## 3 Results
### Performance Based on Inter-Comparison  
Overall, all four products do not show a uniform spatial pattern, although a consistently low ET in the north and high ET in the south can be observed (Figure 4). However, each product can well reflect the spatial differences brought by topography, climate and vegetation over the entire basin. Great spatial differences can be found in local regions. The multi-year average ET of GLASS is around 100 to 300 mm higher than that of the other three products in the Xiengkhouang Plateau and the Boloven Plateau, where evergreen broadleaf forest is the dominant land cover type. MOD16 presents the lowest multi-year average ET in the Korat Plateau, the Chuor Phnum Dangrek and the Mekong Delta Region, where the land cover is dominated by croplands. Spatial differences among the four products are more obvious in the seasonal average ET. In spring, MOD16 also presents the lowest average ET in the Korat Plateau, Chuor Phnum Dangrek and Mekong Delta Region. In the other three seasons, the largest spatial disagreement among the four products is distributed \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Time** & **Products** & **Indicators** & **All Sites** & **EBF** & **DBF** & **Shrub** & **Grassland** & **Cropland** & **MV** \\ \hline \multirow{8}{*}{8-day} & MOD16 & RMSE & 7.86 & 7.62 & 7.80 & 9.26 & 4.93 & - & - \\  & MAE & 6.19 & 6.05 & 6.44 & 7.56 & 4.10 & - & - \\ \cline{2-10}  & PML-V2 & RMSE & 7.39 & 6.61 & 7.53 & 10.09 & 3.54 & - & - \\  & MAE & 5.45 & 5.28 & 6.11 & 7.76 & 2.73 & - & - \\ \cline{2-10}  & BESS & RMSE & 6.96 & 7.02 & 6.49 & 8.74 & 4.36 & - & - \\  & MAE & 5.44 & 5.85 & 5.59 & 6.94 & 3.70 & - & - \\ \cline{2-10}  & GLASS & RMSE & 7.20 & 7.13 & 7.41 & 8.21 & 3.34 & - & - \\  & MAE & 5.26 & 5.58 & 5.79 & 6.52 & 2.39 & - & - \\ \hline \multirow{8}{*}{Monthly} & MOD16 & RMSE & 30.43 & 26.19 & 30.59 & 30.49 & 16.47 & 40.10 & 38.82 \\  & MAE & 23.90 & 20.74 & 25.49 & 23.78 & 13.36 & 31.97 & 31.00 \\ \cline{2-10}  & PML-V2 & RMSE & 25.77 & 22.01 & 25.95 & 32.37 & 10.81 & 25.55 & 27.65 \\  & MAE & 19.64 & 17.48 & 21.71 & 23.51 & 8.63 & 19.92 & 21.47 \\ \cline{2-10}  & BESS & RMSE & 24.10 & 23.70 & 21.45 & 24.34 & 12.77 & 22.35 & 28.77 \\  & MAE & 19.00 & 19.55 & 18.35 & 18.94 & 10.85 & 19.14 & 22.66 \\ \cline{2-10}  & GLASS & RMSE & 22.71 & 24.46 & 25.13 & 22.64 & 10.45 & 27.65 & 22.58 \\  & MAE & 17.18 & 18.93 & 19.59 & 16.95 & 7.13 & 22.36 & 18.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Evaluation results of ET products in diverse vegetation types. in the Xiengkhouang Plateau, Boloven Plateau and Mekong Delta region. For example, the summer ET of GLASS is around 100 to 200 mm higher than for the other three products in the Xiengkhouang Plateau and Boloven Plateau. The annual average ET ranges from 800 to 1400 mm/year across the basin, according to all four products (Figure 4(a1-a4)). The highest spatial agreement among the four products can be observed in the up reach, dominated by grasslands with an annual average ET range of 400 to 600 mm/year. The ET of all products in the Three River Source Region of the up reach is relatively low (around 100 to 200 mm) as this region belongs to the snow and polar climate zone, with a mean altitude higher than 4000 m. The spatial distribution of the ET of MOD16 and PML-V2 is well consistent in summer and winter (Figure 5), especially in the Xiengkhouang Plateau, Korat Plateau and Boloven Plateau. The spatial correlation shown in Figure 6 further indicates a great spatial difference among the four products during 2001-2015. Spatial correlations between MOD16 and BESS, between PML-V2 and GLASS, and between GLASS and BESS show great spatial discrepancies. For example, high positive spatial correlations can be observed in the Korat Plateau, while negative correlations can be found in the Mekong Delta region between PML-V2 and GLASS. Conversely, negative spatial correlations can be observed in the Korat Plateau, while positive correlations can be found in the Mekong Delta region between MOD16 and BESS.