Estimation of land surface evapotranspiration using the METRIC model in Nepal

Climatic and atmospheric properties vary significantly within a small area for a topographically diverse region like Nepal. Remote sensing can be used for large-scale monitoring of atmospheric parameters in such diverse terrains. This work evaluates the Landsat-based METRIC (Mapping Evapotranspiration at High Resolution with Internalized Calibration) model for estimating Evapotranspiration (ET) in Nepal. The slope and aspect of terrain are accounted for in our implementation, making the model suitable for regions with topographical variations. The estimations obtained from the model were compared with ground-based measurements. The root-mean-square error for hourly ET (daily ET) was 0.06 mm h−1 (1.24 mm d−1), while the mean bias error was 0.03 mm h−1 (0.29 mm d−1). These results are comparable with results from other studies in the literature that have used the METRIC model for different regions of the world. Thus, this work validates the applicability of the METRIC model for ET estimation in a mountainous area like Nepal. Further, this implementation provides ET estimation at a very high resolution of 30 m compared to the best available resolution of 5 km in earlier works, without compromising on the accuracy. ET estimation with high resolution over a large region in Nepal has applications in agricultural planning and monitoring, among others.