Due to the increasing water stress in arid and semi-arid regions of Iran, the need for accurate, non-destructive, and cost-effective methods to estimate vegetation water consumption has become increasingly critical. The METRIC model (Mapping Evapotranspiration at High Resolution with Internalized Calibration), as an advanced remote sensing-based approach, has recently gained significant attention for estimating actual evapotranspiration (ETa) across diverse landscapes. This study aimed to evaluate the accuracy and reliability of the METRIC model in estimating ETa in the arid region of the Chahandab Plain, Varamin, using Landsat 8 Level-2 satellite imagery in combination with in-situ meteorological observations. After performing radiometric and atmospheric corrections, surface energy balance components were derived with careful consideration of local climatic conditions and land surface characteristics. The model outputs were compared with the standard FAO Penman-Monteith model due to the unavailability of data from weighing lysimeters. The results demonstrated high accuracy and strong applicability of the METRIC model under Iranian climatic conditions. The mean coefficient of determination (R²) exceeded 0.90, while the root mean square error (RMSE) remained below 0.52 mm/day, confirming the robustness of the model and its potential for use in operational water management. Furthermore, a strong correlation between ETo and ETa emphasized the critical role of vegetation density and health in regulating the evapotranspiration process, particularly in arid environments where water availability is highly variable.