Addis Ababa, Ethiopia
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Bekele D.,Ethiopian Institute of Agricultural Research | Alamirew T.,Water and Land Resource Center | Kebede A.,Haramaya University | Zeleke G.,Water and Land Resource Center | Melese A.M.,Florida International University
Journal of Water and Climate Change | Year: 2017

The national economy and food security of many sub-Saharan countries relies on rain-fed agriculture, hence the impact of rainfall variability is highly significant. The intent of this study is to characterize rainfall variability and trend in Awash River Basin for agricultural water management using standard rainfall statistical descriptors. Long-term climate data of 12 stations were analyzed. Onset and cessation dates, length of growing period (LGP) and probability of dry spell occurrences were analysed using INSTAT Plus software. The Mann–Kendall test and the Sen’s slope method were used to assess the statistical significance of the trend. The results show high variability of rainfall (38–73%), LGP (30–38 days) and high probability of dry spell occurrence (up to 100%) during the Belg season (the short rainy season from March to May) compared with the Kiremt season (the main rainy season from June to September) in all stations. Belg season showed a non-significant decline trend in most of the stations, whereas the Kiremt season indicated the contrary. The finding also revealed that supplementary irrigation is vital, especially in the Belg season to cover up to 40% of the crop water requirement deficit. © IWA Publishing 2017.

Yesuf H.M.,Wollo University | Melesse A.M.,Florida International University | Zeleke G.,Water and Land Resource Center | Alamirew T.,Water and Land Resource Center
Environmental Earth Sciences | Year: 2016

Appropriate implementation of Soil and Water Assessment Tool (SWAT) hydrologic model requires prediction uncertainty analysis, calibration and validation of the model against historical output records. Sequential Uncertainty Fitting-2 (SUFI-2) and Generalized Likelihood Uncertainty Estimation (GLUE) algorithms with ArcSWAT2009 and ArcGIS10.0 were used in this research to conduct uncertainty analysis, calibration and validation of the SWAT model using monthly observed streamflow data in Maybar experimental watershed, Ethiopia. The results revealed that the model was generally satisfactory as proved by the uncertainty, calibration and validation goodness of fit indicators: The goodness of fit and the degree to which the calibrated SWAT model accounted for the uncertainties assessed by: P-factor (72, 70 %) and (65, 69 %) for (calibration, validation) stages of SUFI-2 and GLUE algorithms, respectively, and R-factor (0.97, 0.90) and (0.89, 0.95) for (calibration, validation) stages of SUFI-2 and GLUE algorithms, respectively, are reached acceptable values, then the parameter uncertainties used were the desired parameter ranges. Further model evaluation statistics: Coefficient of Determination (R2 ≥ 0.76), Nash–Sutcliffe efficiency (NSE ≥ 0.63), Percent Bias (PBIAS ≤ ± 7.10 %) and Root Mean Square Error-observations Standard deviation Ratio (RSR ≤ 0.46) for both calibration and validation periods were quantified and the extent of similarity between predicted and recorded streamflow data suggests that SWAT model can adequately simulate monthly streamflow at Maybar gauged watershed. © 2016, Springer-Verlag Berlin Heidelberg.

Birhanu K.,Haramaya University | Alamirew T.,Water and Land Resource Center | Olumana Dinka M.,Tshwane University of Technology | Ayalew S.,Addis Ababa Institute of Technology | Aklog D.,Tottori University
Water Resources Management | Year: 2014

One of typical problems in water resources system modeling is derivation of optimal operating policy for reservoir to ensure water is used more efficiently. This paper introduces optimization analysis to determine monthly reservoir operating policies for five scenarios of predetermined cropping patterns for Koga irrigation scheme, Ethiopia. The objective function of the model was set to minimize the sum of squared deviation (SSD) from the desired targeted supply. Reservoir operation under different water availability and thresholds of irrigation demands has been analyzed by running a chance constraint nonlinear programming model based on uncertain inflow data. The model was optimized using Microsoft Excel Solver. The lowest SSD and vulnerability, and the highest volumetric reliability were gained at irrigation deficit thresholds of 20 % under scenario I, 30 % under scenario II, III and V, and at 40 % under scenario IV when compensation release is permitted for downstream environment. These thresholds of deficits could be reduced by 10 % for all scenarios if compensation release is not permitted. In conclusion the reservoir water is not sufficient enough to meet 100 % irrigation demand for design command areas of 7,000 ha. The developed model could be used for real time reservoir operation decision making for similar reservoir irrigation systems. In this specific case study system, attempt should be made to evaluate the technical performance of the scheme and introduce a regulated deficit irrigation application. © 2014, Springer Science+Business Media Dordrecht.

