Soil erosion under climate and land-use change scenarios: An integrated modelling approach for the Upper Blue Nile Basin

Study Region The study was conducted in the Gumara–Maksegnit watershed of the Upper Blue Nile Basin, Ethiopia, an erosion-prone landscape that drains into Lake Tana, a hydrologically and ecologically critical freshwater system. The region is characterized by steep escarpments, highly erodible soils, and rapidly expanding agriculture, making it a hotspot of sediment generation and land degradation within the basin. Study Focus This study assessed past (2003), present (2023), and future (2083) soil erosion by integrating the RUSLE model with ANN-based LULC simulations, Bayesian Model Averaging of five CORDEX RCMs, and bias-corrected rainfall projections. Land-use analysis showed agricultural land expanding from 53.6% (2003) to 68.7% (2023) and projected to reach 72.1% (2083), with corresponding declines in forest and grazing areas. Rainfall erosivity increased from a range of 565–647 to 613–689 MJ mm ha⁻¹ h⁻¹ yr⁻¹ , and is projected to rise to 756–853 (RCP4.5) and 809–907 (RCP8.5) by 2083. Mean annual soil loss increased from 30.1 t ha⁻¹ yr⁻¹ in 2003 to 39.2 t ha⁻¹ yr⁻¹ in 2023, and is projected to reach 42 t ha⁻¹ yr⁻¹ under land-use change alone, 43.4 and 45.9 t ha⁻¹ yr⁻¹ under RCP 4.5 and RCP 8.5 climate scenarios, and 46.3 and 49.2 t ha⁻¹ yr⁻¹ when both drivers are combined. New Hydrological Insights for the Region Future soil loss will increase by up to 63.5% under the combined LUC + RCP8.5 scenario, with steep northern and northeastern slopes remaining persistent erosion hotspots. Topography (LS: 39.6%) is the dominant erosion driver, while high C and P values on cultivated slopes intensify sediment generation. The results show that climate change has a stronger marginal impact than land-use change and that their interaction amplifies erosion non-linearly, underscoring the need for slope-focused, climate-adaptive soil and water conservation to protect the hydrological stability of Lake Tana.