Evaluation of Two Strategies from the Sebs Model for Estimating the Daily Terrestrial Evapotranspiration Values of the Tibetan Plateau

Abstract

The terrestrial evapotranspiration (ET) of the Qinghai‒Tibet Plateau (TP) has an essential role in regulating global atmospheric circulation. Daily ET values are is usually estimated from the Surface Energy Balance System (SEBS) model in conjunction with the evaporative fraction invariant method (SEBS-INV). However, this strategy has uncertainties. A growing number of studies use daily average factors to obtain daily-scale ecohydrological outcomes, while the use of daily average elements for daily ET estimations based on the SEBS model remains relatively unexplored. In this study, we conducted a comprehensive evaluation of the SEBS-INV strategy and the daily-scale SEBS model (SEBS-AVG) for estimating the daily ET over the TP region. Estimations of daily ET values were assessed at 6 sites across the TP region. The results indicate that the SEBS-INV yielded better daily ET values, with an average R2 of 0.5 and KGE of 0.46, while the average R2 and KGE values for the SEBS-AVG were 0.43 and 0.4, respectively. The analysis further found that the temperature difference between the atmosphere and the land surface (dT) was the most influential factor affecting the performance of both strategies. Notably, the SEBS-AVG shows more sensitivity to dT than SEBS-INV. In the case of RH>70%, the outputs of the two strategies exhibited similar performances. However, under water-limited conditions (RH<70%), the SEBS-AVG significantly overestimated the ET values. These overestimations can be attributed to the impact of model input uncertainties on the estimated roughness height for heat transfer (z0h), particularly under dry weather conditions. It is noteworthy that the SEBS-AVG better captures the ET differences across vegetation types, especially in the Hengduan Mountain region. This research provides a new direction for subsequent improvements of the SEBS model at different time scales to enhance the ability of ET simulations.

Keywords: Keywords: Evapotranspiration, Qinghai‒Tibet Plateau, Two strategies, SEBS model