Attribution of decreasing annual and autumn inflows to the Three Gorges Reservoir, Yangtze River: Climate variability, water consumption or upstream reservoir operation?

Abstract Detection and attribution of streamflow changes would be a standing point towards optimizing the management of basin-scale water resources. The Three Gorges Reservoir (TGR), the largest hydropower project worldwide, has recently experienced obvious inflow reduction, which has restricted its capability to achieve the designed electricity generation. This study considered the design period of TGR (1961–1990) as the baseline period for evaluating inflow variations during the subsequent impact period (1991–2015). Annual inflow reduced by 6%, and seasonal inflow significantly decreased by 16% in autumn, which is the main season for filling reservoir. A new stepwise procedure with the help of a water-use model, a lumped hydrological model, and a generic reservoir operation model is presented to unravel the causes of inflow reduction. Results revealed that the drier climate predominantly caused inflow decreases. Human activities have notably enhanced in recent decades, however, they have not posed significant threats to inflow deficiency. Climate variability, water consumption, and upstream reservoir operation contributed by 78%, 15%, and 7% to decrease annual inflow while they contributed by 63%, 4%, and 33% to reduce autumn inflow, respectively. The proposed procedure can quantitatively disentangle major human impacts including water consumption and reservoir regulation. Such information enriches policy makers' knowledge for framing delicacy management of regional human activities in response to changing streamflow pattern.