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    STREAMFLOW RESPONSE TO CLIMATE CHANGE ON TIKUR WUHA SUB WATERSHED, RIFT VALLEY BASIN, ETHIOPIA
    (Hawassa University, 2018-10-23) BROOK LEGESE DADHI
    Climate changes alter regional hydrologic conditions and results in a variety of impacts on water resource systems. Such hydrologic changes will affect almost every aspect of human well-being. Simulation models of watershed hydrology and water quality are extensively used for water resources planning and management. This study aims to assess the streamflow response to Climate Change on Tikur Wuha Sub-watershed, Rift Valley Basin of Ethiopia. In the study the daily hydro-meteorological data values for the baseline period of 1981-2005 were used. Historical Representative Concentration Pathway (RCP) data along with observed data of precipitation and temperature were used for extraction and bias correction using CMhyd tool. After evaluation of bias correction methods using residual plot, and RMSE, MAE and RE, the downscaled climate data such as, RCP4.5 and RCP8.5 scenarios was used for the future period assessment. Soil Water Assessment Tool (SWAT) models were used to assess the streamflow response to Climate Change. Calibration and validation of the model output were performed by comparing simulated streamflow with corresponding measurements from the Tikur Wuha outlet for the periods of 1992-2001 for calibration and 2002-2005 for validation using SWAT-CUP(SUFI-2). The model calibration and validation results shows a good agreement with the observed flow with the coefficient of determination 0.79 and 0.86, and a Nash Sutcliffe efficiency was 0.56 and 0.64, respectively. The result of projected temperature reveals a systematic increase in all future time periods for both RCP 4.5 and RCP 8.5 scenarios, and for all considered period whereas the projected result of precipitation was inconsistent throughout all future time periods and for both RCP 4.5 and RCP 8.5 scenarios. The dynamically downscaled daily climate variables (precipitation and temperature) were used to simulate future projections of streamflow. Streamflow projections for future time periods showed that mean annual streamflow may increase by 15.43, 23.48, and 25.42% in 2020s, 2050s, and 2080s, respectively, from the baseline period for RCP 4.5 scenario, whereas for RCP 8.5 scenario, it will be expected to increase by 29.58, 34.20, and 38.72% in 2020s, 2050s, and 2080s, respectively. The model simulations considered only future climate change scenarios assuming all spatial data constant. Therefore, future study need to consider impact of land use/cover change on the sub-watershed for future sustainable development plan.
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    IMPACT OF CLIMATE CHANGE ON THE GROUNDWATER HYDROLOGY OF LAKE ZIWAY WATERSHED, ETHIOPIA
    (Hawassa University, 2022-10-23) MIERAF ABEBE DONKA
    Climate change poses uncertainties to the supply and management of water resources. The relationship between the changing climate variables and groundwater is more complicated and poorly understood. Groundwater resources are related to climate change through the direct interaction with surface water resources, such as lakes and rivers, and indirectly through the recharge process. The impact may be worse for developing countries like Ethiopia because of their economies are strongly dependent on basic forms of natural resources. This thesis presents the likely impact of climate change on groundwater hydrology of Lake ziway watershed located in the Rift Valley basin of Ethiopia, The RCP scenarios of types 4.5, and 8.5 were used for the climate projection from the CORDEX Africa domain from CMIP5. The RCM of RCA4 was used to generate future possible local meteorological variables in the study area. These data were used as input to the Soil and Water Assessment Tool (SWAT) model to simulate the corresponding future streamflow Variability in the Ziway watershed. SWAT-CUP, a program for calibration and uncertainty was utilized for uncertainty analysis. The two projected time periods for this study were the 2040s, and 2070s. In the Lake Ziway watershed, there exists a climate change in the study period of 1989-2019. Since, there is a significant change from the base period to the projected time periods, therefore there would exist a climate change impact for the projected time periods under both scenarios in the Lake Ziway watershed. Therefore, climate change shows a significant decreasing impact on the groundwater flow of Lake Ziway watershed, which in turn affects the level of Lake Ziway significantly
