Comprehensive assessment of soil erosion risk for better land use planning in river basins : case study of the Upper Blue Nile River

In the drought-prone Upper Blue Nile River (UBNR) basin of Ethiopia, soil erosion by water results in significant consequences that also affect downstream countries. However, there have been limited comprehensive studies of this and other basins with diverse agroecologies. We analyzed the variability of gross soil loss and sediment yield rates under present and expected future conditions using a newly devised methodological framework. The results showed that the basin generates an average soil loss rate of 27.5 t ha(-1) yr(-1) and a gross soil loss of ca. 473 Mt yr(-1), of which, at least 10% comes from gully erosion and 26.7% leaves Ethiopia. In a factor analysis, variation in agroecology (average factor score = 1.32) and slope (1.28) were the two factors most responsible for this high spatial variability. About 39% of the basin area is experiencing severe to very severe (>30 t ha(-1) yr(-1)) soil erosion risk, which is strongly linked to population density. Severe or very severe soil erosion affects the largest proportion of land in three subbasins of the UBNR basin: Blue Nile 4 (53.9%), Blue Nile 3 (45.1%), and Jema Shet (42.5%). If appropriate soil and water conservation practices targeted ca. 77.3% of the area with moderate to severe erosion (>15 t ha(-1) yr(-1)), the total soil loss from the basin could be reduced by ca. 52%. Our methodological framework identified the potential risk for soil erosion in large-scale zones, and with a more sophisticated model and input data of higher spatial and temporal resolution, results could be specified locally within these risk zones. Accurate assessment of soil erosion in the UBNR basin would support sustainable use of the basin's land resources and possibly open up prospects for cooperation in the Eastern Nile region

Comprehensive assessment of soil erosion risk for better land use planning in river basins: Case study of the Upper Blue Nile River

In the drought-prone Upper Blue Nile River (UBNR) basin of Ethiopia, soil erosion by water results in significant consequences that also affect downstream countries. However, there have been limited comprehensive studies of this and other basins with diverse agroecologies. We analyzed the variability of gross soil loss and sediment yield rates under present and expected future conditions using a newly devised methodological framework. The results showed that the basin generates an average soil loss rate of 27.5 t ha− 1 yr− 1 and a gross soil loss of ca. 473 Mt yr− 1, of which, at least 10% comes from gully erosion and 26.7% leaves Ethiopia. In a factor analysis, variation in agroecology (average factor score = 1.32) and slope (1.28) were the two factors most responsible for this high spatial variability. About 39% of the basin area is experiencing severe to very severe (> 30 t ha− 1 yr− 1) soil erosion risk, which is strongly linked to population density. Severe or very severe soil erosion affects the largest proportion of land in three subbasins of the UBNR basin: Blue Nile 4 (53.9%), Blue Nile 3 (45.1%), and Jema Shet (42.5%). If appropriate soil and water conservation practices targeted ca. 77.3% of the area with moderate to severe erosion (> 15 t ha− 1 yr− 1), the total soil loss from the basin could be reduced by ca. 52%. Our methodological framework identified the potential risk for soil erosion in large-scale zones, and with a more sophisticated model and input data of higher spatial and temporal resolution, results could be specified locally within these risk zones. Accurate assessment of soil erosion in the UBNR basin would support sustainable use of the basin's land resources and possibly open up prospects for cooperation in the Eastern Nile region

Soil erosion and conservation in Ethiopia : A review

This paper reviews Ethiopia’s experience and research progress in past soil and water conservation (SWC) efforts and suggests possible solutions for improvement. Although indigenous SWC techniques date back to 400 BC, institutionalized SWC activity in Ethiopia became significant only after the 1970s. At least six national SWC related programs have been initiated since the 1970s and their focus over time has shifted from food relief to land conservation and then to livelihoods. The overall current soil erosion rates are highly variable and large by international standards, and sheet, rill, and gully erosion are the dominant processes. The influence of human activities on the landscape has traditionally been deleterious, but this trend seems to have recently reversed in some parts of the country following the engagement of the communities in land management. The efficiency of SWC measures show mixed results that are influenced by the type of measures and the agro-ecology under which they were implemented; in general, the relative performance of the interventions is better in the drylands as compared to humid areas. Methodological limitations also occur when addressing the economic aspects related to benefits of ecosystem services and other externalities. Although farmers have shown an increased understanding of the soil erosion problem, SWC efforts face a host of barriers related to limited access to capital, limited benefits, land tenure insecurity, limited technology choices and technical support, and poor community participation. In general SWC research in Ethiopia is fragmented and not comprehensive, mainly because of a lack of participatory research, field observations, and adoptable methods to evaluate impacts. A potentially feasible approach to expand and sustain SWC programs is to attract benefits from global carbon markets. Moreover, a dedicated institution responsible for overseeing the research–extension linkage of SWC interventions of the country should be established