Roth V.,University of Bern | Roth V.,Water and Land Resource Center | Lemann T.,University of Bern | Lemann T.,Water and Land Resource Center
Hydrology and Earth System Sciences | Year: 2016

Accurate rainfall data are the key input parameter for modelling river discharge and soil loss. Remote areas of Ethiopia often lack adequate precipitation data and where these data are available, there might be substantial temporal or spatial gaps. To counter this challenge, the Climate Forecast System Reanalysis (CFSR) of the National Centers for Environmental Prediction (NCEP) readily provides weather data for any geographic location on earth between 1979 and 2014. This study assesses the applicability of CFSR weather data to three watersheds in the Blue Nile Basin in Ethiopia. To this end, the Soil andWater Assessment Tool (SWAT) was set up to simulate discharge and soil loss, using CFSR and conventional weather data, in three small-scale watersheds ranging from 112 to 477 ha. Calibrated simulation results were compared to observed river discharge and observed soil loss over a period of 32 years. The conventional weather data resulted in very good discharge outputs for all three watersheds, while the CFSR weather data resulted in unsatisfactory discharge outputs for all of the three gauging stations. Soil loss simulation with conventional weather inputs yielded satisfactory outputs for two of three watersheds, while the CFSR weather input resulted in three unsatisfactory results. Overall, the simulations with the conventional data resulted in far better results for discharge and soil loss than simulations with CFSR data. The simulations with CFSR data were unable to adequately represent the specific regional climate for the three watersheds, performing even worse in climatic areas with two rainy seasons. Hence, CFSR data should not be used lightly in remote areas with no conventional weather data where no prior analysis is possible. © Author(s) 2016.

Ambachew S.,Sekota Dryland Agricultural Research Center | Alamirew T.,Water and Land Resource Center | Melese A.,Florida International University
Agricultural Water Management | Year: 2014

Knowing the performance of short season crops under deficit irrigation has a paramount importance for arid and semi-arid regions with limited access to on-farm water harvesting or other irrigation infrastructure. In this research, the performance of mungbean, a newly introduced crop into the cropping systems in Ethiopia, to stage-wise and uniform deficit irrigation was tested at Sekota Dryland Agricultural Research Center, Northern Ethiopia. Eight treatments - four stage-wise deficit and four uniform deficit irrigation applications were evaluated during the 2010/2011 dry season. Plant phenological variables, grain yield and irrigation water use efficiency were used for performance evaluation. The results showed that a uniform water stress shortened the dates to 50% flowering and maturity, but with proportionate reduction in yield. The yield obtained varied between 1366kg/ha under 331mm optimal seasonal irrigation to 492kg/ha when one-fourth of ETc (102mm) was uniformly applied though out the growing season. The flowering/reproductive stage was noted as the most sensitive growth stage with a 24.9% yield reduction compared to the control treatment. In all other stages, yield is linearly associated (R2=0.93) with the amount of irrigation water applied, over the range tested. IWUE values ranged from 0.248 to 0.304kg/m3. It can therefore be concluded that provided stress at the midseason stage is avoided and depending on the volume of water available, different deficit irrigation arrangements using on-farm pond water is possible. © 2014 Elsevier B.V.

