Water Resource

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    ASSESSMENT OF CLIMATE CHANGE IMPACT ON THE WATER BALANCE OF LAKE HAWASSA WATERSHED
    (Hawassa University, 2023-07-25) KIFLE KARITE ONGOCHO
    Assessing the climatic change impact on the water balance of a watershed is vital to develop sound management plans in current and future periods. The main objective of this study was assessing the climatic change impact on the water balance of Lake Hawassa watershed. The study was focused on the projection of climate variables, assessing the historical and future water balance components, and also evaluating the impacts of climate change on the stream flows of Lake Hawassa watersde. The Soil and water Assessment Tool (SWAT) mode was used for assessing the water balance components and to evaluate the climate change impact on the stream flows of Lake Hawassa catchment. SDSM (statistical downscaling model) was used under General circulation model set up for climate modeling. The water balance components of the watershed were computed in gauged and unguaged catchments. According to the SWAT model result in the gauged catchment, the historical average annual precipitation, surface runoff and the evapotranspiration (ET) were 1068.3mm, 155.11mm and 688.3mm respectively. In 2080 for RCP 8.5 the average annual precipitation, Surface runoff and ET will be 972.15mm, 143.17mm, and 812.19mm respectively. The climate change impact on the water balance components of Lake Hawassa watershed was evaluated for RCPs 2.6, 4.5 & 8.5 emission scenarios in the three time periods (i.e. 2020 (2022- 2040), 2050(2041-2070) and 2080(2071-2099). The result from climate model showed a general increasing trend for maximum and minimum temperatures and decreasing trend for precipitation in all the three time periods for all the three emission scenarios. The impact of climate change on the seasonal stream flows of the watershed will generally increases in the Kiremt season in 2020 and 2050 for all scenarios but decreases in Bega and Belg seasons for all time period in all RCPs. The future annual precipitation, Surface runoff, lateral flow, shallow groundwater recharge and water yield will be decreased up to 9 % and 9.9 % respectively and the increase in ET may reach up to 22% at the end of 2099 for RCP_8.5. Due to climate change the future water availability will be reduced in Lake Hawassa watershed. Therefore, the design and implementation of appropriate adaptation and mitigation strategies to the watershed by the decision makers may reduce the adverse effect of climate change.
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    MODELING WATER RESOURCES USING WEAP MODEL FOR EFFECTIVE WATER MANAGEMENT: A CASE STUDY IN LEGEDARA RIVER CATCHMENT, SNNPR, ETHIOPIA
    (Hawassa University, 2017-10-27) HENOK MEKONNEN ARAGAW
    Water is the life blood of all living things yet its availability and management is not well understood and quantified at the catchments scale. Legedara River catchment water resources availability is not well known since the catchment is ungauged and also the water demands within the catchment is not quantified and properly allocated. This study attempted to model the water resources of Legedara river catchment in SNNPR for effective water management through scenario analysis using WEAP model.Hydro-meteorological, spatial, and water demand data were the basic inputs to the model. FAO-Rainfall-Runoff (Simplified Coefficient) method was used to estimate runoff of Legedara River catchment by transferring calibrated model parameters from gaugedWaleme River catchment. However, before transferring calibrated model parameters different procedures were done, since selection of representative catchment, modeling of gauged catchment and calibration and validation. Catchments areal rainfall and reference evapotranspiration are estimated by Thiessen Polygon method and Penman Monteithmethod respectively. Domestic, industrial and environmental water requirements were estimated using WEAP model. Current situation of water demands for the selected water users were simulated. Five different scenarios for future water demands were developed and in addition to these climate scenario was developed and evaluated. During the model setup, all demand sites were assigned equal priority. As a result of parameter derivation hydro meteorological Waleme River catchment is almost similar to Legedara River catchment. The model calibration and validation results were found satisfactory for the gauged catchment (ENS = 0.81; R2 = 0.86 and RVE = -2.64% for calibration and (ENS = 0.77; R2 = 0.81 and RVE = - 7.73% for validation). The water balance components of Legedara River catchment were estimated and mean annual values of rainfall and reference evapotranspiration found to be 1316.42mm and 1142.07mm, while the actual evapotranspiration and runoff constitutes; 538.78mm and 778.65mm respectively. The modeling result revealed that, all the selected demand sites satisfied fully in the current situation and for reference scenario, scenario one, two and four, even though the remaining river flows for the months of December, January and February were almost zero after deduction. However, the result of catchment water resources and demands showed that at the last year of scenario three (2040), there will be a 26.71MCM, i.e., 36.17%, reduction in the total annual flow of Legedara river catchment.Moreover, it was found in the catchment that it is having unmet demands in scenario three. Nonetheless, it was shown that environmental flow requirement of 14.77MCM will be fully delivered at the outlet of Legedara River catchment. Hence, no absolute scarcity of water would develop. In scenario five, the simulating value showed that, increase and decrease of current mean monthly rainfall values by 10% and 5% have an impact on increase or decrease of catchment runoff.Further researches on groundwater availability were also suggested to meet the unmet demands
