Browsing by Author "Seid, Jemal"

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    Simulation of Crop Yields in the Amhara Region using a Large area Crop Model as Driven by output from Regcm-4
    (Addis Ababa University, 2012-06) Seid, Jemal; Mengistu, Gizaw (PhD)
    The livelihood of people in many regions of Ethiopia depends on rainfed agriculture. Accurate prediction of crop yield could greatly improve potential famine and allow advanced planning of intervention operations. This thesis explores the feasibility of a combined Regional Climate Model (RegCM) and crop model for crop yield forecasting in Ethiopia, using wheat yield for the Amhara region as a case study. An important focus in the investigation is to validate and asses the ability of RegCM-4 regional climate model to represent the Ethiopian summer rainfall. The ability of the RegCM-4 model in capturing temporal and spatial variability of precipitation over the region of interest is evaluated using metrics spanning a wide range of temporal and spatial (Ethiopian domain average to local) scales against Global Precipitation Climatology Project (GPCP) observational datasets. The simulated period is 1995-2008. RegCM-4 shows a general overestimation of precipitation except the highlands part of the country. The precipitation bias over the Ethiopian highland, our main area of interest, is mostly less than 20%. The model captures well the observed interannual and inter-seasonal variability. On short time scales, simulated daily temperature and precipitation show a high correlation with observations, with a correlation coefficient of 0.79 for kiremit season. It is therefore that RegCM-4 has sufficiently good quality to perform climate change experiments over Ethiopia, for application to impact and adaptation studies. RegCM-4 outputs are used to drive a process-based crop model, General Large Area Model for Annaula Crop (GLAM) for hindcasting zonal wheat yields in the Amhara region. Simulated crop Radiation Use Efficiency (RUE) has been founded to be 1.81 which is expected for C3 crops. The yield in these simulations showed a negative bias (159-200kg/ha) with observed yield over Souther(North Shew Zone) and South Western(Awi Zone) of Amhara regional state. This is probably because at the field level the yield variability was mainly affected by field managements and diseases, pests and so on. GLAM does not predict the effect of the detailed field management, diseases and pests on yield variability; and also in this region there is overestimation of RegCM-4 precipitation, which might have lead to water stress in GLAM model. At regional level(for all grid cells), there were higher correlations (0.74) between observed and simulated yield. We therefore conclude that the GLAM model is suitable to simulate crop yield at regional scale (approximately 50 km) using RegCM-4 outputs
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    Two-Dimensional Conservative Contaminant Transport Modeling of the Akaki Wellfield
    (Addis Ababa University, 2009-11) Seid, Jemal; Worku, Teshome (Mr)
    This thesis work focuses on non-reactive solute transport modeling of the akaki wellfield for two selected groundwater contaminants (chloride & fluoride) for the 25 operating boreholes administered by Addis Ababa Water & Sewerage Authority (AAWSA). The work is conducted based on laboratory analysis of groundwater samples from selected boreholes and based on historical data of the wellfield boreholes. The widespread use of chemical products, coupled with the disposal of large volumes of waste materials, poses the potential for widely distributed groundwater contamination. Because such contaminations can pose a serious threat to public health, prediction of the degree of contamination by appropriate numerical modeling tools is vital to aware the end user from possible risks. Mathematical models solved numerically are the subject of this thesis work focusing on conservative solute transport in the Akaki well field. Chloride & fluoride ions predictive modeling of the wellfield for the next ten years (2007-2017) is made first by calibrating the model input parameters using the available historical solute concentration data for selected boreholes at various periods. For calibration purpose, initial solute concentration was taken as 3 mg/l for chloride and 0.51 mg/l for fluoride and MATLAB simulation of chloride & fluoride ion concentration is done. The simulation results show that while chloride concentrations in the wellfield get increased; fluoride, however, is getting decreasing through out all of the boreholes in the wellfield. This is in agreement with the actual observed pattern of solute load of the wellfield revealing chloride is being introduced in to the wellfield by one or more mechanisms somewhere in the vicinity of the akaki river catchment (ARC) while fluoride is not. Keywords: aquifers, breakthrough curves, initial conditions, boundary conditions, calibration, prediction, conservative contaminant transport, hydraulic conductivity, porosity.