Roth V.,Center for Development and Environment | Roth V.,University of Bern | Nigussie T.K.,Water and Land Resource Center | Lemann T.,Center for Development and Environment | Lemann T.,University of Bern
Environmental Earth Sciences | Year: 2016

Distributed hydrological models are increasingly used to describe the spatiotemporal dynamics of water and sediment fluxes within basins. In data-scarce regions like Ethiopia, oftentimes, discharge or sediment load data are not readily available and therefore researchers have to rely on input data from global models with lower resolution and accuracy. In this study, we evaluated a model parameter transfer from a 100 hectare (ha) large subwatershed (Minchet) to a 4800 ha catchment in the highlands of Ethiopia using the Soil and Water Assessment Tool (SWAT). The Minchet catchment has long-lasting time series on discharge and sediment load dating back to 1984, which were used to calibrate the subcatchment before (a) validating the Minchet subcatchment and (b) through parameter transfer validating the entire Gerda watershed without prior calibration. Uncertainty analysis was carried out with the Sequential Uncertainty Fitting-2 (SUFI-2) with SWAT-Cup and ArcSWAT2012. We used a similarity approach, where the complete set of model parameters is transposed from a donor catchment that is very similar regarding physiographic attributes (in terms of landuse, soils, geology and rainfall patterns). For calibration and validation, the Nash-Sutcliff model efficiency, the Root Mean Square Error-observations Standard Deviation Ratio (RSR) and the Percent Bias (PBIAS) indicator for model performance ratings during calibration and validation periods were applied. Goodness of fit and the degree to which the calibrated model accounted for the uncertainties were assessed with the P-factor and the R-factor of the SUFI-2 algorithm. Results show that calibration and validation for streamflow performed very good for the subcatchment as well as for the entire catchment using model parameter transfer. For sediment loads, calibration performed better than validation and parameter transfer yielded satisfactory results, which suggests that the SWAT model can be used to adequately simulate monthly streamflow and sediment load in the Gerda catchment through model parameter transfer only. © 2016, Springer-Verlag Berlin Heidelberg.

Gebere S.B.,TU Bergakademie Freiberg | Alamirew T.,Water and Land Resource Center | Merkel B.J.,TU Bergakademie Freiberg | Melesse A.M.,Florida International University
Remote Sensing | Year: 2015

Accurate estimation of rainfall in mountainous areas is necessary for various water resource-related applications. Though rain gauges accurately measure rainfall, they are rarely found in mountainous regions and satellite rainfall data can be used as an alternative source over these regions. This study evaluated the performance of three high-resolution satellite rainfall products, the Tropical Rainfall Measuring Mission (TRMM 3B42), the Global Satellite Mapping of Precipitation (GSMaP_MVK+), and the Precipitation Estimation from Remotely-Sensed Information using Artificial Neural Networks (PERSIANN) at daily, monthly, and seasonal time scales against rain gauge records over data-scarce parts of Eastern Ethiopia. TRMM 3B42 rain products show relatively better performance at the three time scales, while PERSIANN did much better than GSMaP. At the daily time scale, TRMM correctly detected 88% of the rainfall from the rain gauge. The correlation at the monthly time scale also revealed that the TRMM has captured the observed rainfall better than the other two. For Belg (short rain) and Kiremt (long rain) seasons, the TRMM did better than the others by far. However, during Bega (dry) season, PERSIANN showed a relatively good estimate. At all-time scales, noticing the bias, TRMM tends to overestimate, while PERSIANN and GSMaP tend to underestimate the rainfall. The overall result suggests that monthly and seasonal TRMM rainfall performed better than daily rainfall. It has also been found that both GSMaP and PERSIANN performed better in relatively flat areas than mountainous areas. Before the practical use of TRMM, the RMSE value needs to be improved by considering the topography of the study area or adjusting the bias. © 2015 by the authors.

Shimelis B.G.,TU Bergakademie Freiberg | Merkel B.,TU Bergakademie Freiberg | Agumassie T.A.,Water and Land Resource Center
FOG - Freiberg Online Geoscience | Year: 2015

