# Impact of Natural and Human Factors on Dryland Vegetation in Eurasia from 2003 to 2022
###### Abstract
Additionally, an increasing amount of evidence suggests that water availability, including soil moisture (SM), atmospheric vapor pressure deficit (VPD) and terrestrial water storage (TWS), plays an increasingly crucial role in determining vegetation activity over drylands [25; 26; 27]. Among them, VPD denotes the difference between saturation vapor pressure and the actual water vapor pressure at a given temperature [28]. Vegetation experiences water stress due to both high atmospheric water demand and limited water supply during drought events, leading to diminished vegetation growth with higher VPD [28]. A recent study highlighted that VPD had a widespread constraint on the interannual variability of GPP [29]. However, the constraints of VPD variations affecting vegetation growth in the Eurasian drylands has not been quantified. Moreover, recent research suggests that dryland vegetation may be particularly sensitive to soil moisture [30] and that TWS, which quantifies total water availability, can affect vegetation more rapidly than precipitation changes alone [31; 32]. Eurasian drylands, as a region strongly regulated by water availability, are influenced by the accessibility of water, which in turn affects vegetation [6]. Therefore, variations in individual water factors alone cannot fully explain vegetation activity in drylands. In addition to various natural factors, human activities can also influence dryland vegetation at the landscape scale [33]. For instance, the conversion of farmland to forests and grassland driven by policy initiatives, such as the \"Grain for Green\" program, has increased vegetation productivity in the Loess Plateau of China since 2000 [34]. Agricultural development is vigorously pursued in countries like Turkey, China and India, contributing to greening in the Eurasian drylands [35]. Additionally, neglecting local climate factors, engaging in irrational farming practices, excessive reclamation, overgrazing and urban expansion will cause a significant decline in vegetation coverage [36]. During the Soviet era, large swaths of steppe in northern Kazakhstan were converted to cropland, some of which were abandoned after the collapse of the Soviet Union [37]. However, in comparison to natural change, less attention has been given to the impact of human activities in the Eurasian drylands. The relative contribution of various natural and human factors on dryland vegetation is still not fully understood. Therefore, the main goals of this study are to (1) quantify the spatiotemporal patterns of vegetation greenness, productivity and photosynthetic capacity from 2003 to 2022 in the Eurasian drylands; (2) determine the impact of individual natural drivers on dryland vegetation; and (3) distinguish and quantify the contributions of both natural and human factors to the inter-annual variations in dryland vegetation. We hypothesize that both natural factors and human activities significantly influence the dryland vegetation (grass-land and cropland) in Eurasia, with distinct patterns observed in the responses of these ecosystems to environmental changes over the period from 2003 to 2022. We believe that understanding the natural factors can help reduce the financial investment required for ecological restoration initiatives. The findings may support the enhancement of vegetation growth, thereby aiding in ecological conservation efforts in Eurasian regions.