The regions are one of the most typical examples of water constraints on the global terrestrial ecosystem, with sparse precipitation and a fragile eco-environment. Global drylands play an important role in dominating the interannual variability in global carbon sequestration of the terrestrial ecosystem owing to their extreme sensitivity to climatic change and environmental factors [6; 10; 11]. However, vegetation greening in global drylands accelerates water losses in terrestrial ecosystems via increasing evapotranspiration and decreasing SW, further disrupting the water balance of the terrestrial ecosystem [12; 13; 14]. Investigating the dominance of water pressure to dryland ecosystems is consequently of great importance, not only to explore the response pattern of vegetation growth to enhanced atmospheric and SW deficits in global drylands in the context of global climate change and human activities but also to comprehend the potential mechanism in global carbon budget dynamics and its interannual variability. Numerous studies have examined vegetation dynamics and how they respond to climate change and anthropogenic activity using statistical techniques and Dynamic Global Vegetation Models (DGVMs) [4; 6; 15]. Globally, vegetation greening is primarily attributed to rising CO\({}_{2}\) concentrations [16; 17]. The CO\({}_{2}\) fertilization effect is responsible for the co-occurrence phenomenon between growing ecosystem greening and atmospheric drying over worldwide drylands [2], and it can appropriately regulate the stomatal behaviors of ecosystem plants to balance plant transpiration and carbon absorption on the leaf scale [18; 19]. Furthermore, precipitation and SW were found as the dominant factors for vegetation growth in global drylands [20; 21; 22], as dryland vegetation heavily relies on root water content [23; 24]. Worldwide, there is a strong correlation between vegetation resilience and water availability, with lower vegetation resilience found in areas with greater interannual fluctuations in precipitation [25; 26]. Under global warming, global precipitation showed a slightly increasing trend, positively contributing to vegetation growth in water-limited vegetated areas [27; 28]. Vegetation exhibited increasing sensitivities to precipitation in drylands [19], primarily due to the enhanced CO\({}_{2}\) fertilization effect that efficiently reduces water consumption to maximize carbon accumulation on the leaf scale by upgrading leaf-scale Water Use Efficiency (WUE) [10; 19; 29; 30]. However, vegetation change-driven water evapotranspiration in the biological process of land-atmosphere coupling, in turn, increased the variability of the water cycle in drylands [31; 32; 33]. As a result, vegetation greenness and primary productivity would be tremendously constrained by enhanced atmospheric water dryness and SW deficits in dryland ecosystems [34; 35; 36]. Concurrent processes in the interactions between significant CO\({}_{2}\) fertilization and enhanced atmospheric and SW constraints on greening drylands bring uncertainties into future predictions in the evolutionary direction of ecosystem greening in global drylands. Enhanced water constraints, i.e., increasing VPD and decreasing SW, generally induce decreases in vegetation greenness and primary productivity [19; 29; 37]. In terms of SW, a succession of literature reveals that SW is the primary driver of water stress to changes in carbon-water fluxes [38] and vegetation productivity [39], and this dominance of SW is growing in Eurasian drylands [40]. Furthermore, SW exhibits significant vertical discrepancies at varying surface depths, meaning that different depths of SW contribute differently to vegetation growth worldwide. However, little is known about the intrinsic mechanism of how SW at various soil depths contributes differently to greening drylands.