Groundwater sustainability strongly depends on processes in the unsaturated (vadose) zone, which control infiltration, storage, and the timing and quality of recharge. Despite advances from theoretical and experimental studies, significant gaps remain in understanding and quantifying vadose‑zone processes. This session invites contributions that advance knowledge of unsaturated zone dynamics and their implications for groundwater resources under changing climates, land use, and ecosystems. We welcome observational, experimental, and modeling studies of flow and contaminant transport across scales, including soil–plant–atmosphere interactions, preferential flow, fracture and karst systems, groundwater contamination, and responses to extreme events such as droughts and intense precipitation. Integrative studies combining field observations (e.g., soil moisture, tracers, geophysics), remote sensing, laboratory experiments, and numerical or data‑driven modeling are especially encouraged. The session aims to foster interdisciplinary dialogue to improve vadose‑zone representation in groundwater assessments and support sustainable water‑resources management across diverse hydrogeologic settings.