Water Resource

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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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    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.