Soil erosion and sediment export under rainfed agriculture dominated landscapes: Model-based evidence from the Didessa watershed, southwestern Ethiopia

Abstract

Global environmental degradation resulting from unsustainable human activities has become a critical development challenge in the 21st century. The Didessa watershed in southwestern Ethiopia, a region dominated by subsistence agriculture, illustrates this vulnerability. This study aims to quantify the spatiotemporal soil loss (SL) and sediment export (SE) from 1987 to 2023 using the RUSLE-InVEST model to inform sustainable watershed management policy. Multitemporal Landsat imagery (1987, 2000, 2013, and 2023) for land use analysis, rainfall, soil texture, conservation practices, and digital elevation model (SRTM) were used to estimate SL and SE (t/ha/yr). The study reveals a dramatically growing erosion crisis, with mean annual soil loss and sediment export increasing by 163% and 367%, respectively, over the study period. A statistical analysis confirmed that a significant (p < 0.001) and steady increase in both measures. The rates of erosion varied across the 26 sub-watersheds, with four identified as severe erosion hotspots, two experiencing a lower rate, and the rest experiencing moderate erosion. The main factors contributing to these variations were rainfall amount, sub-watershed size, slope gradient, and elevation. The estimated cost to rehabilitate the degraded soils and restore the ecosystem services was about USD 24 million. Severe soil loss and sediment export pose a significant threat to agricultural sustainability, water resources, and the functioning of ecosystems. Protect natural vegetation, implement integrated soil and water conservation measures, promote climate-resilient agricultural practices, and assess national-level soil loss reclamation costs based on local data to estimate total soil loss countrywide, as the best recommendations. • Over the 36 years, mean annual soil loss and sediment export in the watershed increased by 163% and 367%, respectively. • The watershed degradation was correlated with agricultural and settlement expansion areas. • The estimated rehabilitation costs to address the observed degradation exceed US$24 million.