## 3 Results
### Analysis of Land Use Change Composition of NPP in Cold and Hot Spot Areas  
Figure 7 shows the spatial distribution information of high value (hot spot) and low value (cold spot) of NPP change trend. When \(p<0.01\), the hot spots of NPP change are  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Change Trend** & **Hurst** & **Future Trends** & **Area** & **Proportion** \\ \hline \textless{}0 & 0 \textless{} H \textless{} 0.5 & Rise & 6.65 & 0.04\% \\ \textless{}0 & 0.5 \textless{} H \textless{} 1 & Continuous decline & 59.64 & 0.36\% \\ \textless{}0 & \textless{} Table & 2102.68 & 12.83\% \\ \textgreater{}0 & 0 \textless{} H \textless{} 0.5 & Decline & 329.77 & 2.01\% \\ \textgreater{}0 & 0.5 \textless{} H \textless{} 1 & Continuous rise & 13,894.17 & 84.76\% \\ \hline \hline \end{tabular} Note: Unit of area: km\({}^{2}\).  
\end{table}
Table 4: Statistics of future change trend of vegetation NPP in Beijing.  
Figure 6: (**a**) Variation trend of vegetation NPP in Beijing from 2000 to 2020; (**b**) Future trend of vegetation NPP in Beijing.  
mainly distributed in the northwest, and the cold spots are mainly concentrated in the periphery of urban area and water area.  
Land use change is one of the important driving factors of NPP. According to the cold hot spot area of vegetation NPP in Beijing as the mask extraction range, the transfer matrix of land use change in cold spot and hot spot area was extracted, so as to understand the impact of land use change on vegetation NPP change. It can be seen from Table 5 that the main land types in the hot spot of vegetation NPP in Beijing are forest and grassland, and the area of wetland and bare area is extremely few (0.019 km\({}^{2}\) and 0.022 km\({}^{2}\) in 2020, respectively). In terms of land use change, there is little transfer. The area of forest and grassland without land transformation are 1148.492 km\({}^{2}\) and 43.427 km\({}^{2}\). The transformation of land use types in hot spots mainly occurs in the transformation from grassland to forest about 21.816 km\({}^{2}\). Although other lands are still transferred to water body and impervious surface, the change area is small which is only 6.364 km\({}^{2}\) after the transformation. The main land use types in this area are still forest land and grassland.  
Figure 7: Hot spot and cold spot of vegetation NPP in Beijing from 2000 to 2020.  
As can be seen from Table 6, the area of impervious surface without land use transformation in cold spot (_p_ < 0.01) area is 708.79 km\({}^{2}\), and the area of other land use types transformed into impervious surface is 1532.14 km\({}^{2}\) in total, leading to a low level of NPP in this region. Land use transformation in cold spot area mainly occurs between cropland to impervious surface, forest to grassland and grassland to other land use types. In 2000, 1305.30 km\({}^{2}\) cropland was converted to impervious surface in 2020, while 37.92 km\({}^{2}\) forest land, 183.51 km\({}^{2}\) grassland along with 5.26 km\({}^{2}\) water body was also turned into impervious surface. With the continuous strengthening of urban development in Beijing, the rapid expansion of construction land areas is the main reason for the cold spot areas of NPP.