Spatiotemporal variation of soil water and response patterns to key influencing factors in plantations on the Loess Plateau

Study region The Loess Plateau, China. Study focus Large-scale afforestation on the Loess Plateau has substantially improved the regional environment but has also intensified soil water depletion, highlighting the conflict between forest water consumption and water scarcity. However, systematic analyses of the spatiotemporal dynamics of post-afforestation volumetric soil water content (SWC) remain limited, particularly regarding response transitions of key influencing factors. A comprehensive understanding of the multi-factor regulation of SWC following afforestation, including the response patterns of key influencing factors, is therefore urgently needed. We compiled and screened data from published literature on Loess Plateau plantations to construct a database of SWC (0–100 cm) and its drivers. Changes in SWC in response to mean annual precipitation (MAP), stand age, mean annual temperature (MAT), land-use conversion type, and soil properties were analyzed, emphasizing breakpoint characteristics of key influencing factors. New hydrological insights for the region The results showed that SWC in the 0–100 cm soil layer declined markedly after afforestation, with an average relative reduction of 13.49%. The relative decline generally increased with stand age but decreased with increasing MAP. MAP and stand age were the primary explanatory factors of the spatiotemporal variation in relative SWC change, with relative contributions of 20.98% and 19.71%, respectively. Moreover, the pattern of relative SWC decline with increasing stand age differed significantly among MAP zones: when MAP ≤ 600 mm, the relative change in SWC exhibited an initial sharp decrease followed by a more gradual decrease, with the stand-age breakpoint delayed from 15 years (MAP ≤ 400 mm) to 22 years (500 mm ≤ MAP ≤ 600 mm); in contrast, when MAP > 600 mm, the relative SWC decline exhibited a continuous but slight reduction without an evident statistical breakpoint. The findings of this study provide a scientific basis for the regional zoning of afforestation and integrated forest and water resources management on the Loess Plateau under the principle of afforestation based on water availability.