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Search Results: 1 - 10 of 144514 matches for " Berhanu F. Alemaw "
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Resilience, reliability and risk analyses of maize, sorghum and sunflower in rain-fed systems using a soil moisture modeling approach  [PDF]
Berhanu F. Alemaw
Agricultural Sciences (AS) , 2012, DOI: 10.4236/as.2012.31015
Abstract: This paper is aimed at examining the applicability of methods for resilience, reliability and risk analyses of rain-fed agricultural systems from modeled continuous soil moisture availability in rain-fed crop lands. The methodology involves integration of soil and climatic data in a simple soil moisture accounting model to assess soil moisture availability, and a risk used as indicator of sustainability of rain-fed agricultural systems. It is also attempted to demonstrate the role of soil moisture modeling in risk analysis and agricultural water management in a semi-arid region in Limpopo Basin where rain-fed agriculture is practiced. For this purpose, a daily-time step soil moisture accounting model is employed to simulate daily soil moisture, evaporation, surface runoff, and deep percolation using 40 years (1961-2000) of agroclimatic data, and cropping cycle data of maize, sorghum and sunflower. Using a sustainability criterion on crop water requirement and soil moisture availability, we determined resilience, risk and reliability as a quantitative measure of sustainability of rain-fed agriculture of these three crops. These soil moisture simulations and the sustainability criteria revealed further confirmation of the relative sensitivity to drought of these crops. Generally it is found that the risk of failure is relatively low for sorghum and relatively high for maize and sunflower in the two sites with some differences of severity of failure owing to the slightly different agroclimatic settings.
Hydrological Modeling of Large Drainage Basins Using a GIS-based Hybrid Atmospheric and Terrestrial Water Balance (HATWAB) Model  [PDF]
Berhanu F. Alemaw
Journal of Water Resource and Protection (JWARP) , 2012, DOI: 10.4236/jwarp.2012.47060
Abstract: A Hydrological model is proposed to study the spatial and temporal variability of the water budget components of large drainage basin systems from atmospheric and terrestrial water balances. In order to understand the water balances that include, surface runoff, actual evapotranspiration and soil moisture, a GIS-based simple water balance model which is referred as Hydrological Model from Hybrid Atmospheric and Terrestrial Water Balances with acronym HATWAB is presented. The spatio-temporal climatology database was created from a network of climate stations from CLIMWAT data base to reconstruct the monthly primary inputs to HATWAB model, rainfall and potential evapotranspiration. The modeling principles and HATWAB model are demonstrated using the Limpopo and Congo basins in Africa. The model was used to simulate water balance components by taking rainfall-runoff processes in the basin including soil-texture controlled moisture in the terrestrial system, and the vertical integrated moisture convergence that accounts for the net water vapor flux from the basins in order to close the hydrologic water budget.
Climate Change Impacts and Adaptation in Rainfed Farming Systems: A Modeling Framework for Scaling-Out Climate Smart Agriculture in Sub-Saharan Africa  [PDF]
Berhanu F. Alemaw, Timothy Simalenga
American Journal of Climate Change (AJCC) , 2015, DOI: 10.4236/ajcc.2015.44025
Abstract: Improving agricultural water productivity, under rainfed or irrigated conditions, holds significant scope for addressing climate change vulnerability. It also offers adaptation capacity needs as well as water and food security in the southern African region. In this study, evidence for climate change impacts and adaptation strategies in rainfed agricultural systems is explored through modeling predictions of crop yield, soil moisture and excess water for potential harvesting. The study specifically presents the results of climate change impacts under rainfed conditions for maize, sorghum and sunflower using soil-water-crop model simulations, integrated based on daily inputs of rainfall and evapotranspiration disaggregated from GCM scenarios. The research targets a vast farming region dominated by heavy clay soils where rainfed agriculture is a dominant practice. The potential for improving soil water productivity and improved water harvesting have been explored as ways of climate change mitigation and adaptation measures. This can be utilized to explore and design appropriate conservation agriculture and adaptation practices in similar agro-ecological environments, and create opportunities for outscaling for much wider areas. The results of this study can suggest the need for possible policy refinements towards reducing vulnerability and adaptation to climate change in rainfed farming systems.
