Spatial interrelationships between flood risk and ecosystem services in the Beijing–Tianjin–Hebei region at multiple scales

Against the backdrop of global climate change and rapid urbanization, the coexistence of intensifying flood risk and ecosystem service degradation in the Beijing–Tianjin–Hebei (BTH) region has emerged as a major constraint on regional sustainable development. This study develops an integrated framework of “multi-scale assessment–association analysis–mechanism exploration,” and comprehensively applies the InVEST model, the RUSLE model, random forest algorithms, spatial autocorrelation analysis, and coupling coordination degree models to systematically investigate the complex relationships and scale effects between flood risk and key ecosystem services—namely water yield and soil conservation—in the BTH region. The results indicate that: (1) the spatial patterns of both flood risk and ecosystem services exhibit pronounced scale dependence, with high-risk areas concentrated in piedmont plains and urban built-up zones, while high ecosystem service areas are stably distributed within the Yanshan and Taihang ecological barrier regions, resulting in a clear spatial mismatch characterized by “high risk–low service”; (2) the relationship between water yield service and flood risk demonstrates a scale reversal, shifting from a weak negative correlation at the micro-scale to a significant positive correlation at meso- and macro-scales, whereas soil conservation service consistently exhibits a stable negative correlation with flood risk at meso- and macro-scales, with the strength of this relationship increasing with scale; and (3) bivariate spatial analysis identifies spatial synergy zones of “high water yield–high flood risk” and spatial trade-off zones of “high soil conservation–low flood risk,” while coupling coordination degree assessment reveals the coexistence of coordinated and maladjusted states across the region, with relatively poorer coordination between soil conservation and flood risk. From a multi-scale perspective, this study deepens the understanding of the coupling mechanisms between flood risk and ecosystem services, and provides a scientific basis for ecological restoration, resilient urban planning, and coordinated watershed governance in the Beijing–Tianjin–Hebei region.