Regional difference in runoff regimes and changes in the Yarlung Zangbo river basin

Abstract. An improved understanding of runoff regimes and flow changes in the Yarlung Zangbo (YZ) river basin in the southern Tibetan Plateau (TP) is crucial for water resources management. However, regional characteristics in runoff regimes and changes are not comprehensively investigated in the YZ mostly due to the lack of hydrometeorological observations. Here, we comprehensively investigated runoff regimes and changes across six sub-basins in the YZ for 1971–2020 with a particular focus on the comparison between the upstream of the Nuxia (NX) basin and the downstream NX-Pasighat (NX-BXK), based on a newly generated precipitation dataset and a well-validated model with streamflow, glacier mass and snow cover observations. Our results reveal that large regional differences in runoff regimes and changes exist in the YZ basin. Firstly, runoff generation is dominated by rainfall in the entire YZ, and glacier runoff plays more important role in annual total runoff (19 %) in the NX-BXK than other sub-basins. Secondly, annual runoff shows an increasing trend in the NX basin but a decreasing trend in the NX-BXK due to rain-induced runoff changes, resulting in a weak increasing trend (3.1 mm/10 yr) in the YZ basin. Thirdly, total runoff increases of 5 %–22 % in the NX but decreases of 3 %–20 % in the NX-BXK in all seasons in 1998–2020 relative to the period 1971–1997. Finally, the NX basin faces a considerably hazard from extreme flood, but the NX-BXK basin faces more severe hydrological droughts. Glacier runoff shows limited roles in mitigating water shortages caused by drought in dry seasons, but it intensifies the flood frequency and severity among the basins in wet season. Our study offers a basic framework for clarifying the runoff regimes and flow changes in the TP basins.