Evaluation of soil-vegetation interaction effects on water fluxes revealed by the proxy of model parameter combinations

The coupled development of soil and vegetation leads to a close interaction between their attributes and impacts the sustainability of eco-hydrology at different scales. In this study, a distributed hydrological model of a watershed was created with the Soil and Water Assessment Tool (SWAT) in a representative tributary watershed for investigating such effects. The results quantify the intensity and interval of the relationship and the impacts on hydrological composition between major model parameters. Among the examined interactions, SCS runoff curve number (CN2) and soil bulk density (BD) show the strongest interaction and effects on surface runoff, lateral flow, percolation, groundwater flow, and soil water content. The interaction between CN2 and BD highlights the importance of the soil surface and topsoil for runoff generation processes. In addition, the soil-vegetation interactions show clear seasonal effects due to impacts from the changes in land use and precipitation patterns, which influence the river discharge and flow variability more significantly at the sub-basin scale than at the watershed scale. The insight into the interactions and hydrological effects of soil and vegetation may help improve the spatial planning for ecological sustainability and hydrological extrema mitigation with a more reliable reflection of the spatial heterogeneity.