Surface energy balance and actual evapotranspiration of the transboundary Indus Basin estimated from satellite measurements and the ETLook model

estimated as being 112 Wm � 2 . The basin average sensible, latent and soil heat fluxes were estimated to be 80, 32, and 0 Wm � 2 , respectively. The average evapotranspiration (ET) and evaporative fraction were 1.2 mm d � 1 and 0.28, respectively. The basin wide ET was 496 6 16.8 km 3 yr � 1 . Monte Carlo analysis have indicated 3.4% error at 95% confidence interval for a dominant land use class. Results compared well with previously conducted soil moisture, lysimeter and Bowen ratio measurements at field scale (R 2 ¼ 0.70; RMSE ¼ 0.45 mm d � 1 ; RE ¼ –11.5% for annual ET). ET results were also compared against earlier remote sensing and modeling studies for various regions and provinces in Pakistan (R 2 ¼ 0.76; RMSE ¼ 0.29 mmd � 1 ;R E¼ 6.5% for annual ET). The water balance for all irrigated areas together as one total system in Pakistan and India (26.02 million ha) show a total ET value that is congruent with the ET value from the ETLook surface energy balance computations. An unpublished validation of the same ETLook model for 23 jurisdictional areas covering the entire Australian continent showed satisfactory results given the quality of the watershed data and the diverging physiographic and climatic conditions (R 2 ¼ 0.70; RMSE ¼ 0.31 mmd � 1 ;R E¼ –2.8% for annual ET). Eight day values of latent heat fluxes in Heibei (China) showed a good resemblance (R 2 ¼ 0.92; RMSE ¼ 0.04 mm d � 1 ;R E¼ 9.5% for annual ET). It is concluded that ETLook is a novel model that can be operationalized further—especially after improving the preprocessing of spaceborne soil moisture data. This preprocessing includes (1) downscaling of topsoil moisture from 25 to 1 km pixels, and (2) translation of topsoil moisture into subsoil moisture values.