Study region: Western Nyainqentanglha Mountains, Tibetan Plateau Study focus: Rock glaciers, as distinctive debris landforms prevalent in high mountain regions, are a crucial component of the regional frozen water reservoir system. However, the up-to-date distribution and hydrological significance of rock glaciers have received comparatively less attention, primarily due to considerable challenges in inventorying. Here we focus on the automated identification of rock glaciers in the semi-aird Western Nyainqentanglha Mountains using machine learning algorithms and Sentinel data, and then perform the first systematic quantification of the water volume equivalent (WVEQ) of these rock glaciers to assess their hydrological contribution to the region. New hydrolgical insights for the region: A total of 1068 rock glaciers are mapped across the region, covering an area of approximately 140.2 km2 and spanning an elevation range from 4536 to 6000 m. For these rock glaciers, the total WVEQ is estimated to be 2.33 km3, and the regional rock glacier-to-glacier WVEQ ratio is 1:13. This first-order approximation of the WVEQ provides substantial evidence that rock glaciers serve as a critical component of the regional water supply system at decadal and longer timescales. Given the increasing climate-driven imbalance of frozen water reservoirs, our findings highlight the importance of incorporating the water storage potential of rock glaciers into predictions of water availability and sustainable development strategies in the semi-arid Western Nyainqentanglha Mountains.