Distributed hydrological model of the Qinghai Tibet Plateau based on the hydrothermal coupling: Ⅱ: simulation of water cycle processes in the Niyang River basin considering glaciers and frozen soils

The Niyang River basin is the fourth largest tributary of the Yarlung Zangbo River. Affected by glaciers, snow, and frozen soil, the water cycle relationship is extremely complex. To further study the hydrological cycle process in the region, based on the climate and geological characteristics of the Qinghai Tibet Plateau, a distributed water cycle model (WEP-QTP) for the Qinghai Tibet Plateau, which includes a "snow soil gravel layer" continuum and "snow glacier" hydrothermal process simulation, was established by improving the WEP-COR model. Through the simulation of the flow process of the Niyang River basin from 2013 to 2016, it was found that the monthly flow Nash-Sutcliffe efficiency coefficients of the Gongbujiangda and Niqu stations reached 0.810 and 0.752, respectively; these values are significantly higher than the those (0.430 and 0.095, respectively) before the improvements were implemented. Taking 2015 as an example, the flow process simulated by the WEP-QTP model during the flood season, especially before the main flood season (frozen soil thawing period), does not show large fluctuations, and the Nash-Sutcliffe efficiency coefficient of the daily flow obtained from the simulation increased from-0.67 to 0.54 compared with WEP-COR. The model improved the regulation of the groundwater aquifer, making the flow process more stable and closer to the actual measurement, for use in the hydrological simulation of the Qinghai-Tibet Plateau.