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    WATER RESOURCE POTENTIAL INVESTIGATION OF LAKE HAWASSA WATERSHED BY USING A SOIL AND WATER ASSESSMENT TOOL (SWAT
    (Hawassa University, 2019-07-24) JUNDI YUSUF ABRAHIM
    Uncertainties in information about fresh water resource potential have created a critical situation for many countries. Investigating spatiotemporal variability of water resources is, therefore, a critical initial step for water-resource management. Successful planning and management of water resources require the application of effective integrated water resources management (IWRM) models that can solve the encountering complex problems in these multi-disciplinary investigations. In this work, the water resources of Lake Hawassa watersheds were modeled using the Soil and Water Assessment Tool (SWAT), which is a continuous-time, semi-distributed, process-based model. The SWAT-CUP program was used for calibration/validation of the model with uncertainty analysis using the SUFI-2 (Sequential Uncertainty Fitting program) algorithm over the period of 1990- 2015 at one gauge station. Parameter transfer method was used from gauged (Tikurwuha) sub catchment to ungauged one. The performance of the SWAT model was evaluated through sensitivity analysis, calibration, and validation. Ten flow parameters were identified to be sensitive for the stream flow of the study area and used for model calibration. The model calibration was carried out using observed stream flow data from 1995 to 2010 and a validation period from 2011 to 2015 years. Both the calibration and validation results showed satisfactory match between measured and simulated stream flow data with the coefficient of determination (R2 ) of 0.71 and Nash-Sutcliffe efficiency (NSE) of 0.66 for the calibration, and R2 of 0.64 and NSE of 0.59 of the validation period. The results reveal that the annual blue-water potential (water yield and deep aquifer recharge) of Lake Hawassa Watershed is 854 million m3 , Whereas the green-water flow (actual evapotranspiration) (ET) is 629 million m3 and green water storage (soil moisture) is 82 million m3 . Watersheds located around Wondo-Genet yield more blue-water resources compared to watersheds at the western side. The model highlights the water potential of the catchment under current circumstances and gives an insight into its spatiotemporal distribution over the watershed. This study provides a strong basis for the forthcoming studies concerning better water-resources management practices, climate change, and water-quality studies, as well as other socio-economic scenario analyses in the region.
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    ASSESSMENT OF CLIMATE CHANGE IMPACT ON SURFACE WATER RESOURCE IN WOSHA WATERSHED, RIFT VALLEY LAKES BASIN, ETHIOPIA
    (Hawassa University, 2024-10-16) ELSAE WARE GIDESA
    Climate change (CC) and Land Use/Land Cover (LULC) changes present significant threats to global water resources and socio-economic systems. This study aimed to evaluate the impact of climate change and LULC changes on the availability of surface water resources in the Wosha watershed, located in the Rift Valley Lakes Basin (RVLB) of Ethiopia. The available water resources were assessed using the Soil and Water Assessment Tool (SWAT), a semi-distributed, physically-based hydrological model. Calibration and validation of computed stream flow were conducted using SWAT-CUP with the SUFI-2 algorithm. Bias-corrected data from three climate models output from Coupled Model Intercomparison Project Phase 6 (CMIP6) models such as CANESM5, MIROC6, and NESM3 were used to assess baseline (1985-2014), mid-term (2041- 2070), and long-term (2071-2100) periods under the Shared Socioeconomic Pathways (SSP2 4.5 and SSP5 8.5) climate scenarios. The SWAT model's performance was robust, achieving R² values of 0.88 and NSE values of 0.75 during calibration, and R² values of 0.83 and NSE values of 0.72 during validation for monthly simulations. The projections indicate that both rainfall and temperature will increase under SSP2 4.5 and SSP5 8.5 scenarios in the mid-term period, with a temperature rise of 1.2°C expected under SSP5 8.5. Precipitation is also expected to increase by 1% to 10% in the long term for both scenarios. Therefore, the primary objective of this study was to assess the impact of climate and LULC changes on the availability of surface water resources in the Wosha watershed. The results underscore the importance of understanding surface water availability and mitigating the impact of climate change to ensure future water resources for the region.
