Climate and Land Use Controls on Future Soil Erosion in the Upper Blue Nile Highlands

Soil erosion in the Ethiopian highlands poses a persistent threat to land productivity, downstream water bodies, and long-term watershed sustainability. While both climate change and land-use transitions are recognized as major drivers of erosion, their combined and relative effects remain insufficiently quantified at watershed scale. This study investigates how projected climate change and land-use change interact to shape future soil erosion dynamics in the Gumara–Maksegnit watershed, a critical tributary of Lake Tana in the Upper Blue Nile Basin. An integrated modeling framework was developed by coupling the Revised Universal Soil Loss Equation (RUSLE) with probabilistic climate projections and data-driven land-use simulations. Future rainfall was derived from five CORDEX-Africa regional climate models, bias-corrected and combined using Bayesian Model Averaging (BMA) to reduce model uncertainty and improve representation of rainfall erosivity. Land-use and land-cover changes were mapped for 2003 and 2023 using multi-temporal Landsat imagery and Random Forest classification, and future land-use patterns (2083) were simulated using an artificial neural network–based Cellular Automata approach. Soil erosion was quantified for historical, current, and future periods under land-use change only, climate change only (RCP4.5 and RCP8.5), and combined scenarios. Results indicate a continued expansion of cultivated land at the expense of forest and grazing areas, accompanied by a progressive increase in rainfall erosivity. Mean annual soil loss increased substantially from historical to current conditions and is projected to intensify further under future scenarios. Climate change exerts a stronger marginal influence on soil erosion than land-use change alone; however, their interaction amplifies erosion non-linearly, leading to the highest erosion rates under the combined land-use change and RCP8.5 scenario. Persistent erosion hotspots are concentrated on steep northern and northeastern slopes, where high topographic control coincides with limited conservation practices. The findings emphasize the importance of integrating climate uncertainty and land-use dynamics in soil erosion assessments and highlight the need for slope-targeted, climate-adaptive soil and water conservation strategies to mitigate future land degradation in the Upper Blue Nile highlands.---Getu Legese Abebaw is funded for his PhD study by the Scholarship for Christian Young People.