## 3 Results and Discussion
### Assessing the Performance of Daily ET Estimated by MPDI-Integrrated SEBS Using HJ-1 Data  
The continuous daily ET (ET\({}_{\text{d}}\)) through the whole growing season estimated by the MPDI-integrated SEBS (ET\({}_{\text{SEBS-MPDI}}\)) and the original SEBS (ET\({}_{\text{SEBS}}\)) using HJ-1 data are compared with EC measurements in Figure 7. The results exhibit a clear overestimation in the ET\({}_{\text{d}}\) produced by the original SEBS, with scatter points above the 1:1 line, and the slope for the linear regressions was 1.19. A better agreement was obtained between measured ET and ET\({}_{\text{SEBS-MPDI}}\), with scatter points around the 1:1 line, and the slope for the linear regressions was 1.01. Regarding results from the MPDI-integrated SEBS model, \(R^{2}\) was 0.89, which indicated a strong correlation between measured ET and ET\({}_{\text{SEBS-MPDI}}\)_MAE_ and lower _RMSE_ demonstrated that the modified SEBS model made a good improvement in ET\({}_{\text{d}}\) estimation for the irrigated oasis. Corresponding to Section 3.1., the modeled ET clearly was improved when the MPDI was integrated into SEBS under low soil moisture condition (SM \(\leq\) 0.30 m\({}^{3}\)/m\({}^{3}\)); the _RMSE_ and _MAE_ decreased by 0.93 mm and 0.70 mm, respectively (Table 5). When soil moisture was greater than 0.30 m\({}^{3}\)/m\({}^{3}\), the RMSEs and MAEs between ET estimated by the SEBS and that estimated by the MPDI-integrated SEBS were close. This indicated that the MPDI-integrated SEBS model slightly improved the overestimation of the SEBS model when adequate soil moisture was available. In addition, we found that the simulated ET was always overestimated compared with EC measurements since September when the field was covered by maize residue (see Figure 8a). Similar overestimation results of ET due to crop residues have been reported by [PERSON] and [PERSON] (2012) [59]. Figure 6: H obtained from the original SEBS **(a)**; H obtained from the MPDI-integrated SEBS **(b)**; MPDI **(c)**; and LAI distribution **(d)** on 4 May, 2015. Purple circles (“1”) were samples with low LAI and high MPDI; red circles (“2”) were samples with high LAI and high MPDI. Figure 7: Comparison of ET\({}_{\text{d}}\) observations with the values obtained from the original SEBS and the MPDI-integrated SEBS. Figure 9 shows the spatial distributions and frequencies of ET\({}_{\rm d}\) generated by SEBS with and without the integration of MPDI on 3 July 2015 (DOY 185). Although it rained the day before, an obvious improvement of ET\({}_{\rm d}\) estimates after integrating MPDI occurred. The difference of the spatial mean of ET\({}_{\rm d}\) estimates from the original SEBS and the MPDI-integrated SEBS reached 0.8 mm d\({}^{-1}\). The low ET values presented dry sandy land and wheat parcels while spring wheat had matured and soil moisture was low due to less irrigation. The ET for these parcels mostly declined to 1 mm. The high ET values presented at well-irrigated, densely planted maize plots and water surfaces, where the difference of ET \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**ET Estimation Under Different**} & \multicolumn{4}{c}{**Evapotranspiration (ET)**} \\ \cline{2-5}
**Soil Moisture (SM) Conditions** & \multicolumn{2}{c}{**Root Mean Square Error (RMSE) (mm)**} & \multicolumn{2}{c}{**Mean Absolute Error (MAE) (mm)**} \\ \hline SM (m\({}^{3}\)/m\({}^{3}\)) & SM \(\leq\) 0.30 & SM \(>\) 0.30 & SM \(\leq\) 0.30 & SM \(>\) 0.30 \\ SEBS & 1.25 & 0.66 & 1.05 & 0.98 \\ MPDI-integrated SEBS & 0.32 & 0.57 & 0.35 & 0.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Error evaluations of the estimated ET from the original SEBS and the MPDI-integrated SEBS at Daman and Huazhaizi stations. Figure 8: Comparison of the time series of daily ET measured by the eddy covariance (EC) system and estimated by SEBS with and without the integration of MPDI over the growth period in 2015 at Daman station (**a**) and Huazhaizi station (**b**). values given by the original SEBS and the SM-integrated SEBS was very small.