Climate change scenarios predict an increase in the frequency of heavy rainfall events in some areas. This will increase runoff and soil erosion, and reduce agricultural productivity, particularly on vulnerable mounta...Climate change scenarios predict an increase in the frequency of heavy rainfall events in some areas. This will increase runoff and soil erosion, and reduce agricultural productivity, particularly on vulnerable mountainous agricultural lands that is already exhibiting high rates of soil erosion. Haphazard implementation of soil and water conservation （SWC） interventions on scattered fields is inefficient in reducing soil erosion. The objective of this study was to identify areas at high risk of erosion to aid the design and implementation of sustainable SWC using GIS analysis and farmers＇ participation approach. A 25 m digital elevation model （DEM） was used to derive layers of flow accumulation, slope steepness and land curvature, which were used to derive an erosion-risk （priority） map for the whole watershed. Boundaries of farmers＇ fields were mapped and verified by the community and each field was classified into high, moderate or low erosion risk. Fields with low flow accumulation （top of hill） and/or steep slope and/or convex slope were assigned high erosion risk and therefore high implementation priority. The study showed that more than 54% of the fields were classified into high erosion risk areas. Accordingly, a community-watershed plan was established, revised and approved by the community.Incentive loans to implement SWC measures were distributed to 100 farmers based on the priorities of their fields. Judged by local farmers and using 16 randomly selected fields, 90% of the targeted areas were correctly identified using the erosion risk map. After two years, the conservation measures had led to marked improvement of soil conservation. The approach is simple and easy to comprehend by the community and provides scientific basis to prioritize the implementation of SWC and to target the most degraded areas, which amplify the impact of these in reducing the vulnerability to land degradation.展开更多
The coincidence of intensive rainfall events at the beginning of the rainy season and unprotected soil conditions after extreme dry spells expose the Ethiopian Highlands to severe soil erosion.Soil and water conservat...The coincidence of intensive rainfall events at the beginning of the rainy season and unprotected soil conditions after extreme dry spells expose the Ethiopian Highlands to severe soil erosion.Soil and water conservation measures(SWC)have been applied to counteract land degradation in the endangered areas,but SWC efficiency may vary related to the heterogeneity of the landscape.The Soil and Water Assessment Tool(SWAT)model was used to model hydrology and sediment dynamics of a 53.7 km^(2)watershed,located in the Lake Tana basin,Ethiopia.Spatially distributed stone bund impacts were applied in the model through modification of the surface runoff ratio and adjustment of a support practice factor simulating the trapped amounts of water and sediment at the SWC structure and watershed level.The resulting Nash-Sutcliffe efficiency(NSE)for daily streamflow simulation was 0.56 for the calibration and 0.48 for the validation period,suggesting satisfactory model performance.In contrast,the daily sediment simulation resulted in unsatisfactory model performance,with the NSE value of 0.07 for the calibration and–1.76 for the validation period and this could be as a result of high intensity and short duration rainfall events in the watershed.Meanwhile,insufficient sediment yield prediction may result to some extent from daily based data processing,whereas the driving runoff events and thus sediment loads occur on sub-daily time scales,probably linked with abrupt gully breaks and development.The calibrated model indicated 21.08 Mg/hm^(2)average annual sediment yield,which is far beyond potential soil regeneration rate.Despite the given limits of model calibration,SWAT may support the scaling up and out of experimentally proven SWC interventions to encourage sustainable agriculture in the Ethiopian Highlands.展开更多
基金the CocaCola foundation and the CGIAR CRP5 program on Water, Land and Ecosystems for supporting this study
文摘Climate change scenarios predict an increase in the frequency of heavy rainfall events in some areas. This will increase runoff and soil erosion, and reduce agricultural productivity, particularly on vulnerable mountainous agricultural lands that is already exhibiting high rates of soil erosion. Haphazard implementation of soil and water conservation （SWC） interventions on scattered fields is inefficient in reducing soil erosion. The objective of this study was to identify areas at high risk of erosion to aid the design and implementation of sustainable SWC using GIS analysis and farmers＇ participation approach. A 25 m digital elevation model （DEM） was used to derive layers of flow accumulation, slope steepness and land curvature, which were used to derive an erosion-risk （priority） map for the whole watershed. Boundaries of farmers＇ fields were mapped and verified by the community and each field was classified into high, moderate or low erosion risk. Fields with low flow accumulation （top of hill） and/or steep slope and/or convex slope were assigned high erosion risk and therefore high implementation priority. The study showed that more than 54% of the fields were classified into high erosion risk areas. Accordingly, a community-watershed plan was established, revised and approved by the community.Incentive loans to implement SWC measures were distributed to 100 farmers based on the priorities of their fields. Judged by local farmers and using 16 randomly selected fields, 90% of the targeted areas were correctly identified using the erosion risk map. After two years, the conservation measures had led to marked improvement of soil conservation. The approach is simple and easy to comprehend by the community and provides scientific basis to prioritize the implementation of SWC and to target the most degraded areas, which amplify the impact of these in reducing the vulnerability to land degradation.
文摘The coincidence of intensive rainfall events at the beginning of the rainy season and unprotected soil conditions after extreme dry spells expose the Ethiopian Highlands to severe soil erosion.Soil and water conservation measures(SWC)have been applied to counteract land degradation in the endangered areas,but SWC efficiency may vary related to the heterogeneity of the landscape.The Soil and Water Assessment Tool(SWAT)model was used to model hydrology and sediment dynamics of a 53.7 km^(2)watershed,located in the Lake Tana basin,Ethiopia.Spatially distributed stone bund impacts were applied in the model through modification of the surface runoff ratio and adjustment of a support practice factor simulating the trapped amounts of water and sediment at the SWC structure and watershed level.The resulting Nash-Sutcliffe efficiency(NSE)for daily streamflow simulation was 0.56 for the calibration and 0.48 for the validation period,suggesting satisfactory model performance.In contrast,the daily sediment simulation resulted in unsatisfactory model performance,with the NSE value of 0.07 for the calibration and–1.76 for the validation period and this could be as a result of high intensity and short duration rainfall events in the watershed.Meanwhile,insufficient sediment yield prediction may result to some extent from daily based data processing,whereas the driving runoff events and thus sediment loads occur on sub-daily time scales,probably linked with abrupt gully breaks and development.The calibrated model indicated 21.08 Mg/hm^(2)average annual sediment yield,which is far beyond potential soil regeneration rate.Despite the given limits of model calibration,SWAT may support the scaling up and out of experimentally proven SWC interventions to encourage sustainable agriculture in the Ethiopian Highlands.
