###### Abstract  
Due to the effects of global warming, the vapor pressure deficit (VPD) will inevitably and continuously rise in future, which is a fact that must be faced when discussing the sustainable development of vegetation ecosystems. Understanding the response of vegetation to changes in the atmospheric moisture state is necessary for minimizing the adverse effects of climate change. Using the leaf area index (LAI) and meteorological data in the Yellow River Basin collected over nearly 40 years, we explore the spatiotemporal variations in VPD and vegetation within the growing season and the differences in the effects of VPD on vegetation in different climatic zones. The results show the following: (1) both VPD and LAI in the Yellow River Basin show an increasing trend, in which VPD increases radially outward centered on the arid regions, while the vegetation develops favorably over almost the whole basin; (2) at the whole-basin scale, the area of VPD positively correlated with vegetation growth is greater than the area of negative correlation, and this overall trend is increasing significantly; (3) the VPD exerts heterogeneous effects on different vegetation in different climatic zones, and these heterogeneity findings suggest that the effects of VPD on vegetation are more influenced by differences among the climatic zones of the vegetation than by differences in the vegetation types themselves. Our results provide insights into the effects of atmospheric moisture on vegetation growth and provide references for the sustainable development of vegetation ecosystems and future safeguarding strategies of vegetation over large spatial scales. v 2024 16 6139 18 July 2024 1  
the root to the leaf, thus affecting the absorption of nutrients from the soil, inhibiting the growth of the root system and the aboveground parts of the vegetation, and eventually reducing the growth and biomass of the vegetation [11; 12]. In addition, air pollution, such as tropospheric ozone, is phytotoxic to plants, and together with VPD modulates stomata opening, ultimately reducing yield [10]. The global surface temperature has increased by approximately 0.2 \({}^{\circ}\)C per decade over the past 30 years, accompanied by an increase in saturation vapor pressure. However, the actual vapor pressure is affected by humidity and increases at a different rate from the temperature, causing a gradual increase in the difference between the saturation and actual vapor pressures [13]. Some studies predict an exponential increase in global VPD in the future, with a relative magnitude that far exceeds the projected changes in precipitation and soil moisture [14; 15]. The effect of a continuously increasing VPD on terrestrial vegetation growth has attracted increasing attention [16; 17; 18; 19]. The satellite-based results at large scales show that vegetation productivity responses to a high VPD could be complicated. For example, in most of the wettest parts of Amazon rainforest, vegetation photosynthesis and productivity tend to increase with rising VPD [20], and there are also some wetter areas where VPD exhibits a negative effect. In terms of crop impacts, an elevated VPD negatively affected maize yields in the United States [21]; however, the increased VPD in the drylands of Central Asia promotes cropland growth [22]. Furthermore, the increased risk of impaired vegetation biomass with decreased stomatal conductance caused by a high VPD is reflected in many arid and semi-arid regions worldwide [23; 24; 25; 26]. Therefore, the relevance of VPD to vegetation is more sensitive to the dry conditions of the climatic zone in the region where the vegetation grows. The Yellow River Basin occupies an important position in China's ecological security strategy pattern, as it spans four climatic zones, namely, arid, semi-arid, semi-humid, and humid, with various atmospheric moisture states.