Soil Erosion, Sediment Yield, and Mitigation Measures under Climate Change: Case Study of Beressa Watershed, Upper Blue Nile Basin, Ethiopia

Abstract

Soil erosion is a major environmental challenge in Ethiopia, particularly in the Upper Blue Nile Basin, where it contributes to severe land degradation and sediment-related problems. Climate change worsens these problems. However, the links among soil erosion, climate projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6), and mitigation efforts remain poorly understood. This study aimed to assess climate change impacts on soil erosion and sediment yield and to evaluate the effectiveness of best management practices (BMPs) for future climate in the Beressa watershed using the Soil and Water Assessment Tool (SWAT). This study is among the first in the Upper Blue Nile Basin to integrate CMIP6 climate projections with SWAT for evaluating future BMP performance. Both observed and bias-corrected future climate data were used. The MRI-ESM2-0 and BCC-CSM2-MR model were selected based on their superior performance in reproducing observed temperature and precipitation patterns in the study region, respectively. Simulations covered the baseline period (1995–2023), near-term period (2030–2059), and far-term period (2060–2089), under SSP2-4.5 and SSP5-8.5 scenarios. The SWAT model demonstrated satisfactory performance in simulating observed streamflow and sediment yield during calibration and validation. Climate projections indicated increasing temperature and precipitation, leading to higher soil erosion and sediment yield, with shifts in erosion hotspot areas. Sediment yield is projected to increase under both SSP2-4.5 (32% near-term, 27.9% far-term) and SSP5-8.5 (19.2% near-term, 45.4% far-term) compared to the baseline. BMP evaluation showed sediment-yield reductions by terracing (48.36–50.64%), conservation agriculture (29.70–32.76%), contour farming (19.65–20.40%), and combined use (58.20–59.86%). Variations among sub-watersheds highlighted the influence of local watershed characteristics on erosion response to climate change and on the effectiveness of BMPs. These findings enhance understanding of climate-driven erosion processes and support the development of adaptive conservation strategies