## 3 Results
### Correlation between Grassland NPP and Meteorological Factors  
Meteorological factors, i.e., precipitation, temperature, and sunshine duration, are important factors affecting grassland NPP [83]. Figure 11 shows the map of the average meteorological factors in Inner Mongolia from 2000 to 2020. In order to investigate the main climatic driving factors for grassland NPP in Inner Mongolia during 2000-2020, the spatial distribution of the correlation coefficients and partial correlation coefficients was considered in this study. As shown in Figure 12a,b, a positive correlation between grassland NPP and precipitation is seen in 97.06% of the total area. When removing the influence of the other meteorological factors, about 98.58% of the total shows a positive relationship. Thus, pre \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & & \multicolumn{2}{c}{**2000-2010**} & \multicolumn{3}{c}{**2010-2020**} & \multicolumn{3}{c}{**2000-2020**} \\ \cline{2-10}  & **Area** & **Total NPP** & **Average NPP** & **Area** & **Total NPP** & **Average NPP** & **Area** & **Total NPP** & **Average NPP** \\  & **(km\({}^{2}\))** & **(Tg C)** & **(g C/m\({}^{2}\))** & **(km\({}^{2}\))** & **(Tg C)** & **(g C/m\({}^{2}\))** & **(km\({}^{2}\))** & **(Tg C)** & **(g C/m\({}^{2}\))** \\ \hline Total area of lost & 24,016.81 & 8.29 & 345.23 & 48,920.19 & 14.96 & 305.79 & 59,141.81 & 17.63 & 298.16 \\ grassland & 5173.50 & 1.77 & 342.51 & 26,495.25 & 8.36 & 315.49 & 26,130.44 & 7.41 & 283.39 \\ grassland to bare land & 3288.31 & 0.35 & 105.47 & 8805.19 & 0.89 & 100.72 & 9550.56 & 0.97 & 101.87 \\ Grassland to forest & 8753.63 & 5.06 & 578.19 & 7067.31 & 4.18 & 590.83 & 12,131.13 & 7.04 & 580.32 \\ Grassland to others & 6801.38 & 1.11 & 163.41 & 6552.44 & 1.54 & 234.71 & 11,329.69 & 2.22 & 195.58 \\ Total area of new & 38,304.13 & 9.65 & 251.91 & 39,361.56 & 10.73 & 272.55 & 63,870.50 & 16.38 & 256.40 \\ cultivated land to grassland & 9813.00 & 3.24 & 330.65 & 10,865.88 & 4.49 & 412.76 & 14,918.88 & 6.02 & 403.38 \\ Rare land to grassland & 15,733.63 & 0.74 & 46.94 & 19,679.31 & 1.62 & 82.48 & 33,086.56 & 2.32 & 69.97 \\ Forest to grassland & 8964.25 & 4.96 & 553.08 & 6410.50 & 3.89 & 606.86 & 111,63.56 & 6.94 & 597.87 \\ Others to grassland & 3793.25 & 0.71 & 186.70 & 2411.38 & 0.73 & 304.05 & 4251.50 & 1.10 & 258.75 \\ \hline \end{tabular}
\end{table} 
Table 6: Changes of grassland NPP in Inner Mongolia based on the different land-use changes during 2000-2010, 2010–2020, and 2000-2020. Figure 11: Map of (**a**) the total annual precipitation, (**b**) average annual temperature, (**c**) total annual sunshine hours in Inner Mongolia from 2000 to 2020.  
cipitation is the main factor affecting grassland growth in Inner Mongolia. According to the statistics, 70.59% of the grassland area has a higher partial correlation coefficient than correlation coefficient, which indicates that there is a lack of precipitation in most areas of the Inner Mongolia grassland. Thus, an increase in precipitation can greatly promote the growth of the grassland and increase the NPP. The areas with high partial correlation coefficients are distributed in east Ordos, north Xilingol, and west Hulun Buir. The correlation in the south side of the Greater Khingan Range is lower than that in the north side. However, the precipitation is generally sufficient in the south side, and when the precipitation is sufficient, the grassland NPP can be affected by the other meteorological factors, and the effect of precipitation is weakened. For temperature, the correlation between NPP and temperature is not consistent in spatial distribution, as shown in Figure 12c,d. About 61.80% of the total grassland area  
Figure 12: Spatial distribution of the correlation coefficients and partial correlation coefficients between grassland NPP and precipitation (**a,b**), temperature (**c,d**), and sunshine duration (**e.f**) in Inner Mongolia during 2000–2020.