Assessment of Sedimentation Impacts on Small Dams—A Case of Small Reservoirs in the Lotsane Catchment  [PDF]
Berhanu F. Alemaw, Malebogo Majauale, Timoty Simalenga
Journal of Water Resource and Protection (JWARP) , 2013, DOI: 10.4236/jwarp.2013.512118
Abstract:

Sedimentation is a major problem for agricultural dams in Botswana, as it reduces the storage capacity and life span of the reservoirs. The process of sedimentation starts from day one of the impounding of water in any given reservoir. Even though a provision is made for every reservoir during planning for a certain storage capacity, specifically for sediment deposition, called dead storage, a major portion of the sediment gets deposited for many years of the reservoir’s life in areas other than the dead storage, and this trend cannot be reversed at easy cost. This study is aimed at the analysis of prevailing sedimentation processes in the nearby dozens of dams found in the Lotsane catchment located within the Limpopo Basin of Botswana, and focuses on assessment of annual sedimentation rate. A spatial analysis and modelling study was conducted based on the Revised Universal Soil Loss Equation and GIS to determine sediment yield and degree of impact of each reservoir for a given landscape, rainfall and catchment heterogeneity. Field observations and soil sampling were carried out in order to determine the factors that lead to reservoir sedimentation. Spatial data on the dams in Lotsane catchment were also collected from Ministry of Agriculture, which were used for ground-truthing, GIS-based calculations and model validation. The average sediment rate and sediment delivery ratio were found to be 1.74 t/ha/year and 81%, respectively. These are useful parameters to estimate service life of the dams and plan remedial measures related to sedimentation problems.

Regionalization of Rainfall Intensity-Duration-Frequency (IDF) Curves in Botswana  [PDF]
Berhanu F. Alemaw, Ron T. Chaoka
Journal of Water Resource and Protection (JWARP) , 2016, DOI: 10.4236/jwarp.2016.812088
Abstract: A regional analysis of design storms, defined as the expected rainfall intensity for given storm duration and return period, is conducted to determine storm Rainfall Intensity-Duration-Frequency (IDF) relationships. The ultimate purpose was to determine IDF curves for homogeneous regions identified in Botswana. Three homogeneous regions were identified based on topographic and rainfall characteristics which were constructed with the K-Means Clustering algorithm. Using the mean annual rainfall and the 24 hr annual maximum rainfall as an indicator of rainfall intensity for each homogeneous region, IDF curves and maps of rainfall intensities of 1 to 24 hr and above durations were produced. The Gamma and Lognormal probability distribution functions were able to provide estimates of rainfall depths for low and medium return periods (up to 100 years) in any location in each homogeneous region of Botswana.
Regional Design Storm and Flood Modelling—Risk Implications in Ungauged Catchments  [PDF]
Berhanu F. Alemaw, Ron T. Chaoka
Journal of Water Resource and Protection (JWARP) , 2016, DOI: 10.4236/jwarp.2016.813093
Abstract: Most planned developments in a catchment for control of excess water using a culvert, bridge or dam spillway are located at a site in a stream where there are no discharge measurements. Even though, for gauged catchments a number of established flood frequency models and rainfall-runoff models do exist, for ungauged catchments mostly regional flood frequency and event-based rainfall-runoff models are used, which depend on regional parameters. In this paper, a regional approach for design floods is presented and risk implication for design of drainage structures assessed. A case study in light of the above has been considered at four ungauged sites in the Limpopo Drainage Basin in north-eastern Botswana.
Regional Drought Severity Assessment at a Basin Scale in the Limpopo Drainage System  [PDF]
Berhanu F. Alemaw, J. M. Kileshye-Onema, D. Love
Journal of Water Resource and Protection (JWARP) , 2013, DOI: 10.4236/jwarp.2013.511116
Abstract:

A spatial analysis of drought characteristics in the Limpopo basin is undertaken to evaluate its regional implications to water management challenges. In this study, drought duration, frequency and severity are investigated. In addition drought Severity-Area-Frequency (SAF) curves were constructed. The entire Limpopo River Basin is subdivided into four homogeneous regions based on topographic and climate variations in the basin, which was constructed with the K-Means Clustering algorithm. Using the medium range time series of the Standardized Precipitation Index (SPI) as an indicator of drought for each homogeneous region, monthly and annual SAF curves and maps of probability of drought occurrence were produced. The results indicated localized severe droughts in higher frequencies compared to moderate to severe low frequency droughts spread over wider areas in the basin. The approach can be used to develop improved drought indicators to assess the relationship between drought hazard and vulnerability and to enhance the performance of methods currently used for drought forecasting. In general, this preliminary investigation reveals that the western part of the basin will face a higher risk of drought when compared to other regions of the Limpopo Basin in terms of the medium-term drought patterns. The Limpopo Basin is water stressed and livelihood challenges remain high, thus impacts of droughts and related resilience options should be taken into account in the formulation of regional sustainable water resources development strategies.

