Attribution Analysis of Water‐Sediment Nexus Changes for the Fluctuating Backwater Zone of the Three Gorges Reservoir Under Changing Environmental Conditions

ABSTRACT As one of the carbon neutralization or reduction strategies, constructing large hydroelectric dams leads to the formation of fluctuating backwater zones (FBZs). Synchronization of water and sediment under the impacts of climatic changes and human activities over FBZs is still an open question due to the diverse particularities of the zones. Taking the FBZ of the world's largest hydroelectric power station, that is, Three Gorges Reservoir (TGR), as a typical example, we attempt to address such a question in this study. Based on analyses of water‐sediment characteristics, relationships, and covariations, the Budyko hypothesis and a sediment attribution decomposition method are coupled to quantitatively examine the impacts on the synchronization. Modeling results reveal that the construction of large cascade reservoirs dominates the decrease in sediment load (e.g., 73.9% for the Jialing River basin from 1985 to 2020), and the alteration of runoff‐sediment relationships across the FBZ. The dominator (accounting for 46.01%) of increasing annual average runoffs upstream of the FBZ is a wetting climate, while that (64.14%) for decreasing ones in the Jialing River as a tributary is human activities; by contrast, human activities play dominant roles (from 72.1% to 98.1%) in the reduction of sediment loads over the FBZ. These findings provide scientific support for addressing water‐sediment‐related issues such as navigational safety, sediment deposition, and water environment over worldwide FBZs.