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COMPARISON OF SWAT AND WEPP FOR MODELING ANNUAL RUNOFF AND SEDIMENT YIELD AND QUANTIFCATION OF NUTRENT LOSS IN AGEWU MARIYAM WATERSHED, NORTHERN ETHIOPIA
(Hawassa University, 2022-10-22) YALELET ABIE WORKU
Unevenly heavy rainstorms during the rainy season create runoff and soil erosion which affects soil fertility and production, especially in northern Ethiopia. In this study soil and water assessment tool (SWAT) and geographic water erosion prediction project (GeoWEPP) were applied to compare estimation of annual runoff and sediment yield and quantification of nutrient loss in Agewu-Maryam watersheds eastern Amhara, region, Ethiopia. To run both models, need spatial and temporal data distribution is required as an input. The soil textures and other selected soil properties were determined in the field and the laboratory and a soil map were derived from the digital soil map of the world. A land-use map was prepared based on manually digitizing from Google earth image. A Digital Elevation Model of the watershed was used for delineating the watershed and preparing a slope map. ArcGIS 10.4 was used for both models for basic interface for further analysis. During each runoff event, runoff samples were collected and the sediment concentrations were analyzed in the laboratory. The simulation result of long-term (24-year) average means annual runoff and sediment yield from WEPP and SWAT models were estimated. The results were performed well as indicated by R 2 0.86 and 0.91 and with NSE 0.54 and 0.71 for monthly runoff were satisfactory for SWAT and WEPP models compared with observed value respectively The estimated average mean annual runoff and sediment yield at the outlet of the watershed was 65.54mm and 146.14mm and 43t/ha/yr and 41.7t/ha/yr respectively for WEPP and SWAT models. The t statics result shows that there is no statistically significant difference with p-value (0.97 for runoff and 0.98 for sediment) between the two models' simulation results. Some of the Sub watershed were identified and prioritized as more susceptible to soil erosion and give more attention first to this area for reducing runoff and soil erosion. The total nutrients loss within the suspended sediment were 33.74kg/ha/yr N,6.79kg/ha/yr P, 642.5 OM kg/ha/yr, and 1.52 K for the watershed. Hence SWAT and WEPP models were well suited for the estimation of annual runoff and sediment yield. The sediment yield simulated from both models was high which was alarming and far beyond the soil loss tolerable rate. Therefore, the result of the model could be used as a decision-making tool
ASSESSING THE IMPACT OF LANDUSE/LAND COVER CHANGE ON STREAM FLOW AND FUTURE PREDICTIONS OF LANDUSE/LAND COVER CHANGES OF BELES SUB-BASIN, UPPER BLUE NILE BASIN, ETHIOPIA
(Hawassa University, 2023-08-22) TSEGA MOGES
Landuse and land cover change drives changes that limit availability of products and services for human, and it can undermine environmental health. Studying impact of landuse/land cover changes on the stream flow is very important for proper basin management. Hence this study investigated the past and potential future land cover changes, and the impact of the past on the stream flow of Beles Sub-Basin using using the Soil Water Assessment Tool (SWAT). To analyze the change that in the study area, satellite images were downloaded for 1987, 2002, and 2019 years and processed using ERDAS Imagine 2014. Then using supervised image classification, the satellite images were classified to agriculture, wetland, forest, shrub land, and urban land. Accuracy assessment was done, and overall accuracy of 86.25%, 88.7% and 87.9%, were achieved for the classified images of 1987, 2002 and 2019 respectively. The net changes of landuse/land cover of the study area from 1987 to 2019 indicated that forest, shrub land and wet land decreased by 4.73%, 10.59%, and 1.10%, respectively, while Agriculture, and Urban, increased by 14.18%, and 2.24%, respectively. The future LULCs of 2035 and 2055 were projected by IDRISI (CA Markov method), and the result indicated an increase of Agriculture 10.94%, Urban 44.04%, where as forest -12.63%, shrub land -11.35%, and wetland -43.61% decreased. Ten parameters identified to be sensitive for the stream flow. Model calibration was carried out using observed stream flow data from (1989-2010) and The validation was performed from (2011-2019). Both results showed good match between measured and simulated stream flow data with R 2 and ENS achieved 0.80, 0.74 for calibration and 0.64, 0.78 for validation respectively. Due to LULCC, the mean annual Stream flow increased by 3.04m3 /s from 1987-2002, and, 2.83m3 /s from 2002-2019 and seasonal flow increased by 12.05m 3 /s, and 5.49m 3 /s in the wet season, while increased and decreased by 2.13m 3 /s and -2.78m 3 /s respectively in the dry season. The surface runoff increased, while groundwater flow decreased from 1987 to 2002 and from the year 2002 to 2019 the mean monthly stream flow increased by 23.29m3 /s for the wet months while for the dry months decreased by 6.31m3 /s. The Stream flow change to different predefined study years indicates LULCC has significant impacts on the stream flow of the study area. To mitigate LULCC, local and national officials in the Beles Sub-Basin should be invited to develop and implement scientific and suitable planning and management plans
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.
