Spatial heterogeneity and drivers of surface-groundwater interactions in the Yarlung River Watershed during the peak meltwater season under climate warming

This research was conducted in the Yarlung River watershed (YRW) on the southeastern Tibetan Plateau (TP), a representative alpine cold region catchment. The focus of this study is to investigate the spatial heterogeneity of surface-groundwater (SW–GW) interactions and their driving environmental factors in this alpine basin. An integrated approach combining field investigations, physical measurements, and radon isotope (²²²Rn) tracing was employed to quantify groundwater contributions (GC)—the proportion of groundwater relative to surface runoff, and to elucidate key interaction patterns controlled by geomorphology, sediment composition, and climatic forcing. The results demonstrate significant spatial heterogeneity in SW-GW interactions along the river's main stem: (1) Groundwater discharge is limited in the upstream reaches, (2) Intensive SW-GW exchange occurs in the midstream, and (3) Discharge is subsequently reduced in the downstream. Additionally, climate warming-induced changes in permafrost and vegetation cover are exerting an increasing influence on hydrological connectivity, particularly in the middle and lower reaches. The observed hydrological patterns, with minimal anthropogenic disturbance, provide a natural baseline for understanding SW-GW interactions under evolving climatic conditions. This study underscores that combining field data with isotopic process-based modeling is crucial for identifying dominant controls on SW-GW interactions in alpine regions. The findings enhance the understanding of cryosphere-hydrosphere linkages and offer a scientific basis for water resource assessment in vulnerable alpine basins. • SW-GW exchange is highly heterogeneous, with groundwater contribution (GC) ranging from 0.4% to 43.3% • Downstream sediment fining ( D 50 from 210.5 to 142.0 μm) and gradient regulate riverbed permeability • Human impact is negligible with only ∼0.7% expansion of impervious surfaces. • Steppe-to-meadow conversion and 1.15℃/decade warming enhance connectivity. • A projected 1.1 ℃ water temperature rise by 2050 will intensify leakage via permafrost degradation.