Runoff component quantification and future streamflow projection in a large mountainous basin based on a multidata-constrained cryospheric–hydrological model

Abstract

The Yarlung Tsangpo River (YTR) is one of several major rivers originating on the Tibetan Plateau (TP). Large uncertainties exist in studies related to streamflow variations in this basin, and such investigations are difficult due to the widely distributed snowpack, glaciers, and permafrost, as well as their complex effects on hydrological processes. In this study, we conducted a systematic analysis of the streamflow variations and runoff components in the YTR basin, using a physically based hydrological model validated by streamflow and multiple datasets related to cryospheric processes. The main findings of this work are as follows: 1. The contributions of both snowmelt and glacier melt runoff to streamflow are limited (about 5 %–6 % for the whole basin), and these contributions might have been overestimated in previous studies. 2. Annual runoff will evidently increase in the future. The relative change in annual streamflow could exceed 90 mm (∼ 38 %) at the outlet station in the far-future period, compared with the historical period, under the high-emission scenario. 3. Adopting more observational data to calibrate the hydrological model played a critical role in reducing the uncertainty in the hydrological simulation. The biases in the snow and glacier simulation for unconstrained data led to a marked overestimation of the contributions of snowmelt and glacier melt runoff to streamflow and, further, introduced an underestimation of the increasing trends of annual runoff by approximately 5 %–10 % in the future projection. These results provide a relatively reliable reference for the streamflow change and runoff components in both the historical and future periods in the YTR basin, as more datasets were used to constrain the model uncertainty compared with previous studies.