Spillover effects of green infrastructure on the supply–demand utility of flood regulation services: A telecoupling perspective

Flood regulation services (FRS) are directional ecosystem services, for which green infrastructure (GI) provides a key biophysical foundation. However, current FRS research remains largely confined to local scales, overlooking remote upstream–downstream influences. This study constructed a novel indicator system integrating quantitative supply–demand indicators with Supply–Demand Utility (SDU). Furthermore, the Spatial Durbin Model was employed to quantify the spillover effects of GI on downstream SDU. Results indicated that Total Demand, Actual Supply, and Unsatisfied Demand accurately captured quantitative supply–demand relationships under realistic hydrological processes. SDU integrated both the physical supply–demand deficit (Unsatisfied Demand) and flood impact severity (Flood Hazard Intensity). Specifically, differences in Unsatisfied Demand among the representative flood events reflected the combined effects of flood magnitude and duration, whereas Flood Hazard Intensity generally increased with flood magnitude. Notably, the spillover effects of several GI composition variables reversed in direction across the representative events of different flood magnitudes. During the minor flood, evergreen forests and water bodies significantly reduced downstream flood hazards, whereas wetlands and grasslands exhibited opposing effects. During the major flood, evergreen forests, deciduous forests, and water bodies exhibited positive spillover effects, whereas wetlands and grasslands exhibited negative spillover effects in the baseline model. Furthermore, greater GI patch intermixing was robustly associated with reduced downstream flood hazard during the minor flood, whereas greater GI patch diversity consistently increased downstream flood hazard across model specifications during the major flood. Drawing on telecoupling theory, this study bridges the water balance principle with supply–demand indicators, providing a scientific basis for trans-regional adaptive flood management.