MODELING OF SURFACE WATER RESOURCES FOR WATER ALLOCATION: A CASE STUDY IN UPPER GIDABO WATERSHED, GIDABO SUB BASIN, ETHIOPIA
(Hawassa University, 2023-10-28) TAMIRAT SHUKE KITAWA
The processes of population increase, urbanization, industrialization, and dependency ratio has resulted in a rapid demand increase for water resources in the developing world. Water managers in the watershed of the developing world face the increasingly difficult task of allocating the limited water resources among competing users for fulfilling their demands due to difference in available resources and water demand increment. Water resources management has limited in the Upper Gidabo watershed and there is traditional water allocation are vastly practiced. This was due to lack of sufficient awareness about available water resources and management in watersheds. Understanding the potential and use of surface water in upper Gidabo would help to increase the productivity of Agriculture and other sectors, to improve the traditional water management system. Therefore the objective of this study was to Modeling of surface water resources for water allocation under developed scenarios for maximizing overall benefits without compromising ecological requirements in the Upper Gidabo watershed in Gidabo sub basin. To achieve the aim of this study soil and water assessment tool (SWAT) model was used to determine the available surface water resources of the watershed after sensitivity analysis, calibration and validation of the model by SWAT_CUP sufi-2 algorithm. The simulated result revealed that the total average surface water potential from the watershed was 773.5 MCM annually during the study period (2021). Both the calibration and validation result for Aposto and kolla gauging station showed a good performance with a value of R2 and NSE of 0.83 and 0.65 for calibration and 0.81 and 0.6 for validation in Aposto and 0.79 and 0.62 for calibration and 0.78 and 0.61 for validation in Kolla gauging station, respectively. After this Water Evaluation and Planning (WEAP) model was used to assess water demands. To assess irrigation water requirement of the sixteen (16) crop types CROPWAT 8.0 software was used. After assessing the currently existing demands Different scenarios were also developed to determine the future water demand, and unmet demand from overall time period of 2021-2050, This scenarios namely: reference, population growth and increased water demand scenario was established to determine increasing demands under increasing human as well as Livestock population, agricultural areas and different industrial activities. The current (2021) utilization is about 110.4 MCM for consumptive use and non-consumptive (EFR) use, For EFR 10% considered from available flow to maintain ecological functioning and water resource development in the watershed. The current demands fully met with available flows and for scenarios the assessed total annual water demand may be expected to be 126 MCM, 195.1 MCM and 341.8 MCM for the reference, high population growth, and increased water demand scenarios, except increased water demand scenario the other scenarios is met fully, It is appropriate to shape more effective policies and regulations in the area for effective water resources management in reducing water shortage and achieving downstream water needs in the future
QUANTIFYING SURFACE WATER AVAILABILITY AND DEMAND ANALYSIS IN THE POORLY GAUGED CATCHMENTS OF JEMMA SUB-BASIN, ABBAY/UPPER BLUE NILE BASIN, ETHIOPIA
(Hawassa University, 2023-10-28) SAMUEL ABABU FARIS
