Estimating evapotranspiration using METRIC model and Landsat data for better understandings of regional hydrology in the western Urmia Lake Basin

Abstract

This study estimates the evapotranspiration (ET) from the western part of Urmia Lake Basin, Iran, to provide quality spatio-temporal evapotranspiration information for use in achieving regional sustainable water management. A “mapping evapotranspiration with internalized calibration” (METRIC) ET estimation model was adopted to estimate monthly ET for the period between 2014–2016 using Landsat 8 satellite imagery. Several refinements are made to adjust the model to the local environment. The refinements include estimating evaporation from the saline lake, correction of the underestimation of city surface temperature through the modification of thermal emissivity, as well as modifications of minor assumptions applied in METRIC. The estimation results for ET obtained using METRIC were compared with independent estimation of ET using the FAO-56 approach in order to assess the estimation accuracy. The comparison showed good correlation between the two types of estimation results for irrigated agriculture, implying successful estimation of ET in this region. ET estimated in non-irrigated bare soil fields was prone to overestimation. The novelty of this study lies in the fact that this is the first ET data for this basin with 100 m spatio-temporal resolution and accuracy information. Therefore, the estimation procedure and results are expected to contribute to a better understanding of the regional hydrology. This is necessary both for the restoration of Urmia Lake and for achieving sustainable water management in the region.