Ecohydrological assessment of water conservation services in China’s Yellow River Basin using sub-basin zonal optimization and spatial continuity correction

Water conservation is acritical ecohydrological function linking land-cover patterns, soil hydraulic properties and basin-scale water regulation services. To improve the accuracy of large-basin assessments and reduce local bias, this study integrated multi-source data, including land use, soil properties, and saturated hydraulic conductivity, and developed a refined sub-basin framework coupling the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model with a quadratic interpolation function constructed based on the principle of a constant second-order difference. Using sub-basin calibration, independent computation, raster mosaicking, and spatial-continuity optimisation, the spatiotemporal dynamics of water conservation in the Yellow River Basin (YRB) from 2000 to 2023 were simulated. The results indicated high simulation accuracy: after adopting sub-basin optimal Z parameters, relative errors between simulated water yield and bulletin data were <1% for most sub-basins (except Sub-basin 3 and years with invalid Z values), with a basin-wide error below 5%.; the relative errors of sub-basin water yield simulated using the quadratic interpolation-based spatial optimisation were within ±3%. After raster mosaicking, sub-basins had relative errors below 5% between simulated water yield and bulletin data. And the mean water conservation depth in the YRB was 6.86 mm, showing marked spatial heterogeneity, with low values in the northwest and high values in the southwest, southeast, and central-eastern parts of the basin. Interannually, water conservation depth increased significantly at a rate of 0.097 mm/a (p < 0.05), in synchrony with water yield depth. This study provides a transferable framework for accurately estimating large-basin-scale water conservation capacity.