River systems characterized by strong groundwater–surface water interaction exhibit complex hydrodynamic responses under hydroclimatic extremes. This study investigates how infiltration-dominated river reaches modulate flow persistence during drought and floodplain activation during extreme rainfall. A two-dimensional Environmental Fluid Dynamics Code (EFDC) model was implemented for a 20. 35 km reach of the Gallinas River (Mexico) using high-resolution UAV-derived bathymetry and field-based discharge measurements. The model was calibrated and independently validated prior to simulating a 25-year return period flood (peak discharge = 1231. 8 m^3 s^-1) and a drought scenario constrained by an environmental-flow threshold (4. 1 m^3 s^-1). Results reveal the emergence of hydrodynamic thresholds driven by cumulative reach-scale losses (3. 1 m^3 s^-1), producing nonlinear downstream discharge decay under low-flow conditions and requiring a minimum upstream inflow of 7. 2 m^3 s^-1 to maintain ecological continuity. Under flood forcing, inundation patterns are primarily controlled by channel geometry and longitudinal slope reduction rather than discharge magnitude alone. These findings demonstrate that infiltration-influenced rivers exhibit dual hydrodynamic controls under contrasting extremes and highlight the importance of explicitly representing cumulative exchange processes in two-dimensional modeling frameworks. The study provides transferable insights for assessing drought resilience and flood risk in permeable or groundwater-connected river systems facing increasing hydroclimatic variability.
Rodríguez-Cuevas et al. (Mon,) studied this question.