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    HYDROLOGICAL RESPONSES TO CURRENT AND PROJECTED LAND-USE/LAND COVER CHANGES OF THE WELMEL RIVER WATERSHED, GENALE DAWA BASIN, ETHIOPIA
    (Hawassa University, 2021-03-27) SOLOMON ESHETE AYALEW
    Land use/land cover change is one of the important concerns in many regions of the world. It is recognized that dramatic LULC change can significantly impact regional climate, ecosystem stability, water balance, stream silt up, socioeconomic practices, and biodiversity. The main objective of this study was to assess the hydrological responses to historical and future Land Use/Land Cover Change at basin and sub-basin levels of the Welmel River watershed, which is located in the Genale-Dawa Basin South Eastern Ethiopia using hydrological SWAT model. The study analyses the historical LULC change between the years 1990, 2005 and 2020 and the future year of 2035 and 2050. The hydrological responses to LULC changes in the Watershed were analyzed using the historical and future LULC maps. Images were processed using ERDAS Imagine 2014 and CA-Markov chain model was used for the prediction of the LULC map of 2035 and 2050. Discharge data from 1990 to 2006 and 2007 to 2014 were used for calibration and validation respectively with three years of warm-up period and climate data from 1990 to 2020 time period. The main finding of this study revealed that the coverage of agriculture/settlement increased by a rate of change of 6.85km2 /year, while forestland was declined by the rate of change of 9.16km2 /year over the last 31 years between 1990 and 2020. In the coming 31 years (by 2050), if the current trend of LULC change continues, agriculture/settlement land is expected to increase by the rate of change of 6.73km2 /year, while forestland is expected to diminish by a rate of change of 8.78km2 /year. As a result of LULC change, surface runoff has increased by 25.32% while lateral flow, groundwater flow, water yield, evapotranspiration and percolation declined by 19.91%, 17.17%, 2.38%, 0.36% and 17.17% respectively between 1990 and 2020. If the current rates of LULC change continue, surface runoff is expected to increase by a relative change of 18.47% while lateral flow, groundwater flow, water yield, evapotranspiration and percolation are expected to decline by 26.84%, 17.51%, 2.09%, 1.91% and 17.47% respectively by 2050. Average annually, surface runoff in all 29 sub-basins has increased by 39.90mm and groundwater flow decreased by 34.57mm. The average annual stream flow increased with a relative change of 6.18% from 1990 to 2020 and is expected to increase by 12.69% by 2050. The average wet annual flow from 1990 to 2020 increased by 10.21%, while the average dry annual flow decreased by 6.34%. The average wet and dry annual stream flow is expected to increase and decline by 19.67 % and 6.86% respectively in 2050. Therefore, the Woredas in and around the Welmel River Watershed and the Bale Mountains National Park should integrate to design and implement a proper strategy for protecting and managing the existing forest and woodlands in addition to rehabilitating the degraded areas to maintain the hydrological balance of the watershed.
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    ASSESSMENT OF WATER BALANCES USING SWAT MODEL AND AGRICULTURAL WATER DEMAND ANALYSIS OF GIDABO RIVER CATCHMENT, RIFT VALLEY BASIN, ETHIOPIA
    (Hawassa University, 2020-07-18) CHALA TADESSE
    To use water resources sustainably, it is important to understand the quantity of water resource spatially and temporally. The work presented here attempts to model water balance of one of Gidabo sub-watershed of Ethiopian Rift Valley Basin using the Soil and Water Assessment Tool (SWAT. Statistical model performance measures, the coefficient of determination (R2 ) and Nash-Sutcliffe Efficiency (NSE) were used to evaluate the correlation between the observed and simulated monthly stream flow. The result shows an acceptable performance of SWAT model in simulating the watershed hydrology as evidenced by the NSE value of 0.79 and R2 value of 0.80 at calibration (using data from1990-2009) and NSE = 0.71 and R2 =0.82 at validation (using data from2010- 2014). In terms of water balance components, the long-term annual precipitation is found to be in the magnitude of 1435.58 mm; whereas the surface runoff; total water yield; and actual evapotranspiration, are estimated as 62.20; 1189.73, and 228.40 mm respectively. In order to link the water balance estimation with the local agricultural water demand, wheat and potato are selected for they are common crops for irrigation in the watershed. While taking the month of March, which is the month of maximum agricultural water demand (11.6 m 3 /s), the watershed is found to be water-surplus as indicated by the water availability of the critical month (12.22 m3 /s) to be higher than the demand. This research implies that the use of models in supporting decisions related to water resources development and management is paramount important to understand how the system functions