## 3 Results  
### Performance Assessment Based on Eddy Covariance  
Overall, the RMSEs of all four products are less than 8 mm and 31 mm at 8-day and monthly scales, respectively (Figure 2), implying that the RMSE of each product is approximately less than 1 mm per day. Residuals between predicted ET and observed ET of the four products indicates an overall overestimation of GLASS and an underestimation of the other three products. The accuracy of MOD16 is the lowest among the four ET products, with an 8-day RMSE of 0.47 mm, 0.90 mm and 0.66 mm higher than that of PML-V2, BESS and GLASS, respectively (Figure 2(a1,b1,c1,d1). Besides, its monthly RMSE is also higher than that of PML-V2, BESS and GLASS, at around 4.66 mm, 6.33 mm and 7.72 mm (Figure 2(a2,b2,c2,d2), respectively. The poor performance of MOD16 can be further proven by the boxplot of absolute error, in which it has much higher values of statistical indicators (i.e., mean value, maximum value and minimum value) than the other three products (Figure 3). The main source of the differences between MOD16 and the other three products comes from regions with low observed ET (i.e., <20 mm at an 8-day scale and <80 mm at a monthly scale) where MOD16 has a much higher overestimation than PML-V2, GLASS and BESS. It is worth noting that the difference between MOD16 and GLASS is significant (at the level of \(\alpha\) = 0.05) both at 8-day and monthly scales. Correspondingly, they have the largest MAE discrepancy of 0.93 mm and 6.72 mm, respectively, among all the product comparisons. No significant difference is found among PML-V2, BESS and GLASS both at 8-day and monthly scales (Table 4) as the RMSE and MAE of PML-V2, BESS and GLASS are very close; correspondingly, they have the largest RMSE difference at less than 0.43 mm and 3.06 mm, respectively. This can also be reflected by the boxplot of absolute error in which the statistical distributions of these three products are approximately close (Figure 2(a1,a2)). At an 8-day scale, GLASS has the lowest MAE of 0.66 mm per day, while BESS has the lowest RMSE of 0.87 mm per day. At a monthly scale, GLASS has both the lowest MAE (17.18 mm) and RMSE (22.71 mm). The monthly MAE (19 mm) and RMSE (24.10 mm) of BESS is slightly higher than that of GLASS, respectively. The good performance of BESS and GLASS indicates a slight advantage than the other products over LMRB. Figure 2: Scatterplots of 8-day (**a1**, **b1**, **c1** and **d1** for MOD16, PML-V2, BESS and GLASS, respectively) and monthly (**a2**, **b2**, **c2** and **d2** for MOD16, PML-V2, BESS and GLASS, respectively) ET products against EC ET for all the assessing sites. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Vegetation** & \multirow{2}{*}{**Time Scales**} & **MOD16 vs.** & **MOD16 vs.** & **MOD16 vs.** & **PML-V2 vs.** & **PML-V2 vs.** & **GLASS vs.** \\
**Types** & & **PML-V2** & **GLASS** & **BESS** & **GLASS** & **BESS** & **BESS** \\ \hline \multirow{2}{*}{All sites} & 8-day & 0.112 & 0.019 * & 0.064 & 0.993 & 1.000 & 0.993 \\  & Monthly & 0.124 & 0.001 * & 0.034 * & 0.579 & 0.999 & 0.805 \\ \hline \multirow{2}{*}{EBF} & 8-day & 0.018 * & 0.934 & 0.122 & 0.205 & 0.967 & 0.665 \\  & Monthly & 0.726 & 0.553 & 0.574 & 0.346 & 0.362 & 0.975 \\ \hline \multirow{2}{*}{DBF} & 8-day & 0.714 & 0.987 & 0.307 & 0.701 & 0.165 & 0.315 \\  & Monthly & 0.788 & 0.141 & 0.243 & 0.228 & 0.367 & 0.760 \\ \hline \multirow{2}{*}{Shrub} & 8-day & 1.000 & 0.534 & 0.939 & 0.446 & 0.862 & 0.988 \\  & Monthly & 0.954 & 0.148 & 0.303 & 0.164 & 0.331 & 0.673 \\ \hline \multirow{2}{*}{Grassland} & 8-day & 0 * & 0 * & 0.935 & 0.213 & 0.002 * & 0 * \\  & Monthly & 0.031 * & 0.001 * & 0.348 & 0.407 & 0.958 & 0.239 \\ \hline \multirow{2}{*}{Cropland} & Monthly & 0.097 & 0.116 & 0.071 & 0.927 & 0.881 & 0.809 \\ \hline \multirow{2}{*}{MV} & \multirow{2}{*}{Monthly} & \multirow{2}{*}{0.207} & \multirow{2}{*}{0.004 *} & \multirow{2}{*}{0.193} & \multirow{2}{*}{0.624} & \multirow{2}{*}{1.000} & \multirow{2}{*}{0.459} \\  & & & & & & & \\ \hline \hline \end{tabular}
\end{table}