Take out the farmer: An economic assessment of land expropriation for urban expansion in Bahir Dar, Northwest Ethiopia

In Ethiopia, the demand for land for urbanisation is primarily met by converting rural land through expropriation. However, land expropriations are adversely affecting the previous land users by reducing the amount of production and their sources of income. In Bahir Dar, one of the fastest-growing cities in Ethiopia, approximately 300 landholdings are expropriated each year, on average, for urban expansion. This paper assesses the land expropriations to examine whether they offer economically appropriate compensation for the previous land users. Land expropriations for urbanisation between 2007/2008 and 2016/2017 were analysed based on data on land expropriation and its compensation payment obtained from the Bahir Dar City Land Administration and Management Office. Data were analysed using an exponential growth model and a stochastic budgeting technique in which Monte Carlo simulations are performed. Between 2007/2008 and 2016/2017, more than 1500 ha of land were included in the city's boundary through expropriation from 2900 landholders. The affected farmers received compensation that represents only 37 per cent of the value of current crop yields and its growth. The current compensation scheme ignores the impact of inflation on the prices of crops and assumes constant yields. It also excludes the value of crop residuals. We propose a workable discounted compensation framework that considers crop price and yield growths. This will make the compensation scheme more appropriate and make the affected farmers better off

Curve number calibration for measuring impacts of land management in sub-humid Ethiopia

International audienceStudy Region We investigate the event runoff response in six sub-catchments in the Lake Tana sub-basin, headwater of the Blue Nile basin, northwest Ethiopia. Steep and mountainous terrains surround floodplains, imposing runoff and soil erosion in the upper catchments and flooding and sedimentation at floodplains. This study was conducted in the upland runoff source catchments. Study Focus The focus is to investigate catchment characteristics that control the event runoff response in upland catchments, and how recent land management practices may have contributed to improved hydrological conditions. Event rainfall and runoff data were obtained at five-minute time steps through automated divers and tipping bucket rain gauges and related to catchment characteristics. New Hydrological Insights for the Region Our results show that the catchment event quickflow response was controlled by different factors of both natural and anthropogenic nature of which forest and shrubs, bund density and soil organic matter content were found to be the most important to reduce event quickflow. On the contrary, increase in cropland area caused an increase in quickflow. Through least square fitting procedure of the Natural Resources Conservation Service Curve Number method (NRCS-CN), a site specific abstraction ratio (λ) value of 0.01, rather than the commonly used 0.2 or 0.05, was found to be most appropriate for the sub-humid highlands of Ethiopia

Variability modeling and mapping of soil properties for improved management in Ethiopia

Abstract Managing soils for improved agricultural production requires information on soil fertility status. Our objective was to map for better soil management in Ethiopia and determine their spatial correlation at a separation distance of 29 m. We collected 82 soil samples (0–20 cm depth) at 560 ha of land and determined pH, Olsen extractable phosphorus (Olsen‐P), and organic carbon (OC). We then interpolated between sample points (ordinary kriging‐OK and distance weighting‐IDW [inverse distance weighting]) to evaluate spatial dependence. Olsen‐P ranged from 2.68–42 mg/kg and exhibited high variability with a coefficient of variation (CV) ≥35%. Conversely, soil pH showed low variability (CV ≤ 15%) and ranging from 4.84 to 6.81. Soil OC content varied from 0.81% to 3.17%. The IDW (R2 = 0.86; RMSE = 0.019) outperformed the OK. The semivariogram results indicate a strong dependence for pH and OC for spherical, exponential, and Gaussian models, while moderately spatially auto correlated for Olsen‐P for all models. The IDW and OK predict the spatial variability of the pH (moderately acidic), Olsen‐P (low), and OC (very low) contents. The soil maps may help to improve soil management alternatives, increase crop productivity, and secure environmental quality