## 5 Results  
### Data Fusion  
To assess the accuracy of six TWSC results, we plotted the spatial distribution maps of uncertainties of TWSC results from six GRACE solutions in the ARB (Figure 3). We found that the uncertainties of TWSC results from the four SH solutions are smaller than the ones from the two Mason solutions. As all the TWSC results from four SH solutions show the uncertainties are greater than 17 cm, while the TWSC results from two Mason solutions exhibit uncertainties are between 17 cm and 25 cm in the part of ARB. In particular, the uncertainties of TWSC results from JPL-SH are higher than 16 cm in the part of ARB relative to the other three GRACE SH solutions. The red region of Figure 3(f) (JPL-M) is larger than that of Figure 3(e) (CSR-M), it explains that the uncertainties of TWSC results from JPL-M are higher than those from CSR-M. Overall, all the TWSC results reveal a similar spatial distribution of uncertainties, that is, the western and southern of ARB show that the uncertainties are smaller and the larger uncertainties are mainly concentrated in the northeast of ARB. To evaluate the uncertainties of TWSC results from six GRACE solutions, we used the median of all uncertainties gridded values to measure the total uncertainty in the study region (Table 3). From Table 3, we sorted by the uncertainty in ascending order, the arrangement of GRACE solutions is CSR-SH (43.153 mm), ITSG-SH (43.315 mm), GFZ-SH  
Figure 3: The spatial distribution of uncertainties of TWSC results from six GRACE solutions. (43.628 mm), JPL-SH (44.594 mm), CSR-M (10.900 mm) and JPL-M (116.491 mm). It suggests that two Mason solutions have the greater uncertainties than four SH solutions, and the accuracy level of four SH solutions are not much different. To improve the accuracy of TWSC results from GRACE solutions, we fused six TWSC results from GRACE solutions by the least square method. We plotted the spatial distribution map of uncertainties of fused results (Figure 4). The uncertainties of fused results in the most region of ARB are less than 4 cm, while those in the northeast ARB are greater than 4 cm and the maximum value reaches 12 cm. Comparing Figures 3 and 4, the uncertainties of fused results are significantly smaller than those of any single GRACE solutions. Table 3 shows that the uncertainties of TWSC results from six GRACE solutions are greater than those of fusion results (36.577 mm). We compared the time series of TWSC results from six GRACE solutions and fused result in the ARB during 2003 and 2020 (Figure 5) and calculated the correlation coefficients between fused result and six GRACE TWSC results (Table 4). Figure 5 shows that the change trends of seven time series of TWSC results are basically the same and they all have significant seasonal variation. The TWSC results from two Mason solutions have the greater magnitudes than those from four SH solutions and fused result, and the magnitudes of fused result and the TWSC results from SH solutions are very close. It is related to the uncertainty results of TWSC results from six GRACE solutions. As the uncertainties of TWSC results from SH solutions are smaller than those of Mason solutions, the weights of SH solutions are larger than those of Mason solutions. From Table 4, the fused result has the strongest correlation with CSR-SH (0.9962), followed by JPL-SH (0.9957), GFZ-SH (0.9955), ITSG-SH (0.9950), CSR-M (0.8610) and JPL-M (0.8363). It suggests that the fused result has good consistency with TWSC results from six GRACE solutions. For convenience, we referred to the fused result as GRACE result in the subsequent study. We found that there is an 11-month data gap in these seven TWSC results. Therefore, we used Swarm data to fill this gap in a follow-up study. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**GRACE Solution** & **CSR-SH** & **GFZ-SH** & **JPL-SH** & **ITSG-SH** & **CSR-M** & **JPL-M** & **Fused Result** \\ \hline Medium (mm) & 43.153 & 43.628 & 44.594 & 43.315 & 107.900 & 116.491 & 36.577 \\ \hline \end{tabular}
\end{table}