River networks of deltas are complex systems, responsible for the transport of water, sediment and nutrients between land and sea. Topological complexity, dynamic complexity and flux vulnerability are three characteristics to describe the material transport within a deltaic river network, and they reflect the channel number and connectivity, flux distribution, and sensitivity of flux to external disturbances, respectively. Here, graph theory was applied to estimate the three characteristics of the Pearl River Delta (PRD) in 1977 and 2008, when the human-induced uneven riverbed downcutting occurred on a large scale. By identifying the channels through which water flows from the apex to each outlet, the eight subnetworks corresponding to the eight outlets were distinguished. Although the topological complexity changes little during this period, the dynamic complexity and vulnerability have great adjustments. The dynamic complexity greatly decreases in the subnetworks that have larger riverbed downcutting comparing to their adjacent subnetworks. We further reveal the positive relation between the decrease in dynamic complexity and human-induced riverbed downcutting under the same topological complexity. Moreover, the local vulnerabilities of channels with relatively high riverbed downcutting increase, leading to the emergence of “high vulnerability channels”. These findings suggest that the human-induced uneven riverbed downcutting is the main reason for the adjustments of dynamic complexity and vulnerability. The results obtained from this study may provide scientific guidance for the further development and utilization in the PRD and other deltaic river systems worldwide subject to intensive human intervention.

三角洲的河网是复杂的系统，负责在陆地和海洋之间运输水、沉积物和营养物质。拓扑复杂性、动态复杂性和通量脆弱性是描述三角洲河网内物质传输的三个特征，它们分别反映了河道数量和连通性、通量分布和通量对外部干扰的敏感性。在这里，图论被用来估计珠江三角洲（PRD）在1977年和2008年的三个特征，当时人为引起的不均匀河床下切发生了大规模。通过识别水从顶点流向每个出水口的通道，区分出八个出水口对应的八个子网。虽然在此期间拓扑复杂度变化不大，动态复杂性和脆弱性有很大的调整。与相邻子网相比，具有较大河床下切的子网的动态复杂性大大降低。我们进一步揭示了在相同拓扑复杂度下动态复杂度降低与人为河床下切之间的正相关关系。此外，河床下切较高的河道局部脆弱性增加，导致“高脆弱性河道”的出现。这些研究结果表明，人为引起的河床不均匀下切是动态复杂性和脆弱性调整的主要原因。