# Impact of Natural and Human Factors on Dryland Vegetation in Eurasia from 2003 to 2022
## 4 Discussion
Generally, a higher VPD and lower water availability (SM and TWS) would lead to a reduction in NDVI, GPP and SIF. However, the widespread intensified MAT and VPD and decreased water availability (SM and TWS) in Eurasia resulted in increases in NDVI, GPP and SIF. Our results reported that dryland vegetation was dominated by soil moisture in Eurasia. [PERSON] et al. (2019) also described that the global drylands have become greener and more productive, albeit with an enhanced VPD. In West Siberia (WSB), the effect of MAT and VPD on vegetation greening was higher than that of SM, indicating that vegetation activity in high latitudes is highly temperature-driven. [PERSON] et al. (2019) reported that the interaction between VPD and T/SM not only reduced the enhanced vegetation productivity due to warming but also increased soil drought. While TWS comprises soil moisture, surface waters and groundwater, the deep groundwater level in the Eurasian drylands makes vegetation activity more sensitive to soil moisture than to TWS ([PERSON] et al., 2019; [PERSON] et al., 2019; [PERSON] et al., 2019). Consistent with previous research findings, this study also revealed that human activities have played a dominant role in driving changes in vegetation greening in the Eurasian drylands ([PERSON] et al., 2019). However, the contribution of human activities to vegetation greening varies across different regions. Among them, human activities have the highest contribution to East Siberia, West and Central Asia, West and Central Asia, Tibet Plateau, East Asia, and the Arabian Peninsula, possibly linked to national policies determining regional vegetation types ([PERSON] et al., 2019). For example, since the late 1970s, China has enacted 13 national initiatives aimed at restoring grassland and cropland ([PERSON] et al., 2019). [PERSON] et al. (2019) found that grassland productivity increased due to the implementation of the Grain for Green Program (GGP) in Shaanxi Province. [PERSON] et al. (2019) reported that human activities led to the grassland degradation in Inner Mongolia, but that the grassland protection policies and ecological restoration projects of the Chinese government improved actual net primary productivity in most of the region's grassland from 2001 to 2014. [PERSON] et al. (2019) noted that human activities contributed to 66% of the NDVI increase in the agro-pastoral ecotone of northern China. However, we found that human activities are also a significant factor contributing to vegetation degradation in certain regions. In many areas of Kazakhstan, vegetation greenness shows a declining trend, possibly linked to the conversion of extensive grassland in the northern part of Kazakhstan into farmland during the Soviet era, with many of these farmlands abandoned after the dissolution of the Soviet Union. Despite ecological conservation measures such as fencing and rotational grazing, the rapid increase in livestock numbers may exacerbate grazing pressure, leading to intensified vegetation degradation ([PERSON] et al., 2019). Similarly, in some areas of the Loess Plateau, vegetation restoration plans may inadvertently result in vegetation degradation due to water demand surpassing the regional water resource-carrying capacity ([PERSON] et al., 2019). Additionally, rapid population growth and fast urbanization may contribute to vegetation reduction in certain regions ([PERSON] et al., 2019). Therefore, the any ecological restoration policy that will be formulated needs to consider both natural changes and the actual geographical environment. While this study quantifies the impact of natural and human factors on vegetation activity in the Eurasian drylands, there is still a certain degree of uncertainty. For example, we analyzed the correlation between temperature, precipitation, soil moisture, atmospheric drought and terrestrial water storage with vegetation activity, without considering the impact of factors such as CO\({}_{2}\) concentration, wind speed, relative humidity and solar radiation ([PERSON] et al., 2019).