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The knowledge of spatial and temporal distribution of water requirement provides a relationship between land use, water allocation and consumption that can lead to an appropriate management of water resources. In the present study, based on mapping of spatial and temporal water requirement distribution and applicability of METRIC Algorithm was assessed for estimating daily evapotranspiration and seasonal water requirement, as well as crop coefficient in Qazvin highland desert. For this purpose, five high resolution (30m×30m) Landsat 7 ETM+ images were used during April to November 2000, as the agricultural activity period. The latent heat flux of evapotranspiration and instantaneous evapotranspiration were obtained based on the algorithm. The instantaneous evapotranspiration was extended to a daily scale and to the whole growing season through two extrapolation procedures. The accuracy of the maps was analyzed using lysimetric of alfalfa and maps of the produced crop coefficient were evaluated by using lysimetric of alfalfa and grass. Results indicated that relative error in crop coefficient estimation was between 0.053 and 0.138. Comparison of estimated and measured evapotranspiration demonstrated an appropriate consistency between results (r=0.92 and RMSE=0.60 mm/day). The amount of evapotranspiration at the pixel of the lysimeter location was estimated 1232 mm during the studied period. The findings revealed that METRIC algorithm can be applied as an effective, practical and affordable approach in accurate estimation of actual evapotranspiration at semi-arid and arid highlands area.