Mountain groundwater systems in glacierized regions are critical to hydrological processes, yet the pathways linking glacier melt, snowmelt, and groundwater recharge remain poorly understood. In this study, we integrate a cryosphere-surface hydrology model with numerical groundwater simulations and geochemical tracers to investigate groundwater recharge and surface water-groundwater interactions in the high-altitude Langshisha basin of the Langtang Himalaya (4094–6049 m). By quantifying the contributions of glacier melt and snowmelt to groundwater recharge, we explore how changes in cryosphere elements affect the basin’s hydrological system under current and projected climatic conditions. Model evaluation, informed by in-situ weather data, field measurements, and geochemical analysis, reveals that glacier melt accounted for up to 65% of groundwater recharge during 2012–2024, largely driven by the basin’s extensive glacier cover (40%) and high elevations. Geochemical tracers and groundwater simulations highlight a combination of shallow flow paths near the glacier toe and longer, deeper flow paths originating from higher elevations, contributing to surface water-groundwater exchange along proglacial streams. As glaciers retreat, the basin faces a dual loss: both glacier melt runoff and glacier-melt-recharged groundwater will diminish, reducing contributions to both surface water and aquifers. Furthermore, the shift from snowfall to rainfall projected in the coming decades is expected to alter groundwater recharge dynamics. Reduced snowpack will curtail snowmelt infiltration, while rainfall-driven recharge may interact differently with soils and subsurface conditions. These shifts will reshape the balance of surface water-groundwater interactions, with implications for water availability downstream.