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    ANALYSIS AND CHARACTERIZATION OF HYDROLOGICAL DROUGHT UNDER CLIMATE CHANGE IN HAMASSA WATERSHED, RIFT VALLEY BASIN
    (Hawassa University, 2024-07-20) REDIAT LEGESE SIME
    Hydrological drought occurs when there is an extended period of significantly reduced water availability, leading to depleted water sources and severe impacts on ecosystem and communities. Water scarcity caused by prolonged periods of reduced rainfall due to climate change can lead to the natural disaster of drought. However, little has been done so far on hydrological drought under climate change in Hamassa watershed. This study aimed to analyze and characterize hydrological drought under climate change in the Hamassa watershed, Rift Valley Basin, Ethiopia. Hydrological data (1992-2015), meteorological data (1992-2022), future climate data 2030-2090), spatial data, DEM, land use land cover, and soil were collected. CMhyd software package was used for bias correction of the climate data. The hydrological model soil and water assessment tool (SWAT) was used for hydrological analysis. The simulation result was calibrated and validated using the SWAT calibration uncertainty procedure (SWAT-CUP). Standard precipitation index (SPI) and stream flow drought index (SDI) are used to decide drought conditions in a watershed and to identify drought-prone areas in the watershed. Temperature projections for both the near and long term indicate an increase compared to the current period under both RCP2.6 and RCP8.5 scenarios. Meanwhile, precipitation projections suggest a decrease for the periods 2040-2060 and 2061-2072 under both RCP2.6 and RCP8.5 scenarios. The standard precipitation index (SPI) and stream flow drought index (SDI) results showed that the watershed experiences mild (-0.5- -0.999), moderate (-1- -1.49), severe (-1.5- -1.99), and extreme (≤ - 2) drought events. Droughts are projected to occur in the periods 2040-2060 and 2061-2072 under both RCP2.6 and RCP8.5 scenarios. Sub-watersheds 7, 8, 9, 10, and 11 showed high vulnerability to severe and extreme drought. Drought-mitigating structures are needed to mitigate drought in the watershed
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    ASSESSMENT OF CLIMATE CHANGE IMPACT ON STREAM FLOW OF GIDABO SUBBASIN, RIFT VALLEY BASIN, ETHIOPI
    (Hawassa University, 2022-08-10) YIDIDYA TSEGAYE ALEMU
    Climate changes alter regional hydrologic conditions and result in a variety of impacts on water resource systems. Such hydrologic changes will affect almost every aspect of human well-being. The goal of this thesis is to assess the impact of climate change on the hydrology of Gidabo subbasin located in the Rift Valley basin of Ethiopia. The RCP scenarios of types 2.6, 4.5, and 8.5 were used for the climate projection from the CORDEX Africa domain from CMIP5. The RCM of RCA4 was used to generate future possible local meteorological variables in the study area. These data were used as input to the Soil and Water Assessment Tool (SWAT) model to simulate the corresponding future streamflow Variability in the Gidabo subbasin. SWAT-CUP, a program for calibration and uncertainty was utilized for uncertainty analysis. The three projected time periods for this study were the 2040s, 2060s, and 2090s. The time series generated by RCM of RCA4 driven by MIROC5 indicate a significant increasing trend in maximum and minimum temperature values and a decreasing trend in precipitation for all RCP emission scenarios in Measso station for all time periods. The hydrologic impact analysis made with the downscaled temperature and precipitation time series indicates variation in an increasing and decreasing trend for the three RCP scenarios at different periods respectively. The model output shows that there may be a mean annual, seasonal, and mean monthly decrease in stream flow volume for all RCP scenarios in the Projected time periods in the future. It also shows most of the projections are within the uncertainty bandwidth of 95PPU