Assessing hydrological interactions, soil erosion intensities, and vegetation dynamics in Nyabarongo River tributaries: a SWAT and RUSLE modeling approach

Soil, water, and vegetation are essential, particularly in the tributaries draining into the waterbodies. The Nyabarongo River basin in Rwanda faces significant challenges related to soil erosion and hydrological processes. Understanding the interactions between soil, water, and vegetation is crucial for effective watershed management and conservation efforts. This study aims to assess these dynamics using the SWAT and RUSLE models, focusing on the tributaries of the Nyabarongo River. The Global Climate Model-derived scenarios are incorporated into the SWAT model to predict changes in streamflow and evapotranspiration. Additionally, an asset of statistical measurements covering 34 years is used to analyze vegetation greenness using the Normalized Differences Vegetation Index (NDVI3g). The SWAT model revealed stable stream flow (45 –100 m 3 s −1 ) and unstable stream flow with flood peaks > 100 m 3 s −1 in the specific tributaries. The model also predicted changes, including an annual increase in streamflow (1.8–13.6%) and evapotranspiration (3.3–14.3%) across all tributaries. Both SWAT-MUSLE and RUSLE simulations indicate relatively similar soil erosion intensities, with very high soil erosion (50–59 t ha −1 y −1 ) and (50–56.12 t ha −1 y −1 ), respectively. The analysis of vegetation cover indicates that a significant portion of the studied area exhibits degraded vegetation. With the exception of the Bakokwe tributary, which showed a positive correlation. The remaining tributaries indicated a negative correlation between the NDVI and sediment yield. The study identifies significant correlations between sediment yield, vegetation cover, and hydrological processes in the tributaries of the Nyabarongo River. The findings highlight the importance of vegetation management in mitigating soil erosion and maintaining water quality. Decision makers can use these insights to develop targeted soil erosion conservation measures for the Nyabarongo River basin.