Assessment of the modified two-source energy balance (TSEB) model for estimating evapotranspiration and its components over an irrigated olive orchard in Morocco

Olives constitute a frequently grown crop in semi -arid areas. Therefore, accurate quantification of evapotranspiration (ET) within olive groves is crucial to enhance agricultural water productivity and promote their resilience to water scarcity and future climate scenarios. In the present work, we assessed the accuracy of 3 versions of the Two -Source -Energy -Balance (TSEB) model, the first one "TSEB-SPT" using a standard Priestley -Taylor coefficient (alpha PT) to estimate the transpiration, the second one called "TSEB-CPT" constrained by a computed alpha PT using measured ET along with the equilibrium term, and the third one "TSEB-SM" where soil moisture is used as an additional constraint to improve the soil evaporation. The 3 models were applied over an irrigated olive orchard in the Tensift basin (Morocco) during two growing periods of 2003 and 2004. The comparison with ground -based flux measurements from Eddy -Covariance tower and sap flow data revealed that the TSEB-SPT model overestimates ET with an average relative error of 87% and a percentage bias of -78% during the two growing seasons. Conversely, TSEB-SM and TSEB-CPT improved ET estimates as compared to TSEB-SPT, with mean relative errors of 31% and 24% and an average percentage bias of 0.6% and -7.4%, respectively. For ET partitioning, TSEB-SM appears to be less effective in estimating transpiration, while the simulated transpiration by TSEB-CPT fits well the actual one with a root mean square error of 0.27 mm, mainly during the summer of 2003. These results open a path for future improvements: by reviewing the calibration procedure of alpha PT, and implementing alternative formulas to compute the evaporation, the TSEB-SM could be potentially a robust tool for monitoring the seasonal variation of ET and its partitioning over a heterogeneous canopy cover.