The socioeconomic activities and environmental changes with respect to the spatiotemporal variation of streamflow in the catchment intricates the supply and demand management system. Assessment of the surface water potential and demand analysis at a sub-basin level was aimed at estimating escalating demands of the catchments and meeting the society's needs without causing potential negative consequences on the ecological balance of the catchments. To quantify the surface water availability of the catchments, the soil and water assessment tool (SWAT) model was used after the sensitive analysis, calibration, and validation of the model was done by SWAT-CUP. The annual total demands was anlysed in water evaluation and palanning (WEAP) model after the surface water potenial was quantified. Different‘’what if” scenario was developed to forecast future water demand, supply requirement, and unmet demands in 2022-2035. The model showed the mean annual flow depth in Beressa and Robigumer catchments was 174.4mm and 166.91mm, respectively and contirbutes to 37MCM and 149.05MCM surface water potential, respectively. From the mean annual precipitation recieved in the Beressa and Robigumer catchments, 48% and 43% was lost through evapotransipiration, respectively. The model performace showed satisfactory result with a value of 0.89(R2 ), 0.87(NS), and 0.76(R2 ), 0.74(NS) in calibration, and 0.71(R2 ), 0.70(NS), and 0.72(R2 ), 0.66(NS) in validation in the Beressa and Robigumer catchments, respectively. The CROPWAT 8.0 model was used to determine the irrigation water requirement of selected crops. The total consumptive water demand in 2022 was 11MCM(29.7%) and 8.1MCM(5.4%) of the total surface water potential of the Beressa and Robigumer catchments, respectively. The total water demand in projected irrigation area scenario was 125.64MCM(84.05%) of the surface water potential of the Robigumer catchment in the year 2035. The EFR was significant parameter to maintain the ecological balance of catchments. In the two last scenarios the total water demand were beyond the surface water potential of the Beressa catchment. To mitigate the future water stress and scarcity in the catcments, dopting rainwater harvesting, other potential sources, and integrated water resources management options are importannt
ASSESSING THE IMPACT OF LANDUSE/LANDCOVER CHANGE ON THE HYDROLOGICAL RESPONSE OF KOLA RIVER WATERSHED, SIDAMA REGION, ETHIOPIA
(Hawassa University, 2021-10-23) NIGUSU MULETA ETANA
Landuse/land cover change is one of the major factors that affect the hydrological response of watersheds. Hence studying the impacts of past and future landuse/land cover changes on the hydrology of Watershed is very important for proper watershed management. This study investigated the past and potential future land cover changes and their impact on the hydrological response of the Kola River Watershed by using the Soil Water Assessment Tool (SWAT).To detect and analyze the change that had taken place in the study area, satellite images were downloaded for 1988, 1998, 2008, and 2018 years and processed using ERDAS Imagine 2014. Then by using the supervised image classification technique, the satellite images were classified to agriculture, agroforestry, built up pasture, land, and forest landuse the land cover types. Then accuracy assessment was done, and overall accuracy of 87.83%, 88.41%, 89.15%, and 91.76%, was achieved for the classified images of 1988, 1998, 2008, and 2018 respectively. The changes of landuse/land cover of the study area from 1988 to2018 indicated that Pastureland, Forest, and Agroforestry decreased by 69.55%, 40.86%, and 15.77%, while Agriculture, and Built-up, increased by 24.67%, and 23.9%, respectively. The future LULC of 2048 was projected by IDRISI (CA-Markov method) and the result indicated a continuous increase of Agriculture and Built-up areas as the other landuse land cover such as forest, pastureland and Agroforestry decreased. Model sensitivity analysis was made to choose the most sensitive parameters. Then, R2 and ENS achieved 0.87, 0.77 during calibration and 0.85, 0.74 for validation respectively. The model performance evaluation indicated that SWAT can be used for modeling the impact of historical and projected LULCC on the hydrological response of the study Watershed. As the investigation of 1988 to2018 shows, due to LULCC, the seasonal flow increased by 25.71%, 23.73%, and 19.96%in the first and, second rainy seasons, and short rainy season, while it decreased by 22.21% in the dry season respectively. The annual surface runoff and water yield increased and by 22.21%, and 