# Desertification Mitigation in Northern China Was Promoted by Climate Drivers after 2000
## 3 Results  
### Attributions of Historical Desertification in NC during the Period from 1984 to 2014  
Validation of the CASA model's feasibility in calculating NPP was first carried out by comparing it with GLASS data, which showed that the CASA model can effectively re-produce the variations in NPP across space and time in the DPR of NC (Figure S3). The spatial distribution of NPP in the DPR of NC is displayed in Figure 2. The annual mean NPP from the GLASS could reach 39.41 g C m\({}^{-2}\), and it increased from the southwest to the northeast (Figure 2A). The ANPP calculated using the CASA model exhibited a similar spatial pattern (Figure 2B). The average PNPP could reach 242.89 g C m\({}^{-2}\) yr\({}^{-1}\), with its distribution also decreasing from the northeast to the southwest (Figure 2C). In the regions of Juggar and Ala Shan, the annual mean PNPP surpassed the ANPP by wide margins, reaching 264.38 g C m\({}^{-2}\) and 258.9 g C m\({}^{-2}\), indicating that vegetation recovery in these areas had not yet reached the ecosystem's carrying capacity. Conversely, the PNPP was relatively low in Tarim and Qinghai, measuring less than 75 g C m\({}^{-2}\) yr\({}^{-1}\). In addition, the annual mean HNPP was larger than 100 g C m\({}^{-2}\) in central and eastern Inner Mongolia and Juggar, which implies that human activities greatly influenced desertification in these regions. To evaluate the changes in desertification in NC, Figure 3 shows the linear trends for NPP from 1984 to 2014. Both the NPP from the GLASS and the ANPP calculated using the CASA model exhibited increasing trends in most regions of the DPR in NC over the past three decades, demonstrating the mitigation of desertification (Figure 3A,B). Conversely, in Hulunbuir, Otindag, and Horqin, the ANPP showed significant decreases, signifying the exacerbation of desertification in these areas. For the trends in PNPP (Figure 3C), a similar pattern of linear trends was observed in the desertification mitigation regions, indicating that climate drivers were the dominant factor in mitigating desertification from 1984 to 2014. The trends in PNPP also revealed a distinct difference in vegetation responses to climate drivers between the eastern and western regions of the DPR of NC. Additionally, HNPP changes generally exhibited a similar trend pattern to those caused by climate drivers (Figure 3D); in other words, human activity played the opposite role in desertification in NC. Specifically, the negative trend for HNPP in central and eastern Inner Mongolia (Ordos, Otindag, Horqin, and Hulunbuir) and south Xinjiang (Tarim) means that human activity supported ecological restoration and desertification mitigation. In Hexi Corridor, Qinghai, and north Xinjiang (Juggar), a positive trend for HNPP indicates that human activity decreased ecological restoration and led to the exacerbation of desertification. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Desertification Trend** & \(S_{ANPP}\) & \(S_{PNPP}\) & \(S_{HNPP}\) & **Dominant Factors** \\ \hline \multirow{4}{*}{Mitigation} & \multirow{2}{*}{\(>\)0} & \(<\)0 & \(<\)0 & Human activity \\ \cline{3-5}  & & \(>\)0 & \(>\)0 & Climate drivers \\ \cline{3-5}  & & \(>\)0 & \(<\)0 & Two factors \\ \hline \multirow{4}{*}{Exacerbation} & \multirow{2}{*}{\(<\)0} & \(<\)0 & \(<\)0 & Climate drivers \\ \cline{3-5}  & & \(>\)0 & \(>\)0 & Human activity \\ \cline{3-5}  & & \(<\)0 & \(>\)0 & Two factors \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Criteria determining the impacts of climate drivers and human activity, both individually and in combination, on the mitigation and exacerbation of desertification. As indicated by the linear trend of NPP, overall, 72.74% of the DPR in NC exhibited mitigation of desertification (SANPP > 0). These areas were primarily situated in Juggar, Tarim, Qinghai, Ala Shan, Hexi Corridor, and Ordos (see inset in Figure 4A). Meanwhile, 27.26% of the area experienced an exacerbation of desertification, specifically Otinadg and Horqin (see inset in Figure 4B).