Role of groundwater discharge in sustaining baseflow balance in the middle reaches of the Yarlung Zangbo River

ABSTRACT The Tibetan Plateau (TP) plays a vital role in supplying water to approximately two billion individuals residing downstream, as it serves as the source of numerous significant rivers across Asia. Nevertheless, the significance of groundwater in sustaining the plateau rivers remains uncertain, hence jeopardizing the long-term water resource sustainability of Asia. Here, we assess the groundwater contribution to river flow in the middle reaches of the Yarlungzangbo River (YR), a typical TP location, and we pinpoint the vital role that plateau groundwater plays in sustaining the water balance of the river. The findings indicate that the YR mainstream has a runoff excess of approximately 36–42 × 108 m3/a, which accounts for 22.8–26.5% of the mainstream flow and is strongly correlated with groundwater discharge. The research findings also indicate that the movement of groundwater on the plateau is primarily influenced by the variation in land elevation and replenishment at higher elevations. The contribution of groundwater is inversely proportional to the topographic steepness and precipitation, and its recharge mechanism is associated with the large-scale active fault zones in the vicinity of the YR.