Impacts of Climate Change and Land-Use Change on Hydrological Processes and Sediment Load in the Upper Cau River Basin, Northern Vietnam

Abstract

Climate change and land-use change strongly influence hydrological processes and soil erosion in tropical mountainous watersheds. This study uses the SWAT model to assess their individual and combined impacts on streamflow, sediment, and soil erosion in the Upper Cau River Basin, northern Vietnam. The model was calibrated and validated using observed hydro-meteorological data for 1997–2020 and applied to scenario-based projections of future climate (2021–2050) and land-use planning to 2050. The SWAT model demonstrated high predictive accuracy for both streamflow and sediment (NSE > 0.76, R² > 0.77). Results indicate that, relative to the baseline, the combined climate and land-use change scenario produces the largest impacts, with mean streamflow increasing by 44.95%, sediment discharge at the gauge station rising by 53.3%, and average basin-wide soil erosion reaching 12.57 t/ha/year more than a 380% increase. By comparison, climate change alone increases mean streamflow and soil erosion by 44.8% and 73.7%, respectively, while land-use change alone causes only minor changes in streamflow (+0.82%) but substantially increases soil erosion (+265%). These findings demonstrate a pronounced amplification of hydrological extremes and erosion risk when both drivers act together. Beyond scenario comparison, this study contributes a spatially explicit erosion hotspot attribution framework that links scenario forcing to hydrological response unit and sub-basin prioritisation of erosion risk. Spatial analysis reveals a basin-wide shift from predominantly low erosion under baseline conditions to widespread moderate and high erosion under the combined scenario. While the results highlight the dominant and interacting roles of climate and land-use change, they reflect SSP2-4.5 projections from a single climate model (UK Earth System Model, UKESM1-0-LL), and uncertainty across multiple climate models was not assessed. The findings provide a robust scientific basis for targeted watershed management and erosion-control planning in northern Vietnam’s mountainous regions.