3%, whereas evapotranspiration and lateral flow, decreased by, 6.21%, and 14.61% respectively. The future LULCC prediction of 2048 showed thatseasonal flow increased by 29.03%, and 28.08%, 14.6% in the first and second rainy season, and short rainy season and decreased by 19.3 in dry seasons. Generally, the investigation of hydrological response to LULCC by taking other data constantly at different predefined study years indicates LULCC has significant impacts on the hydrological response of the study watershed. Therefore to overcome the impact of LULCC, local and national policymakers should be invited to prepare and apply scientific and appropriate watershed planning and management, strategies in the Kola River Watershed
HYDROLOGICAL RESPONSE OF CLIMATE CHANGE ON WEYB RIVER WATERSHEDS: THE CASE OF BALE MOUNTAINOUS AREA, ETHIOPIA
(Hawassa University, 2019-04-18) NESHA BAHMUD USHI
The hydrological regimes and cycles within a certain watershed can be changed by the global climate variability and change. This change adversely impacts on environmental sustainability,water resources, agriculture and ecosystems. The current study investigates the hydrological impacts of climate change in essence, changes in precipitation and temperature over the Weyb river watershed. It is based on a sample of Coupled Model Inter comparison Project version 5 (CMIP5) downscaled over the Africa-Coordinated Regional climate Downscaling Experiment (CORDEX) domain by a Rossby Centre regional atmospheric model version 4 (RCA4) output, under RCP 4.5 and RCP 8.5 scenarios. Variance scaling and linear transformation bias correction methods was used to develop the simulation output of RCA4 regional climate model with high correlation to the observed data. ArcSWATmodel was used to generate future water availability in the basin. The bias corrected data were then used as input to the SWAT model to simulate the corresponding future flow regime in Weyb river watershed which is calibrated daily at R2 = 0.6,ENS = 0.5, and validated daily at R2 =0.58,ENS 0.57. The future projections are made for three time periods; 2020 (2010-2039),2050 (2040-2069) and 2080 (2070-2099). Results revealed that future predicted both temperatures, and precipitation revealed a statistically significant (at 5% significant level) increasing trend in the forthcoming periods as perceived by MannKendall test.Trend analysis with test using Mann Kendall (MK) and Sen's slope non-parametric test was applied to detect significant trends on the climate parameters and stream flow for future periods using XLStat software. The level of statistically significant trend was selected at α = 0.01,α = 0.05andα = 0.1level of significance. The annual mean daily stream flow revealed an increase, possibly, in the ranges 9.16-23.39% (RCP8.5), and 3.97-20.30% (RCP4.5). The result revealed that the maximum and minimum temperatures increase for all the two scenarios in all future time horizons. Rainfall change for all the two RCPs scenarios were variable. Results also revealed that a decrease of stream flow in all months on the dry season this might cause water shortage in the lowland region, and greater increase of stream flow in an intermediate and rainy seasons this might cause flooding to some flood prone region of the basin. A significant conclusion from the study is that changes in rainfall have larger effects on stream flow.The use of integrated hydrological modeling in impact assessment and the inclusion of other factors that cause imbalance in the stream flow should be enhanced in the Weyb watershed
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
IMPACT OF CLIMATE CHANGE ON SURFACE WATER RESOURCE AVAILABILITY: A CASE STUDY IN WELMEL WATERSHED,GANALE-DAWA BASIN, SOUTH ETHIOPIA
(Hawassa University, 2018-10-27) BERECHA DINSA CHAKA