The knowledge of land use and land cover is important for properly managing, planning and monitoring natural resources. The aim of this study was to generate land use maps for the study area and to understand the land use and land cover changes using remotely sensed satellite imageries from 1985 to 2011. The images were geometrically corrected to a common map projection followed by image processing operations. In ERDAS, supervised classification based on the maximum likelihood algorithm was applied to the Landsat images acquired in 1985, 1995, 2006 and 2011. To check the accuracy of the classification, ground truth data was also collected. Post classification change detection was applied in order to assess changes in land use and land cover over time using IDRISI software. Rapid population growth has created land use misbalances. The results showed that dramatic changes in land use and land cover have occurred with shrinkage of water bodies, cultivated land, forests and grassland and at the same time expansion of Catha edulis (chat)/shrubs as well as settlement areas. The result revealed that an absolute shrinkage and loss of water bodies has occurred due to an extensive and massive clearance of forests and grasslands. Between 1985 and 2011, forests became smaller and more fragmented and declined from 202.6 ha to 101.6 ha. Only patches of mature forests are left. They are under threat from expansion of land for chat production and settlements. In the mentioned period, the total area of water bodies decreased from 3.5 % to 1.0 % while the area of grassland and cultivated land decreased from 29.2 % to 19.6 % and 42.4 % to 32.6 %, respectively. For a sustainable development of the watershed resources, proper land use planning is essential. © 2015, Technical University Freiberg. All rights reserved.

Lemann T.,University of Bern | Zeleke G.,University of Bern | Zeleke G.,Water and Land Resource Center | Amsler C.,University of Bern | And 3 more authors.
Applied Geography | Year: 2016

Soil and water conservation (SWC) can influence the amount of sediment yield leaving a catchment and the availability of water for up- and downstream stakeholders. The extent of this influence depends heavily on hydro-climatic conditions in the upstream catchments. This study investigated the changes in blue and green water distribution and sediment yield in a meso-scale catchment in the Wet Wenya Dega agro-climatic zone in the upper Blue Nile basin, where the implementation of SWC measures has been documented for the last 29 years. We implemented the temporal and spatial variability of SWC in the form of terracing into the Soil and Water Assessment Tool (SWAT) and modelled its influence on discharge and sediment load. Using the Sequential Uncertainty Fitting program (SUFI-2), we calibrated and validated discharge and sediment load with a 31-year data set from a sub-catchment (113 ha) and validated the model for the entire catchment (4818 ha) with a two-year data set. Modelling showed that discharge at the catchment level, and thus water availability for downstream stakeholders, did not change significantly with the implementation of new SWC measures, but SWC could substantially reduce sediment yield. Two modelled SWC scenarios showed that with the implementation of SWC measures the average annual sediment yield of the study area could be reduced from 37 t/ha to 17 t/ha. © 2016 Elsevier Ltd.

Gessesse G.D.,Water and Land Resource Center | Mansberger R.,University of Natural Resources and Life Sciences, Vienna | Klik A.,University of Natural Resources and Life Sciences, Vienna
Journal of Mountain Science | Year: 2015

Application of simple and locally based erosion assessment methods that fit to the local condition is necessary to improve the performance and efficiency of soil conservation practices. In this study, rill erosion formation and development was investigated on the topo-sequence of three catchments (300–500 m slope length); and on agricultural fields (6 m and 14 m slope lengths) with different crop-tillage surfaces during erosive storms. Rill density and rill erosion rates were measured using rill cross section survey and close range digital photogrammetry. Rill formation and development was commonly observed on conditions where there is wider terrace spacing, concave slope shapes and unstable stone terraces on steep slopes. At field plot level, rill development was controlled by the distribution and abrupt change in the soil surface roughness and extent of slope length. At catchment scale, however, rill formation and development was controlled by landscape structures, and concavity and convexity of the slope. Greater rill cross sections and many small local rills were associated to the rougher soil surfaces. For instance, relative comparison of crop tillage practices have showed that faba-bean tillage management was more susceptible to seasonal rill erosion followed by Teff and wheat tillage surfaces under no cover condition. Surface roughness and landscape structures played a net decreasing effect on the parallel rill network development. This implies that spatial and temporal variability of the rill prone areas was strongly associated with the nature and initial size of surface micro-topography or tillage roughness. Thus, it is necessary to account land management practices, detail micro-topographic surfaces and landscape structures for improved prediction of rill prone areas under complex topographic conditions. Application of both direct rill cross section survey and close range digital photogrammetric techniques could enhance field erosion assessment for practical soil conservation improvement. © 2015, Science Press, Institute of Mountain Hazards and Environment, CAS and Springer-Verlag Berlin Heidelberg.

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