Role of Forest Stand Structure in Groundwater Storage Decline in the Three-North Shelterbelt Forest Region, China

Abstract. Vegetation restoration has significantly altered terrestrial ecosystem dynamics in the Three-North Shelterbelt Forest region (TNSFR), but its impacts on groundwater storage (GWS) remain poorly quantified, particularly as forest stand structure is rarely integrated. This study integrated terrestrial water storage data, land surface model simulation results, and in-situ groundwater observations to assess the spatiotemporal GWS variations. Furthermore, combining meteorological data, forest inventory data, yearbook statistics, and Normalized Difference Vegetation Index (NDVI) data explores how climate and vegetation restoration affect GWS changes. Results show that vegetation restoration in the TNSFR has exhibited a widespread upward trend, with NDVI increasing at an average rate of 0.015 decade⁻¹ over the past two decades. Concurrently, GWS has declined significantly with a mean rate of -5.47 mm yr⁻¹, primarily concentrated in regions with substantial increases in forest coverage. In groundwater-dependent ecosystems, monocultures show higher water consumption than mixed forests, and groundwater decline in mature coniferous forests is linked to high-water-consumption spruce species. Structural equation modeling confirms vegetation restoration as the leading anthropogenic driver of GWS decline in the TNSFR. This study highlights the need for tailored ecological strategies for coordinating ecological recovery with sustainable water management in dryland areas.