Unraveling river-tide process connectivity in complex deltaic networks

The Pearl River Delta (PRD) is one of the world’s most complex deltaic systems, shaped by the dynamic interaction between river discharge and tidal forces. However, the mechanisms governing river-tide connectivity within this system remain unclear, particularly with respect to the nonlinear feedback processes and spatiotemporal lag effects. This study employs an information-theoretic framework to investigate process connectivity in the PRD, integrating relative mutual information and relative transfer entropy to quantify synchrony, causality, and directional information flow among river discharge, tides, and water levels. The results reveal that river discharge predominantly governs water level synchrony in the upper PRD, while tidal dynamics exert stronger causal effects downstream water levels. Since the 1990s, human interventions have weakened the influence of river discharge, while tidal impacts have remained relatively stable. Furthermore, water level connectivity is modulated by seasonal and tidal cycles, with discharge effects dominating during flood seasons and tidal forces prevailing during dry seasons, particularly under spring tide conditions. By integrating time-lag effects, our framework reveals delayed yet physically consistent driver-response pathways and refines the spatial structure of hydrodynamic connectivity. This work presents the first lag-aware, information-theoretic quantification of river-tide connectivity in a complex deltaic system. These insights, constituting the first lag-aware, information-theoretic quantification of river-tide connectivity in a complex delta, enhance our understanding of deltaic hydrodynamics and provide a stronger basis for hydrodynamic modeling, adaptive management, and resilience planning in deltas.