# Desertification Mitigation in Northern China Was Promoted by Climate Drivers after 2000
## 4 Discussion  
### Effects of Different Climatic Factors  
The above analysis indicates that climate drivers promoted the mitigation of desertification in NC after 2000. PNPP can reflect the influence of climate drivers on desertification. Figure 7: Different factors (human activity, climate drivers, and both) affected the mitigation and exacerbation of desertification (**top,middle top**) from 1984 to 2000 and (**middle bottom,bottom**) from 2001 to 2014. The inset figures represent the total areas of desertification mitigation and exacerbation, and the pie charts represent the contributions of each factor. Therefore, according to the PNPP algorithm, an examination was conducted to determine the key factors (among the near-surface air temperature, surface evapotranspiration, and precipitation) that dominated the mitigation of desertification in NC after 2000. A rising temperature can increase soil organic carbon turnover and diminish soil productivity [85]. In addition, an increase in the near-surface air temperature can reduce soil moisture in semi-arid regions [86] and trigger soil salinization [87], which exacerbates desertification risk [88]. From 1984 to 2014, the entire DPR in NC experienced a temperature rise (Figure S7A). Meanwhile, surface evapotranspiration increased in most areas of the DPR (Figure S7D), amplifying vegetation water requirements, particularly in irrigated regions, and exacerbating soil erosion risk [89]. Compared to the period from 1984 to 2000 (Figure S7B), the temperature increase was mitigated after 2000 in the DPR of NC (Figure S7C), which may have contributed to the mitigation of desertification. However, after 2000, an increase in surface evapotranspiration occurred in these regions (Figure S7F), likely due to human activities such as farming, over-grazing, and mining [90]. This phenomenon also provides a partial explanation for the contrasting impacts of climate drivers and human activity in these regions. In arid and semi-arid regions, water availability is essential for governing ecosystems [91]. Precipitation has emerged as a dominant factor that influences NPP in these regions [92; 93]. During the period from 1984 to 2014, precipitation significantly increased over the middle-western DPR, while it decreased over the western DPR (Figure S7G), consistent with the trends of PNPP (Figure S8). Nevertheless, compared with the precipitation trend from 1984 to 2000 (Figure S7H), precipitation increased in Otinadag, Horqin, and Hulunbuir after 2000 (Figure S7I), which favored the mitigation of desertification in these regions. To further quantify the contributions of precipitation (\(P\)), evapotranspiration (\(E\)), and the near-surface air temperature (\(T\)), a method used by [PERSON] et al. [94] was adopted. The terms \(\partial PNPP/\partial P\), \(\partial PNPP/\partial E\), and \(\partial PNPP/\partial T\) are the sensitivities of individual factors (i.e., \(P\), \(E\), and \(T\)) to changes in PNPP, and the terms \((\partial PNPP/\partial P)\)dP, \((\partial PNPP/\partial E)\)d\(E\), and \((\partial PNPP/\partial T)\)dT represent the contributions of \(P\), \(E\), and \(T\), respectively, to changes in PNPP. The details of the method can be seen in the Supplementary Materials (Method S4). As shown in Figure 8, the spatial pattern of the PNPP changes (i.e., the potential tendency for desertification) induced by the changes in precipitation (d\(P\)) (i.e., \((\partial PNPP/\partial P)\) dP) indicated a positive contribution of d\(P\) to desertification mitigation in most regions (Figure 8A) because the sensitivity of PNPP to change in \(P\) (i.e., \((PNPP/\partial P)\)) was positive in the DPR (Figure 8B), followed by the change in \(P\) (\(\Delta P\)). Moreover, it is clear that precipitation contributed more than evaporation and temperature (Figure 8D,G). Several studies have suggested that soil moisture is an important factor for vegetation in arid regions, but its impacts show large spatial variability and temporal lag [95; 96; 97].