Identifying contributions of multi- recharge sources to streamflow by using a stepwise approach based on isotopic and hydrochemical signals in a glacierized catchment over Tibetan Plateau

Streamflow in the glacierized catchments over the Tibetan Plateau receives multi-recharge sources, such as rainfall, melt water from snowpack and glacier, and groundwater. Identifying their contributions to streamflow is challenge but it is vital for understanding streamflow and its composition in response to climate change. In this study, based on high-resolution isotopic (¹⁸O) and hydrochemical (Cl^-) data in the Yangbajing (YBJ) catchment of the Tibetan Plateau in China, we found that the hydrograph in a year can be separated into five segments, each of which is constituted of two or three dominant recharge sources. Thus, we developed a stepwise EMMA (end-member mixing analysis) method to partition the hydrograph and calculate contributions of water sources to streamflow in each segment of the hydrograph. Results show that the overall contributions of deep and shallow groundwater, melt water from glacier and snowpack, and precipitation are 21.8%, 9.8%, 37.5%, 8.5% and 22.4%, respectively, in a year. Specifically, in the low flow period (January 8 - April 26), streamflow is fed by deep and shallow groundwater (75.2% and 24.8%, respectively). In the early rising period of hydrograph (April 27-June 9) when temperature begins to rise, streamflow fed by deep groundwater decreases and its contribution by snow melt water increases (52.5% and 47.5%, respectively). In the fast-rising period (June 10-June 30), streamflow fed by deep groundwater is minor (4.8%) while snow and glacier melt water becomes the dominant recharge sources to the stream water (52.8% and 42.4%, respectively). In the summer period of July 1- September 23, the streamflow is highest, and the greatest glacier melt water and rainfall contributes to 52.4% and 36% of the stream flow, respectively. In the recession period (September 24 - January 7) when temperature drops and rainfall ceases, streamflow is fed again by deep groundwater and shallow groundwater (45.7% and 54.3%, respectively).