Evaluation of evapotranspiration for exorheic basins in China using an improved estimate of terrestrial water storage change

Evapotranspiration (ET) is a critical component of the global water cycle, but basin-scale ET is often difficult to accurately estimate. Due to the limitations of the temporal resolution of the Gravity Recovery and Climate Experiment (GRACE) satellites and coverage period, daily or monthly terrestrial water storage (TWS) changes at basin scale are hard to obtain, which limits the application of water balance in ET estimation. To surmount this limitation, we established a daily TWS anomaly reconstruction framework. Based on this framework, the reconstructed daily TWS anomalies (TWSAs) were used for the first time to estimate the basin-scale ET in nine exorheic basins of China. Furthermore, we combined four commonly used ET models and TWS change (TWSC) derived by two different TWSA interpolation methods to evaluate the uncertainty of the different methodologies using the three-cornered hat (TCH) approach. The results show that: (i) the number of negative values of ET from the two TWSA interpolation methods is close to each other. For the reconstruction method, the number of negative values is reduced by about 70% relative to interpolation methods, which significantly improves the quality of the ET estimates; and (ii) among the seven sequences involved in the TCH calculation, the two TWSA interpolation methods show the largest uncertainty, while the reconstruction method has similar or optimal performance to the four ET models in all the basins except the Huaihe River Basin and the Minjiang River Basin. The results of this study demonstrate the superiority of derived TWSC based on the reconstruction framework in basin-scale ET estimation, which has a great potential for the application in the quantitative evaluation of ET and further assessment of ET models.