Quantifying the impacts of spatiotemporal land use and land cover changes on soil loss across agroecologies and slope categories using GIS and RUSLE model in Zoa watershed, southwest Ethiopia

Background Soil erosion in Ethiopian highlands is highly consistent with land use/land cover (LULC) changes that are associated with deforestation and a decline in biodiversity. However, identifying soil erosion-prone areas and quantifying soil loss in rugged terrains and various agroecologies due to LULC changes have not been dedicated to scientific studies. Therefore, we quantified the impacts of spatiotemporal LULC changes on soil loss across agroecologies and slope categories using GIS and RUSLE model from 1985 to 2021 in Zoa watershed, southwest Ethiopia. Moreover, prioritizing erosion severity risks at sub-watersheds and quantifying temporal sediment yield is essential for better conservation planning. Landsat images, rainfall, Digital Elevation Model, and soil data were obtained from field observations and secondary sources. Results Bareland and farmland have been expanding at the expense of other land use types. The annual soil loss in the watershed ranged from 0 to 113.21 t -ha(-1) year(-1), 0 to 163.16 t ha(-1) year(-1), and 0 to 194.58 t ha(-1) year(-1) with a mean annual soil loss of 21.07, 29.35 and 40.93 t ha(-1) year(-1) in 1985, 2000, and 2021, respectively. Among LULC classes, the highest soil loss was generated from bareland (31.73 t ha(-1) year(-1)) and farmland (27.08 t ha(-1) year(-1)) in 1985 later upsurged to 35.52 t ha(-1) year(-1)and 59.91 t ha(-1) year(-1) in 2021, respectively, due to the maximum susceptibility of soil erosion risks from unprotected surfaces. The results also revealed that the lowland agroecology generated the highest mean soil loss of 24.05 t ha(-1) year(-1) in 1985, 39.74 t ha(-1) year(-1) in 2000, and increased to 57.55 t ha(-1) year(-1) in 2021. Considering the slope categories, the highest and most excruciating soil loss was engendered from steep (35.55-60.78 t ha(-1) year(-1)) and very steep (52.48-72.69 t ha(-1) year(-1)) slope terrains during 1985-2021. The northwestern part of the watershed is the most erosion-prone area which is now expanding to the central and western parts of the watershed. The sediment yield increased at the fastest rate at the watershed outlet, from 39.3% in 1985 to 94.26% in 2021. Conclusions The results of this study indicated that the conversion of other LULC categories into farmland was the most detrimental to a watershed in terms of soil loss, which necessitates the implementation of appropriate soil and water conservation measures with effective design by considering spatial variability to reduce soil erosion hazards.

Automated summary

Soil erosion in the Ethiopian highlands is closely related to land use/land cover changes, such as deforestation and declining biodiversity. This study used GIS and RUSLE model to quantify the impacts of spatiotemporal land use/land cover changes on soil loss in the Zoa watershed from 1985 to 2021. The results showed that the expansion of bareland and farmland has led to increased soil loss, with the highest rates observed in unprotected surfaces, steep slopes, and the lowland agroecology. Effective soil and water conservation measures are needed to reduce soil erosion hazards.