Trends in hydrological variables in large basins in Tibetan Plateau

The Tibetan Plateau is the source area of many major rivers in Asia, including the Indus River, Ganges River, Brahmaputra River, Yangtze River and Yellow River. It plays a key role in both hydrologic cycle and climate in eastern and south-eastern Asia. Recent studies have shown that the majority of the plateau area has experienced significant warming since the mid-1950s. This paper investigates hydrological and climatic trends for six large river basins (Yalung Zangbo River, Salween River, Mekong River, Tongtianhe River, Yalongjiang River and Yellow River) in the Tibetan Plateau during 1956-2013, and determines whether the changes in streamflow in these basins are mainly driven by the variation of climatic elements (precipitation and temperature). Our results show that during the past multi-decades, the six river basins did not exhibit distinct trends in annual streamflow (p > 0.05). Yarlung Tsangpo River at Nuxia station and Yellow River at Tangnaihai station showed a slightly decreasing trend (-0.009 mm yr(-2), -0.19 mm yr(-2)) in annual streamflow while others showed a slightly increasing trend. Annual mean temperature and precipitation at all stations except for Luning showed noticeably increasing trends. The impact of global warming on streamflow is complicated. On the one hand, annual evaporation could increase under warmer and drier air conditions, which will result in decreasing streamflow. On the other hand, meltwater will increase under global warming, which will increase streamflow. Our results suggest that climate warming in the Tibetan Plateau has speeded up the water cycle, indicated by the slight increase in streamflow. Further hydrological modelling studies should be conducted to quantify future streamflow changes and their uncertainty across the Tibetan Plateau.