An optimized two source energy balance model based on complementary concept and canopy conductance

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In this study, we revised a two source energy balance model (Gc-TSEB) that is based on canopy conductance and soil moisture in evapotranspiration (ET) estimation. We estimate soil evaporation (E) using the complementary concept and soil surface temperature, therefore, the revised Gc-TSEB requires no soil moisture as input. We tested Gc-TSEB at 10 flux sites under various land cover and climate conditions. The flux-calibrated Gc-TSEB performed well in ET predictions, with determinant coefficients (R2) larger than 0.9 at most of the sites. The modeled transpiration was highly correlated with the Gross Primary Production, indicating the usefulness of the model in ET partitioning. More importantly, Gc-TSEB can be calibrated against the land surface temperature (LST), which is operationally available using remote sensing technique. Overall, daily ET that was predicted by the LST-calibrated Gc-TSEB generally matched the trends of the ET measurements at most of the sites, and R2 range from 0.63 to 0.93, with a median of 0.80, at all sites. Transpiration estimation was highly consistent with the simulations from the flux-calibrated model. Moreover, in vegetated surfaces, soil evaporation was estimated reasonably well using the LST-calibrated Gc-TSEB. However, positive biases are prevalent when vegetated fraction is smaller than 0.2, especially in cold regions because of the dramatic differences in evaporation process between summer and winter. To improve model performances, calibrating Gc-TSEB model in separated periods and using prior knowledge as constraints proved to be useful.