Investigating the causes of water-well failure in the Gaotlhobogwe wellfield in southeast Botswana
Ron T Chaoka, Berhanu F Alemaw, Loago Molwalelfhe, Oteng M Moreomongwe
Journal of Applied Sciences and Environmental Management , 2006,
Abstract: In the management of groundwater resources, identifying determinants of borehole failure is useful in planning borehole and wellfield remedial measures as well identifying appropriate water treatment mechanisms if deteriorating water quality prevails as a result of decline of borehole yield and water level. A continually declining well yield in the Gaotlhobogwe wellfield, in south eastern Botswana, triggered this investigation. The determinants of groundwater level decline, which reaches about 80% in the wellfield were identified and their contribution assessed through multivariate analysis. Even though there is a 50% of decline in the specific capacity of pumping wells within 8 years period from 1995- 2003, another 30% of the decline was found to be attributed to chemical determinants, namely as Mn, Mg, Fe NO3, HCO3, CO3 and SO4. The potential physical determinants are found to be pH, Ec and TDS. The geological and hydro-geological evidence of the possible causes of groundwater decline and the identified determinants is discussed in relation to borehole construction and completion guidelines for contractors and drillers. Journal of Applied Sciences and Environmental Management Vol. 10 (3) 2006: 59-65
Management of Water Supply Reservoirs under Uncertainties in Arid and Urbanized Environments  [PDF]
B. F. Alemaw, E. O. Keaitse, T. R. Chaoka
Journal of Water Resource and Protection (JWARP) , 2016, DOI: 10.4236/jwarp.2016.811080
Abstract: Simulation and evaluation study of the three Water Supply Reservoirs in the Notwane Catchment was undertaken using a hybrid modelling approach linking the reservoir simulation model (HEC-ResSim) model and a reservoir reliability analysis (RRA) model. It was used to understand the management challenges and operation aspects facing the recent failure and declining water supply from three reservoirs in Gaborone and the surrounding areas, a typical arid and urbanized environment where current and future water supply reliability is challenged by both climate and anthropologic factors. The model was analysed for a calibration period of ten years (1993-2002), and verification period of eight years (2003-2010) and then simulation period of 40 years (2011-2050). The simulation period up to the year 2050 was considered to include the year 2035, which is the planning horizon of the National Water Master Plan. The model calibration and verification results are satisfactorily accepted for the fit of the daily water levels. The values of R2 and the Nash-Sutcliffe model efficiency criteria for the calibration period, are 0.81/60%, 0.62/27% and 0.54/39% for the Bokaa dam, Gaborone dam and Nnywane dam, respectively. Various scenarios were considered to determine the plausible sources of uncertainty and challenge for operation and management of the water supply reservoirs considering: population and urbanization, sedimentation, seepage, climate change, operational aspects, among others. From the RRA model, it was found that Gaborone dam, which is the largest of the three dams has lower resilience, lower reliability and higher vulnerability associated with increasing population pressures, urbanisation and climatic factors. Climate change, sedimentation, seepage, operational rules, contributing to the operation and management of the dams could have accelerated the drying up of the reservoirs and the prevailing water supply situation, which might continue to be the future possible challenges of water supply in the area.
Genotype X environment interactions and stability of soybean for grain yield and nutrition quality
F Gurmu, H Mohammed, G Alemaw
African Crop Science Journal , 2009,
Abstract: Soybean Glycine max (L.) Merrill] is the world’s leading source of oil and protein. It has the highest protein content of all food crops and is second only to groundnut in terms of oil content among food legumes. Study on genotype x enviroment interaction (GE) and stability of twenty soybean [Glycine max (L.) Merrill] genotypes was conducted for grain yield, oil and crude protein content at six environments in 2007. The objectives of the experiment were to determine the magnitude of GEI and stability of released and elite soybean genotypes and thereby identify widely and/or specifically adapted genotypes under Ethiopian conditions. There are strong significant (P<0.01) environment, genotype and GEI effects, and environment and GEI captured larger portion of the total sum of squares, which reveals the influence of the two factors in evaluating soybean genotypes and, hence, the need for stability analysis. Three most popular stability parameters were used for stability analysis. Three genotypes that had medium yield performance, IPB-144-81(p), Braxton and Awassa-95, were identified as stable genotypes for grain yield. The three top yielding genotypes, AGS-115-1, TGX-297-6f-1 and AGS-162, were found unstable and can be recommended for narrow adaptation to Gofa, Areka and Inseno, respectively. Haddee-1 and Braxton were genotypes with high oil content and showed stable performance across the environments. TGX-297-6f-1 had high oil content but unstable with specific adaptation to Bonga. Clarck-63k had the highest crude protein content and also very stable one. IPB-144-81(p) and AFGAT had high crude protein content but very unstable and specifically adapted to Areka.
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