Stream Flow Forecasting and Assessment of Reservoir Performance under Changing Climate (Case Study of Halele and Warebessa Reservoirs, Omo-Gibe Basin, Ethiopia)

Abstract

Now a days, change in climate variables caused by natural and anthropogenic effects have posed big problem on many water resource projects in our country. The main aim of this thesis is to assess the impacts of climate change on stream flow and evaluation of reservoir performances using Reliability, Resilience and Vulnerability indices (RRV). Hydrological data (stream flow) and Meteorological data such as precipitation, temperature (Tmax, Tmin) relative humidity and solar radiation in and around the study area used. And a recent Representative Concentration Pathway (RCP) scenario was used for climate change impact evaluation. Climate data (RCP2.6, RCP4.5 and RCP 8.5) were evaluated for the base and future climate scenario which develop (1976-2005), (2021-2050) and (2051-2080). The HEC HMS model was used to simulate the current and future inflow volume to the reservoir. The model performance resulted in NSE = 0.76, R2 =0.78 and D= -3.17 during calibration. During validation, NSE = 0.8 NSE, R2 =0.82 and D= 2.1 was obtained. The projected future climate scenario shows an increasing trend for both maximum and minimum temperature however, for the case precipitation decreasing trend for future scenarios. The average time base reliability of the reservoirs was less than 50% for no reservoir condition and greater than 50% for the other condition considered but volumetric reliability and resilience varies between 50% and 100% for all conditions. According to the vulnerability result the reservoirs will face shortage of flow which ranges from 5.7% to 33.8%. Finally, HEC_ResSim model was used to evaluate reservoir simulation and hydropower generation for different climate scenarios. The output result of HEC_ResSim model was Maximum Average Energy generated for Upper Dam 349.4MWhr and 331.2MWhr for short and long term respectively and average Energy generated for Lower Dam 4045.82 MWhr and 3946.74MWhr for short and long-term future scenario, respectively. Generally for RCP scenarios, Both Tmax and Tmin are increasing where precipitation and inflow to Reservoir is Decreasing Due to increasing of Evapotranspiration. And there is a fluctuation of power generation with seasonal variation for the wet season and dry season energy output and from impact of climate analysis the result shows Variation (either decreasing or increasing) as compared to estimate by EEPPCO.