# Can Data Assimilation Improve Short-Term Prediction of Land Surface Variables?
## 3 Results
### Impacts of Assimilation on Land Surface Variables Prediction
#### 3.1.2 Soil Moisture  
The statistics of \(RMSD_{Analysis}\), \(RMSD_{Model}\), and \(NIC_{RMSD}\) at the Mead site from 2003 to 2005 are shown in Table 1. As is shown, 9 out of 12 experiments experience improvement in the prediction from OL to MLDAS. The maximum relative difference is up to 60.41% in scenario IV in 2003. There are three sets of experiments that appear to be a degradation of predicting performance after assimilation. The \(NIC_{RMSD}\) is negative in scenarios I and II from 2003 to 2005, indicating that SM prediction improvements are unstable with a short data assimilation period (i.e., 15 or 45 days). The \(NIC_{RMSD}\) of scenarios III and IV generally increases in all 3 years, suggesting that forecast performance is better with the extended assimilation period.  
Figure 2: Leaf area index simulation and prediction from OL and MLDAS in 2003–2005. Results of four assimilation scenarios with different assimilation periods are given. Columns represent different assimilation scenarios in each year. The blue line in each subplot represents MLDAS simulation and prediction; the orange line in each subplot represents OL simulation; the red scatters represent LAI observations; and the shaded regions are the assimilation period, which starts from 1 May and lasts for 15 days, 45 days, 75 days, and 105 days for scenarios I, II, III, and IV, respectively.  
The detailed impacts of data assimilation on SM prediction are shown in Figure 3. As is shown, Noah-MP OL tends to overestimate SM at the Mead site from 2003 to 2005. For assimilation-prediction scenarios I and II, the data assimilation performs similarly to the OL. However, with longer data assimilation periods (scenarios III and IV), data assimilation can significantly improve SM prediction compared to OL. For assimilation-prediction scenario IV (assimilation of 105 days), the prediction of SM can reach even the maximum and minimum benchmark values for the whole future month, indicating that the data assimilation significantly impacts the prediction of future SM.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Year** & \multicolumn{2}{c}{**2003**} & \multicolumn{3}{c}{**2004**} & \multicolumn{3}{c}{**2005**} \\ \hline  & \(\mathbf{RMSD_{Madd}}\) & \(\mathbf{RMSD_{Analysis}}\) & \(\mathbf{NIC_{RMSD}}\) & \(\mathbf{RMSD_{Madd}}\) & \(\mathbf{RMSD_{Analysis}}\) & \(\mathbf{NIC_{RMSD}}\) & \(\mathbf{RMSD_{Madd}}\) & \(\mathbf{RMSD_{Analysis}}\) & \(\mathbf{NIC_{RMSD}}\) \\  & **(m3/m3)** & **(m3/m3)** & **(\%)** & **(m3/m3)** & **(m3/m3)** & **(\%)** & **(m3/m3)** & **(m3/m3)** & **(\%)** \\ \hline
**Scenario I** & 0.0102 & 0.0106 & \(-\)3.87 & 0.0233 & 0.0115 & **50.51** & 0.0084 & 0.0106 & \(-\)26.50 \\ \hline
**Scenario II** & 0.0138 & 0.0136 & **1.23** & 0.0121 & 0.0136 & \(-\)12.08 & 0.0469 & 0.0402 & **14.26** \\ \hline
**Scenario III** & 0.0386 & 0.0245 & **36.35** & 0.0224 & 0.0201 & **10.10** & 0.0251 & 0.0225 & **10.15** \\ \hline
**Scenario IV** & 0.0540 & 0.0214 & **60.41** & 0.0244 & 0.0166 & **31.93** & 0.0411 & 0.0227 & **44.83** \\ \hline \hline \end{tabular}
\end{table}
Table 1: \(\mathit{NIC_{RMSD}}\) of soil moisture in different assimilation scenarios (I–IV) in 2003, 2004, and 2005. Positive \(\mathit{NIC_{RMSD}}\) numbers are marked in bold.  
Figure 3: Soil moisture simulation and prediction from OL and MLDAS in 2003–2005. Results of four assimilation scenarios with different assimilation periods are given. Columns represent different assimilation scenarios in each year. The red solid line in each subplot represents MLDAS simulation and prediction; the blue dashed line in each subplot represents OL simulation; the green hollow scatters represent SM benchmarks; the blue bars are precipitation; and the shaded regions are the assimilation period, which starts from 1 May and lasts for 15 days, 45 days, 75 days, and 105 days for scenario I, II, III, and IV, respectively.