Environmental degradation within river basins arises from both natural factors, such as climatic variability and biophysical attributes like topography and soil characteristics, as well as anthropogenic influences. Human-induced degradation, driven by factors such as population growth, urban expansion, and shifts in land use patterns, exacerbates the natural degradation processes. The study sought to model soil erosion risk in the Black Volta River basin. Specifically, the study (1) evaluated and determined the land use and land cover dynamic and drivers of urban expansion in the Wa municipality of Ghana between 1990 and 2020, (2) estimated soil erosion risk in a typical savannah landscape of Wa municipality of Ghana between 1990 and 2020 and (3) estimated and evaluated soil erosion risk across various landscape units of the Black Volta River basin over the periods of 1992, 2006 and 2020. Landsat satellite data (30 x 30 m resolution) was processed using Geographical Information System and remote sensing techniques to establish the spatial and temporal dynamics of land cover in the Wa municipality for the years 1990, 2001, 2010 and 2020. The thematic maps were used to assess the drivers of urban expansion (objective 1) and the potential and soil erosion risk (objective 2) in the Wa municipality. In the basin scale and landscape units’ erosion risk modelling for the years 1992, 2006 and 2020 (objective 3), a 300 x 300 m resolution land cover data from the Copernicus Global Land Cover Services was used. Based on the spatial and temporal analysis of land cover change, it was evident that settlement expansion led to the depletion of woody biomass over the three decades (1990 to 2020). Settlement expansion was influenced by accessibility and connectivity factors, such as distance to existing settlements, rivers, and primary, tertiary, and unclassified roads, which were established as predictors of settlement expansion in the Wa municipality. By employing the Revised Universal Soil Loss Equation model, potential erosion risk was higher in 1990 (mean annual rate = 8.5 t ha⁻¹yr⁻¹) due to higher rainfall erosivity compared to 2020 (6.5 t ha⁻¹yr⁻¹) when rainfall erosivity was lower. However, the estimated soil erosion risk was lower in 1990 (2.6 t ha⁻¹yr⁻¹) due to greater vegetation cover, compared to 2020 (3.1 t ha⁻¹yr⁻¹) when vegetation cover declined. Soil loss was notably high in settlement, urbanising and areas with long and steep slopes, emphasising the influence of human and topographic factors on high erosion risk. This was statistically validated with data from a field survey that measures the spatial extents of soil erosion damages in 2 km² each of settlement, open savannah and closed savannah areas in the Wa municipality. It was established that settlement areas were the most damaged followed by open savannah and closed savannah units. Statistical correlation analysis reveals a positive relationship between the spatial extent of damages and the predicted soil erosion risk rates from the RUSLE model. At the basin scale and across landscape units, erosion risk and soil loss are primarily driven by topographic attributes and rainfall erosivity factors. The Savannah Escarpment and Sahelian Highlands with steep slope characteristics were identified as extreme erosion risk landscape units, while the Low Sahelian Plains and Sahelian Uplands, characterised by flat and gentle slopes, were predicted to have low erosion risk. Also, localised concave areas in the Savannah Escarpment and Sahelian Highland coupled with low TWI characteristics further heightened erosion risk. Additionally, a positive increase in the rainfall erosivity factor resulted in a positive change in soil loss while a decrease in rainfall erosivity factor led to a negative change in soil loss across all the landscape units, thus, underscoring the influence of rainfall erosivity factor on high erosion risk. Overall, the findings enhance the understanding of the erosion risk dynamic in the Black Volta River basin and would serve as a guide in planning management practices in line with global goals that seek to ensure environmental sustainability.
