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

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 ~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 (R2 = 0.94; RMSE = 0.21 mm d−1; bias μ = 0.11 mm d−1), whereas FAO-56 consistently underestimated ET (R2 = 0.88; RMSE = 0.82 mm d−1). Under water-limited conditions, model correspondence remained strong but attenuated (ETMETRIC–ETAQUACROP: R2 = 0.75; RMSE = 0.64 mm d−1; ETMETRIC–ETFAO-56: R2 = 0.95; RMSE = 0.59 mm d−1), with METRIC exhibiting a persistent positive bias (μ = 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.