Water Resource

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End date: 2019Subject: search.filters.subject.SWAT

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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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    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
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    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.
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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 SURFACE IRRIGATION POTENTIAL: THE CASE OF GIDABO WATERSHED, RIFT VALLEY LAKES BASIN, ETHIOPIA
    (Hawassa University, 2019-03-07) AZEMERAW ALEMU
    Ethiopia has immense potential in expanding irrigated agriculture. Irrigable land assessment is essential for the development of irrigated agriculture. The study was aimed at assessing land potential of Gidado watershed. Land suitable for irrigation development was determined with a GIS-based multi-criteria evaluation, which considers the interaction of various factors such as slope, soil, LULC, proximity to river and road. The Analytical Hierarchal Process (AHP) and ArcSWAT were used for analyzing the different factors by assigning weights and mapping of suitable potential irrigable areas and surface water potential of the study area was estimated using SWAT model respectively. The model was calibrated and validated from observed stream flow data at three monitoring sites within the watershed using the periods of 1993-2004 and 2005-2012 respectively by using SWAT-CUP program and Global Sensitivity Analysis (GSA) was used for identifying important model parameters. The irrigable land of the area was identified using weighted overlay analysis of the suitability parameters, thus the result indicated that 1138.31 km2 areas was classified suitable and 2042.19 km2 area was classified as not suitable for surface irrigation. During calibration and validation, the results of model performance indicators were in the acceptable range (R 2= 0.68, 0.73, 0.72), (NSE = 0.60, 0.63, 0.71) and (PBIAS=12.2, -9.0 and -14.0) for Gidabo, Kola and Bedessa rivers respectively which indicated that a good to very good agreement between observed and simulated values. And average surface water resource potential of the catchment estimated to be 86.36m3 /s or 223.86 MCM. However after analyzing 25 years river discharge and determined the water demand of the crop, 74390.89ha (23.39%) of the potential irrigable area was estimated and could be irrigated consistently with runoff from the river systems. For sustainable irrigation development, other suitability factors such as soil chemical properties, socio-economic, environmental issues, and distance from markets and town should be considered