Soil erosion simulation using a novel dynamic LULC SWAT model in the Qinjiang River Basin, Southern Guangxi, China

This study focuses on the Qinjiang River Basin (QJRB) in Southern Guangxi, China, the core construction area of the Pinglu Canal within the Western Land-Sea New Corridor. Intensified human activities and frequent land use/land cover (LULC) changes here make it a suitable case area for investigating runoff and soil erosion processes under drastic land surface transitions. The traditional Soil and Water Assessment Tool (SWAT) model exhibits inherent simulation limitations in regions with frequent LULC changes, owing to its reliance on static LULC and oversimplified sediment transport mechanisms. To mitigate these drawbacks, a dynamic LULC-coupled SWAT model (DL-SWAT) was developed by integrating annually updated LULC data with an enhanced sediment transport module. Steep-slope croplands are identified as dominant soil erosion hotspots, with an average annual erosion intensity of 10.74 ton/ha/yr in upstream areas, 4.4 times the basin-wide average (2.45 ton/ha/yr). Forest expansion lowers surface runoff and soil detachment, while urbanization enhances surface runoff but restricts soil erosion due to impervious surfaces, revealing the joint regulatory effects of land use and terrain on regional hydrological and erosion processes. Integrating annual dynamic LULC updates at the HRU scale effectively regulates runoff-sediment coupling processes, reducing sediment overestimation by 56.9% during low-flow periods. The proposed dynamic coupling framework offers a physically consistent and accurate modeling strategy for hydrological and soil erosion simulations. • The current human activity impact on land surface dynamics is considered. • A dynamic LULC-SWAT (DLS) is proposed to enhance the simulation performance. • The DLS outperforms the SWAT, exhibiting the lowest level of uncertainty. • The Grain-for-Green policy and urbanization processes mitigate soil erosion. • Steep-slope agricultural lands are the main source of regional soil erosion.