## 3 Results
### Analysis of Spatiotemporal Change Trend of GPP  
The annual GPP variation in the YRB from 2000 to 2021 exhibited an obvious trend of fluctuating changes (Figure 5). The annual-scale GPP of evergreen needle leaf forests was the highest among all typical vegetation types, with a fluctuation range of 1596.64-1854.65 g C m\({}^{-2}\) y\({}^{-1}\) and an average of 1715.90 g C m\({}^{-2}\) y\({}^{-1}\) (\(p<0.01\)); two crops a year (1432.33-1682.70 g C m\({}^{-2}\) y\({}^{-1}\), 1541.31 g C m\({}^{-2}\) y\({}^{-1}\)); deciduous broad leaf \begin{table}
\begin{tabular}{l c c} \hline \hline
**Vegetation Type** & **R\({}^{2}\)** & **RMSE (g C m\({}^{-2}\))** \\ \hline Temperate Grass & 0.82 & 48.06 \\ Alpine Meadow & 0.92 & 26.57 \\ Shrub & 0.89 & 54.18 \\ Evergreen Needle Leaf Forest & 0.87 & 58.12 \\ Deciduous Broad Leaf Forest & 0.83 & 49.19 \\ One Crop A Year & 0.87 & 66.24 \\ Two Craps A year & 0.75 & 65.56 \\ Yellow River Basin Vegetation & 0.85 & 50.92 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of average R\({}^{2}\) and RMSE values for monthly-scale GPP simulation of typical vegetation types in the YRB. Figure 4: The R\({}^{2}\) and RMSE box plots of the GPP on a monthly scale simulated by the model (the quantiles are 90, 75, 50, 25, and 10 from top to bottom). forests (1107.36-1367.24 g C m\({}^{-2}\) y\({}^{-1}\), 1267.77 g C m\({}^{-2}\) y\({}^{-1}\)); one crop a year (983.3912-1160.41 g C m\({}^{-2}\) y\({}^{-1}\), 1068.85 g C m\({}^{-2}\) y\({}^{-1}\)); shrubs (777.03-974.29 g C m\({}^{-2}\) y\({}^{-1}\), 869.34 g C m\({}^{-2}\) y\({}^{-1}\)); temperate grasses (575.12-729.48 g C m\({}^{-2}\) y\({}^{-1}\), 658.10 g C m\({}^{-2}\) y\({}^{-1}\)); alpine meadows (410.36-541.69 g C m\({}^{-2}\) y\({}^{-1}\), 471.80 g C m\({}^{-2}\) y\({}^{-1}\)); Yellow River Basin (681.61-785.51 g C m\({}^{-2}\) y\({}^{-1}\), 741.90 g C m\({}^{-2}\) y\({}^{-1}\)). The change rates of annual GPP variation for each typical vegetation type were obtained through one linear regression analysis and F significance testing: evergreen needle leaf forests (4.97 g C m\({}^{-2}\) y\({}^{-1}\), \(p<0.05\)); shrubs (4.24 g C m\({}^{-2}\) y\({}^{-1}\), \(p<0.01\)); one crop a year (1.11 g C m\({}^{-2}\) y\({}^{-1}\), \(p>0.1\)); temperate grasses (0.15 g C m\({}^{-2}\) y\({}^{-1}\), \(p>0.1\)); two crops a year (\(-1.80\) g C m\({}^{-2}\) y\({}^{-1}\), \(p>0.1\)); alpine meadows (\(-3.18\) g C m\({}^{-2}\) y\({}^{-1}\), \(p<0.01\)); deciduous broad leaf forests (\(-6.69\) g C m\({}^{-2}\) y\({}^{-1}\), \(p<0.01\)); Yellow River Basin (\(-0.19\) g C m\({}^{-2}\) y\({}^{-1}\), \(p>0.1\)). The annual average GPP in the Yellow River Basin from 2000 to 2021 showed distinct spatial variations (Figure 6). In the western region of the YRB, the annual average GPP remained consistently very low throughout the year. In other regions of the YRB, there was a different distribution pattern of the annual average GPP. The southern areas exhibited higher values compared to the northern areas, while the eastern and western areas appeared to have relatively higher GPP values compared to the central region, which showed relatively lower GPP values. Due to the fact that the main vegetation types in the southeastern part of the Yellow River Basin were crops, temperate shrubs, and deciduous broad-leaved forests, while the northwestern part was mainly temperate meadows and other land uses (Figure 1c), the vegetation productivity in the southeastern part was significantly higher. From an east-west perspective, temperate grasslands and other land uses were mainly distributed in the central part of the Yellow River Basin (Figure 1c), so the GPP in the central part was slightly lower than that in the east-west part. Through the distribution map of the annual GPP change rate from 2000 to 2021, we could find that (Figure 7a) the annual GPP in the YRB showed an overall increasing trend. The majority of the regions showed an upward trend, covering approximately 59.91% of the total area of the YRB.