Research on Ecological and Environmental Water Requirement Threshold for Urban Rivers Based on River Health

Urban rivers are subject to intense anthropogenic disturbances, with insufficient allocation of ecological water resources leading to impaired hydrological circulation, diminished self‐purification capacity, severe degradation of biological communities and significant functional deterioration. This study investigates a quantitative methodology for determining the ecological and environmental water requirement threshold of urban rivers based on river health assessment. Acknowledging the complex, open, dynamic, coupled and nonlinear characteristics of river ecosystems, a system dynamics‐variable fuzzy set coupled model was developed by integrating variable fuzzy set evaluation with system dynamics principles. This model establishes a response relationship between the river health index and ecological flow, enabling dynamic simulation of river health conditions under different hydrological regimes. Utilizing the unknown inflection point threshold determination method, ecological and environmental water requirement thresholds were quantified to maintain basic ecosystem stability and ensure the normal functioning of river ecosystem services. The proposed framework provides theoretical support for the scientific management of urban river systems.