Abstract: BackgroundHydrological connectivity is central to understanding watershed eco-hydrological processes and soil-water conservation functions. In the Fujian Tulou UNESCO World Heritage Site, large-scale expansion of terraced tea plantations and the construction of associated roads and ditches have substantially altered the natural morphology of the underlying surface, forming a complex composite hydrological system intertwining natural and artificial elements. Quantifying the impact of such anthropogenic activities on watershed hydrological connectivity is essential for enabling precise ecological regulation and management, as well as for promoting sustainable watershed development. Methods This study selected the Dadi Creek watershed in the Fujian Tulou area as a case study. The year 1999, prior to large-scale tea plantation development, was designated as the baseline state, while 2023, representing a period of intensive anthropogenic intervention and mature plantation expansion, was selected as the changed state. Utilizing UAV imagery and field-investigated data, landscape elements such as terraces and ditches were finely delineated as Hydrological Response Units (HRUs). A vector-raster hybrid discretization approach was then employed to construct the hydrological network. Graph theory metrics were applied to systematically evaluate changes in structural and functional connectivity: the Shimbel Index (Shi) was used to quantify the compactness of the network structure; the Potential Flow Index (Fi) served to identify potential hubs for material transport; and the Residual Flow Index (RF) was employed to distinguish between functional "transport-enhanced zones" and "runoff-retention zones." Furthermore, the Integral Index of Connectivity (IIC) and the delta IIC (dIIC) were calculated to assess the overall functional level of the watershed and the spatial contribution of individual nodes, respectively. Finally, a dual-threshold method was implemented to precisely identify the critical connectivity nodes that exert a decisive influence on the watershed's connectivity pattern.Results Linear engineering projects such as roads and ditches significantly altered the structural characteristics of the small watershed's confluence network: gully density increased from 1.85 km/km² to 2.90 km/km², and the hydrological network structure became more fragmented (with the proportion of high-reachability nodes decreasing by 5.92%); (2) Artificial ditches optimized local runoff pathways, enhancing the potential for local material transport (the proportion of high-Fi nodes increased by 5.13%). Meanwhile, terraced tea plantations, by modifying slope micro-topography, generated a significant runoff retention effect (the proportion of nodes with RF < 0, indicative of flow retardation, increased by 2.37%); (3) The overall watershed hydrological connectivity (IIC) decreased by 14.9%. However, the spatial pattern of node importance (dIIC) revealed that new critical connectivity zones formed at the confluences of artificial ditches and the natural drainage system, marking a spatial shift of hydrological control hubs from natural river channels toward composite artificial-natural nodes.ConclusionsThe research indicates that terraced tea plantation expansion exerts a dual effect of “local enhancement but overall reduction” on hydrological connectivity. The identified key connectivity zones can provide a basis for the precise layout and management of soil and water conservation measures. Moreover, the “hydrological network–graph theory” analytical framework established in this study can also serve as a model basis for analyzing hydrological processes in similar small watersheds subject to human activities.