Comparative Analysis of Evapotranspiration from METRIC (Landsat 8/9), AquaCrop, and FAO-56 in a Hyper-Arid Olive Orchard, Southern Peru

Abstract

[EN] Accurate estimation of evapotranspiration (ET) is critical for precision irrigation in hyper-arid perennial systems. This study quantified ET in an 8 ha olive orchard in La Yarada-Los Palos (Tacna, Peru) by integrating the METRIC satellite-based energy-balance model (Landsat 8/9, Google Earth Engine) with the process-based AquaCrop model, using ETFAO-56 as an empirical benchmark. Sixteen cloud-free Landsat scenes from two contrasting seasons-2021-2022 (high-yield) and 2023-2024 (water-limited)-were processed to derive daily ET maps and model simulations aligned with satellite overpasses. Results revealed marked intra-parcel heterogeneity and clear seasonal dynamics. METRIC detected local ET peaks of similar to 6-7 mm d(-1) in densely vegetated central blocks and orchard-mean values up to 4.25 +/- 1.76 mm d(-1). During the high-yield season, ETMETRIC and ETAQUACROP showed excellent agreement (R-2 = 0.94; RMSE = 0.21 mm d(-1); bias mu = 0.11 mm d(-1)), whereas FAO-56 consistently underestimated ET (R-2 = 0.88; RMSE = 0.82 mm d(-1)). Under water-limited conditions, model correspondence remained strong but attenuated (ETMETRIC-ETAQUACROP: R-2 = 0.75; RMSE = 0.64 mm d(-1); ETMETRIC-ETFAO-56: R-2 = 0.95; RMSE = 0.59 mm d(-1)), with METRIC exhibiting a persistent positive bias (mu = 0.43-0.56 mm d(-1)) attributable to localized soil evaporation and micro-advection. Overall, METRIC provided high-resolution spatial diagnostics of canopy stress, while AquaCrop offered daily continuity and explicit evaporation/transpiration (E/Tr) partitioning, enabling a coherent multiscale assessment of ET. The integrated framework enhances operational monitoring of water use and supports deficit-irrigation optimization in hyper-arid olive systems.