Using a Large Weighing Lysimeter under Drip Irrigation in an Arid Area

Accurate prediction of orchard evapotranspiration (ET) can optimize orchard water management. Based on the jujube (Zizyphus jujuba), ET was continuously measured from 2016 to 2019 using a large weighing lysimeter; the actual jujube ET was compared with the ET simulated with the Priestley-Taylor (P-T), Dual Crop Coefficient (Dual Kc), and Shuttleworth-Wallace (S-W) models, to verify the accuracy of the three models. The results showed that, from 2016 to 2019, the whole growth period of jujube ET was 532-592 mm and the crop coefficient was 0.85-0.93. The basal crop coefficients of the calibrated Dual Kc model were 0.4, 1.0, and 0.5 at the initial, middle, and ending growth stages, respectively. The overall simulation error of the Dual Kc model was low, and simulations were stable during the four years of the study. However, because of rough estimation the water stress coefficient (K-s) simulation accuracy will be reduced in the case of serious water shortage. The simulation error of the S-W model was greater than the simulation error of the Dual K-c model, and the simulations were unstable and vulnerable to interannual changes. The simulation error of the traditional P-T model was large. When the parameter "alpha" solution method was improved, the simulation accuracy was significantly improved, and the P-T model's simulation accuracy was only slightly lower than that of the Dual Kc model. However, the model was easily affected by changes in net radiation and air temperature. Therefore, the Dual Kc model is recommended for estimating the ET of young jujube trees in arid areas.