Hydrologic response of a high altitude glacierized basin in the central Tibetan Plateau

Hydrologic cycles of most high altitude glacierized watersheds in the Tibetan Plateau are not closely monitored due to their inaccessibility. Understanding the hydrologic cycle in such a basin may provide insight into the role climate plays on changes in glacier mass. Thus, hydrologic simulations with a physical perspective in the Tibetan glacierized watershed are of great significance. A high altitude glacierized basin in the central Tibetan Plateau, Qugaqie basin, was investigated with an energy-balance based glacier-melt model and the Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model. With these two models, glacier mass balance was estimated and basin runoff from glaciers was simulated at a daily time step. Results from the simulation period (October 1, 2006–September 30, 2011) demonstrated that the glaciers experienced a large negative surface mass balance with the cumulative value of −300cmw.e.. In other words, up to 13.93×106m3 water volume was melting out from the glaciers during these five years. In the 2007/08year, however, the glaciers experienced a surplus mass balance because of the low air temperature and increased precipitation in the summer season. Infiltration, evapotranspiration (ET), and overland flow were also calculated using the GSSHA model. Results showed that precipitation, the main water source, contributed roughly 95% to the total mass gain of the annual water balance in the Qugaqie basin during the study period, while the glacial runoff (snow/ice melting) contributed 5% water balance. In the water loss, 17% of annual water volume was consumed by the ET process. As a result, the remaining water volume (83%) converted to the basin river flow to the Lake Nam Co. In the summertime, the glacial runoff accounted for 15% of the total basin runoff volume, while this contribution increased in the upstream portion to 46% due to a large percentage of glacierized area. The analysis showed that the glacial runoff contributions to the total river flow decrease significantly due to the decreased air temperature in the summer of 2008. In general, the integrated model produced acceptable estimations of hydrologic response in this high altitude glacierized basin, which is jointly fed by precipitation and glacial runoff. This study suggests that, a process-based model for glacierized basins can provide a reasonable simulation of hydrologic response and further enhance our understanding of this high altitude region in the Tibetan Plateau.