Climate change, nowadays, has significant impact on the water resource system of an area. This study was conducted for Welmel watershed, Ganale-Dawa river basin, Ethiopia, using Soil and Water Analysis Tool(SWAT) hydrological model and General Circulation Model (GCM) aiming at estimating the impact of climate change on water availability of the study area. By making proper calibration, precipitation and temperature outputs of HadCM3 coupled atmosphere-ocean GCM model for A2a (medium to high) and B2a (Medium to low) SRES emission scenarios were downscaled using the Statistical Downscaling Model (SDSM). The downscaled minimum temperature shows an increasing trend in all future time horizons for both A2 and B2 scenarios. The average annual minimum temperature will be 0.30 C change from baseline in 2020s (2014-2041).In2050s (2042-2069) of minimum temperature will be 0.65o C and also 0.63o C for A2 and B 2 scenario respectively. For the 2080s (2070-2099) periods the average annual minimum temperature will be increased by 1.3o C and 1.03o C for A2 and B2 scenario respectively. The downscaled maximum temperature scenario, on the other hand indicates that for most months there will be an increasing trend for both A2 and B2 scenario. The projected temperature in 2020s indicates that maximum temperature will rise by 0.232o C. In 2050s the increment will be 0.527o C and 0.53o C for A2 and B2 scenario respectively. The future precipitation of the study area is expected to annual average increase by 11.90% for A2a and 11.67% for B2aemission scenarios. The actual evapotranspiration will also increase by 3.64% for A2a and 3.75% for B2a respectively. The results obtained from this investigation indicate that there is significant variation in the seasonal and monthly flow. In the main rainy season (June-September) the runoff will be reduced by 12% in the 2080s. The result from synthetic (incremental) scenario also indicates that the catchment is sensitive to climate change. As much as 23% of the seasonal and annual runoff will be reduced if an increment of 2o C in temperature.
ASSESSING THE IMPACTS OF CLIMATE CHANGE ON STREAMFLOW UNDER CMIP6 CLIMATE PROJECTION IN THE UPPER OMO GIBE RIVER BASIN, ETHIOPIA
(Hawassa University, 2023-03-25) LEMLEM GETNET MOLA
Climate Change is projected to have an impact on future streamflow in various watersheds. This study examined the impacts of climate change on streamflow in the Upper Omo River Basin using a Soil and Water Analysis Tool (SWAT). Projected climate variables (precipitation and temperature) ensemble of 5 Global Circulation Models (GCMs) were obtained from the World Climate Research Programme (WCRP), downscaled by the SDSM4.2 model and applied under the Shared Socioeconomic concentration pathways (SSP2-4.5) and (SSP5-8.5) scenarios. The downscaled SSPs data cannot be directly used to the hydrological model (SWAT) to simulate flow so, Distribution Mapping bias correction method was selected for this study. SWAT was calibrated and validated before it was used for simulation purpose. The performance measures R2 and NSE for calibration (2000-2013) and validation (2014-2019) were 0.79 and 0.71 and 0.86 and 0.85 respectively. Mann Kendall (MK) trend testing was used to determine if a change is statistically significant and to detect trends in temperature and precipitation. According to RCP4.5 and RCP8.5, the emission scenarios predicted significant increasing temperature, but significant decreasing precipitation. Streamflow was simulated for two consecutive periods from 2020 to 2045 and from 2046 to 2071 for both scenarios and compared with the base period from 2000 to 2019 to explore the impact of climate change on Streamflow. The results indicated that the basin is likely to experience increased temperatures and altered precipitation patterns, whereas overall annual flow was projected to be significantly decreasing under SSP2-4.5 and SSP5- 8.5 emission scenarios in the mid and near future. These changes are likely to have major implications for water resources management in the region, particularly for agriculture, hydropower generation, and ecosystem services. The findings suggest the need for adaptive measures to address these impacts, including improved water management strategies and increased investment in climate-resilient infrastructure.

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