TRENDS OF COMMUNITY-BASED INTERVENTIONS ON SUSTAINABLE WATERSHED DEVELOPMENT IN THE ETHIOPIAN HIGHLANDS, THE GUMARA WATERSHED

Soil erosion is the driver of food insecurity and environmental degradation affecting the lives of smallholder farmers. To tackle soil and water degradation government-led large-scale soil and water management programs have been introduced at a watershed scale. The long-term viability of those practices in the Gumara watershed remains a major challenge. The objective of the study was to better understand the general approaches used to implement and design watershed management practices so that soil and nutrient transport to downstream water bodies could be managed. Sub watersheds from the large Gumara watershed were identified for detailed study based on erosion hotspots using the SWAT model. These sub-watersheds represent communities organized for conservation works in the absence of food assistance programs. The data were collected from four focus groups of fifty participants each, field observation, and desk-level meetings with experts. A structured questionnaire was used to get relevant information to the participating farmers. According to the findings, each of the selected watersheds used similar approaches to implement conservation activities. The community withdrew from conservation efforts, even on their farm fields, since the success rate was below the expectation. At this spot realizing the long-term benefits of watershed development activities stayed challenging. The smallholder farmer, on the other hand, clearly relies on rain-fed agriculture and hopes to see immediate results to feed his family. In conclusion, government-led development programs have not been evaluated, technically supported, lack trusted in the community and hence development efforts were put in jeopardy.

Runoff and soil loss responses of cultivated land managed with graded soil bunds of different ages in the Upper Blue Nile basin, Ethiopia

Background In view of a wide range of on-site and off-site impacts of soil erosion, different soil and water conservation measures have been implemented mainly over the last two decades in the Gumara watershed and Ethiopia at large. But their effects have not been sufficiently documented, and maintenance of structures received very little attention. This study investigated the effectiveness of graded soil bunds of zero and 11 years of age in reducing runoff and soil loss. Six hydrologically isolated experimental runoff plots (three treatments × two replicates) were prepared to observe rainfall, runoff, and sediment concentrations in the 2019 summer rainfall season (covering approximately 70% of the annual rainfall). Results Newly constructed soil bunds reduced runoff by 34.94 and 25.56% compared to the old and non-treated counterparts, respectively. Similarly, 59.6 and 48.3% soil loss reductions were observed. The amount of soil loss in non-treated plots was twice that from the new plots and even 1.6 times higher than that from the old-graded soil bund treatments. The rate of soil loss in the new- and old-graded soil bund-treated and non-treated plots was 23.5, 45.6, and 58.1 t ha−1 year−1, respectively. However, the effectiveness of the old soil bunds was much lower (only − 12.6 and − 21.7% in runoff and soil loss, respectively) than its new equivalent. Graded soil bunds, in its new form, reduced runoff, runoff coefficient, and soil loss significantly (P < 0.05). Regardless of the treatments, from the start of the rainy season to the end, runoff and runoff coefficient showed an increase, but sediment concentration decreased. Newly constructed soil bund is the most effective in reducing runoff and soil loss. Conclusion Graded soil bunds reduced runoff and soil loss significantly, but the rate even in the treated plots was very high when compared to both the soil loss tolerance (1–6 t ha−1 year−1) and formation rate (10–14 t ha−1 year−1) estimated for the area. Hence, these structures need to be supported by other measures such as grass strips, agro-forestry, and percolation ditches, for better results. Besides, regular maintenance by either removing sediments from bund furrows or increasing the bund height is recommended for sustained reduction of runoff and soil loss.

Change in Stream Flow of Gumara Watershed, upper Blue Nile Basin, Ethiopia under Representative Concentration Pathway Climate Change Scenarios

Climate change plays a pivotal role in the hydrological dynamics of tributaries in the upper Blue Nile basin. The understanding of the change in climate and its impact on water resource is of paramount importance to sustainable water resources management. This study was designed to reveal the extent to which the climate is being changed and its impacts on stream flow of the Gumara watershed under the Representative Concentration Pathway (RCP) climate change scenarios. The study considered the RCP 2.6, RCP 4.5, and RCP 8.5 scenarios using the second-generation Canadian Earth System Model (CanESM2). The Statistical Downscaling Model (SDSM) was used for calibration and projection of future climatic data of the study area. Soil and Water Assessment Tool (SWAT) model was used for simulation of the future stream flow of the watershed. Results showed that the average temperature will be increasing by 0.84 °C, 2.6 °C, and 4.1 °C in the end of this century under RCP 2.6, RCP 4.5, and RCP 8.5 scenarios, respectively. The change in monthly rainfall amount showed a fluctuating trend in all scenarios but the overall annual rainfall amount is projected to increase by 8.6%, 5.2%, and 7.3% in RCP 2.6, RCP 4.5, and RCP 8.5, respectively. The change in stream flow of Gumara watershed under RCP 2.6, RCP 4.5, and RCP 8.5 scenarios showed increasing trend in monthly average values in some months and years, but a decreasing trend was also observed in some years of the studied period. Overall, this study revealed that, due to climate change, the stream flow of the watershed is found to be increasing by 4.06%, 3.26%, and 3.67%under RCP 2.6, RCP 4.5, and RCP 8.5 scenarios, respectively.

Change in Stream Flow of Gumara Watershed, Upper Blue Nile Basin, Ethiopia under Representative Concentration Pathway Climate Change Scenario

Climate change plays a pivotal role in the hydrology of tributaries in the upper Blue Nile basin. This study was designed to reveal the extent to which climate change impacts on stream flow of the Gumara watershed under the Representative Concentration Pathway (RCP) climate change scenario. The study considered the RCP 2.6, RCP 4.5 and RCP 8.5 scenarios using the second generation Canadian Earth System Model (CanESM2). The Statistical Downscaling Model (SDSM) was used for calibration and projection of future climatic data of the study area. Soil and Water Assessment Tool (SWAT) model was used for simulation of the future stream flow of the watershed. Result showed that the average temperature will be increasing by 0.84oC, 2.6oC and 4.1oC in the end of this century under RCP 2.6, RCP 4.5 and RCP 8.5 scenarios respectively. The change in monthly rainfall amount showed a fluctuating trend in all scenarios but the overall annual rainfall amount is projected to increase by 8.6%, 5.2% and 7.3% in RCP 2.6, RCP 4.5, and RCP 8.5 respectively. Overall, this study revealed that, due to climate change, the stream flow of the watershed is found to be increasing by 4.06%, 3.26%, and 3.67% under RCP 2.6, RCP 4.5 and RCP 8.5 scenarios respectively.