## 3 Results
### Quantitative Discrimination of Climate-Human Effect on Vegetation NPP  
The combined effects of climate-human interactions on vegetation NPP are examined through six scenarios. These six development scenarios were defined as areas with an increase in vegetation NPP via climatic change, human activities, and combined effects, as well as areas with a decrease in vegetation NPP via climatic change, human activities, and combined effects (Tables 3 and 4; Appendix A Figure 6). From 2000 to 2010, zones with human activities that promoted an increase in vegetation NPP had the largest proportion, comprising 39.92%, which was mainly distributed in Ningxia Hui Autonomous Region, Henan Province, and the junction of Heilongjiang Province and eastern Jilin Province. Zones with a reduction in vegetation NPP caused by combined effects had the smallest area, accounting for 2.21%, which was mainly distributed at the junction of Guangdong Province, Zhejiang Province, and Anhui Province. Overall, during 2000-2010, the proportion of areas with increased vegetation NPP was greater than that of areas with decreased vegetation NPP. From 2011 to 2022, zones with climate-change-promoted increases in vegetation NPP accounted for 36.03%, being mostly concentrated in Heilongjiang Province, Yunnan Province, Gansu Province, and southern Qinghai Province. Zones with a reduction in vegetation NPP caused by combined effects had the smallest area, accounting for 1.72%. In contrast, among areas with an increase in vegetation NPP, zones with climate-change-promoted increases in vegetation NPP expanded significantly, while areas that underwent human-activity-promoted increases in vegetation NPP decreased significantly. These change areas were mainly distributed in Sichuan Province, Yunnan Province, Guizhou \begin{table}
\begin{tabular}{c c c} \hline \hline
**Relative Action Zone** & **Percentage (\%)** & **Percentage (\%)** \\  & **2000–2010** & **2011–2022** \\ \hline NPP increased (climatic change) & 23.87 & 36.03 \\ NPP increased (human activities) & 39.92 & 26.99 \\ NPP increased (combined effects) & 16.11 & 11.88 \\ NPP decreased (climatic change) & 12.89 & 9.09 \\ NPP decreased (human activities) & 5.00 & 14.29 \\ NPP decreased (combined effects) & 2.21 & 1.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The area proportion of zones affected by climate–human interactions on vegetation NPP. Province, and Heilongjiang Province. For areas with a reduction in vegetation NPP, the proportion of zones with a reduction caused by human activities increased significantly. We divided the climate-human contribution rate to the increase in vegetation NPP in the study area into five equal intervals: 0%-20%, 20%-40%, 40%-60%, 60%-80%, and 80%-100%. Firstly, 0%-20% indicates that the change in vegetation NPP (increase or decrease) was almost unaffected by human activities or climate change. Secondly, 20%-40% indicates that the change in vegetation NPP was slightly affected by human activities or climate change. Thirdly, 40%-60% indicates that the change in vegetation NPP was moderately affected by climate change or human activities. Fourthly, 60%-80% indicates that the change in vegetation NPP was strongly affected by climate change or human activities. Finally, 80%-100% indicates that the change in vegetation NPP was almost entirely affected by climate change or human activities (Appendix A Figure A7). Figure 8 shows the region wherein climate change promoted an increase in vegetation NPP in 2000-2010, which was mainly distributed in North China (Figure 8a,b). In terms of climate change, the proportion of area with contribution rates greater than 80% was the largest, comprising 67.57%, which was mainly distributed in Heilongjiang Province, western Jilin Province, Shandong Province, Hebei Province, Anhui Province, eastern Qinghai Province, and northern Shanxi Province. Zones with a contribution rate between 20% and 40% had the smallest area, accounting for only 7.84%.