Study on the consistency of evaluation methods for river network connectivity in data-scarce watersheds

Hydrological connectivity, the capacity of a river network to transport water and associated materials, can be evaluated through structural and functional approaches. Structural connectivity, often assessed using readily available topographic and network data, describes the static arrangement of the river network. Functional connectivity, however, reflects the dynamic flow processes within the network, typically measured through flow data which may be scarce. While numerous structural indicators exist, their ability to represent actual (functional) connectivity remains uncertain.There is still no clear method for accurately evaluating connectivity. Functional connectivity index (FCI) provides a realistic and dynamic representation of connectivity. This study established a research framework that evaluates the consistency between structural connectivity and functional connectivity (considering FCI as actual connectivity). The research framework uses topography and graph model to calculate structural indicators and employs intraclass correlation coefficient (ICC) to evaluate the consistency. Taking the Haihe River basin as an example, the study analyzes the ability of structural indicators to characterize actual connectivity, and proposes new indicator. The results show that Betweenness Centrality (BC) has the highest consistency with FCI, with an ICC of 0.32, while other structural indicators are relatively weak. In multiple scenarios, BC defined by the network and Topographic Connectivity Index (TCI) defined by topography have the potential to characterize connectivity, and there are significant spatial differences between them. The combined index BC&TCI, which considers both network and topography, can better characterize connectivity, with an ICC of 0.40 and reaching an ICC of 0.55 in mountain area. The research framework also reveals the non-consistency between structural connectivity and functional connectivity. And the non-consistency between them can serve as a measure of river network renovation and reconstruction to avoid ecological problems caused by an imbalanced structure and function.