Evapotranspiration and Water Use of an Irrigated Traditional Cherry orchards using the Eddy Covariance technique and FAO56 Dual Crop Coefficient Approach

This study aims to compare the observed evapotranspiration measured with the eddy covariance tower (ETa) and the simulated actual evapotranspiration (ETc act) using FAO 56 dual crop coefficient model. Reliable data were obtained after estimating the energy flux of latent heat for evapotranspiration measured by the tower. The FAO56 dual crop coefficient approach computes and partition the actual crop evapotranspiration (ETc act) into actual tree transpiration and soil evaporation, thus adopting the basal crop coefficient (Kcb) and the evaporation coefficient (Ke) respectively. The model was used in a drip irrigated Cherry orchard (Prunus avium, cv “Bing”) located in Stockton (California, USA) where the experimental data were collected during two crop seasons (2021-2022). The model calibration was performed by minimizing the difference between the predicted ETc act and the observed daily ETa measured with Eddy-Covariance tower during the irrigation season in 2021. The validation was performed using the independent data set of ETa of the tower measurements from 2022. The calibrated Kcb was equal to 0.50 for the initial and non-growing season stages, 0.70 for the mid-season, and 0.45 for the end season. For both seasons, the goodness-of-fit indicators relative to comparing ETa observed with the simulated ETc act resulted in root mean square errors (RMSE) lower than 1 mm d−1 and a slope of the linear regression close to 1.0 (0.94 ≤ b0 ≤ 1.00). The fraction of the ground cover was 40 % and the standard deviation of the canopy is 0.75. The water balance of cherry orchards, simulated with FAO56 results in a ratio between soil evaporation (Es) and ETc act that averaged 0.31. During the mid-season, the ratio between ETc act and observed ETa measured by the eddy covariance tower varied from 0.74 to about 0.98, proving that the values of ETc act are close to the measured ETa. Preliminary results confirm the performance of the FAO 56 model using the FAO56 dual Kc approach for deciduous crops and tree crops in general, enabling farmers to estimate the crop water requirements of cherry orchards for better irrigation management.