Diverse spatiotemporal patterns of vapor pressure deficit and soil moisture across China

Study region: China and the different climatic zones. Study focus: Vapor pressure deficit (VPD) and soil moisture (SM) are vital for the land-atmosphere hydrological cycle and vegetation growth. Understanding the spatiotemporal variations of VPD and SM is essential for exploring vegetation dynamics and ecosystem changes. However, our current understanding of the simultaneous variations of VPD and SM within specific regions remains limited. This study utilized Empirical Orthogonal Function (EOF) methods to analyze the spatiotemporal variability of VPD, surface SM (SMsurf), and root-zone SM (SMroot), respectively. We then investigated the synchronous and asynchronous variations of VPD and SM and examined their relationships with climatic factors. New hydrologic insights for the region: From 1980-2020, VPD exhibited a significant upward trend across China and in various climate zones, indicating an increase in atmospheric dryness. However, the trends of SMsurf and SMroot showed a slight upward trend across China but divergent patterns in different climate zones. In summary, approximately 43% of China experiences a significant simultaneous increase in both VPD and SM, mainly in semi-arid and arid regions. Conversely, about 4% of China shows contrasting changes in VPD and SM, primarily in humid tropical and subtropical regions. These findings enhance our understanding of VPD and SM patterns in various climates, emphasizing the significance of soil drought in humid and semihumid regions.