Water Isotope framework for lake water balance monitoring and modelling in the Nam Co Basin, Tibetan Plateau

Study regionThe Nam Co, the second largest and highest saline lake in central Tibetan Plateau, China.Study focusSince the establishment of the Nam Co research station, a large number of water isotope measurements in the watershed was accumulated. There is a strong need to establish an isotope framework to benefit long-term monitoring and model development. Further discussions of the water balance of the lake and water yield of the basin are also possible under an isotope framework.New hydrological insightsA water isotope framework for the Nam Co basin, including the Local Meteoric Water Line, limiting isotopic composition of evaporation and two hypothetical evaporation trajectories, is established. We further applied the isotope mass balance model to estimate the overall isotopic composition of input water to the Nam Co, the evaporation over inputs ratios (E/I) for three consecutive years, and the water yields (Wy, depth equivalent runoff) at a basin scale. Our results clearly suggest a positive water budget (i.e., E/I < 1), providing another line of evidence that the subsurface leakage from Nam Co is likely. The discrepancy between isotope-based water yields estimations and field-based runoff observations suggest that, compared to the well-studied Nyainqentanglha Mountains and southwestern mountains, the ridge-and-valley landscape in the western highlands and northwestern hogbacks are possibly low yields area, which should draw more research attentions in future hydrological investigations.