ASSESSMENT OF CLIMATE CHANGE IMPACT ON INFLOWS TO KOKA RESERVOIR IN UPPER AWASH SUB BASIN
Creators: name: SALIH DURI ABDULAHI
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2019
Subjects: HBV RCM Climate model Bias correction Climate Change Discharge

description: Climate change impact and its variability on stream flows are now becoming one of<br> the significant challenges. Hence evaluation of the impact and the trends of the change<br> is very important at watershed level. The aim of this study was to evaluate the impacts<br> of climate change on inflows to Koka reservoir in upper awash sub basin using HBV<br> model. The climate model variables (precipitation and temperature) were obtained<br> from Coordinated Regional Downscaling Experiment (CORDEX) from Regional<br> Atmospheric Climate Model Version2.2 (RACMO22T) under representative<br> concentration pathway (RCP4.5) and (RCP8.5) scenarios. Bias correction was applied<br> to climate variables before transferred to hydrological model (HBV) to simulate<br> discharge. For model performance evaluation; Coefficient of determination (R2), Nash<br> Sutcliffe Efficiency (NSE) and percent bias (PBIAS) were used during calibration (2002-<br> 2010) and validated (2011-2015) period. The result of calibration and validation (R2,<br> NSE and PBIAS) are 0.88, 0.78 and -6.72 and 0.88, 0.83 and -12.51 respectively. Stream<br> flow was simulated for two consecutive periods (2021–2040) and (2041–2060) for both<br> scenarios and compared with the base period (1996–2015) to explore impact of climate<br> change on inflows. The result obtained shows that overall mean annual flow is projected<br> to decrease by 11.7 and 18.1% under RCP4.5 and RCP8.5 scenarios respectively. For<br> the period (2021-2040) flow expected increase in October under both scenarios. The<br> increment will be 113.2% and 115.5% under RCP4.5 and RCP8.5 respectively while the<br> maximum reduction will be expected in March (84.6%) under RCP4.5 and in January<br> (69.5%) under RCP8.5. Similarly for the period of (2041-2060) the maximum increment<br> will be in October under both scenarios while the maximum reduction projected in<br> January under both scenarios. Flow duration curves indicate that, the probability of<br> occurrence of high flow (Q5) and median flow (Q50) are likely to be more in the future<br> under both scenarios. However, low flow (Q95) is predicted to decrease under both<br> scenarios. High flow (Q5) will be vary from (35.6% to 55.9%) and median flow (Q50) vary<br> from (37.2% to 85.8%). Low flow (Q95) expected to decrease by 78.3% under RCP4.5<br> and 71.8% under RCP8.5. The monthly and seasonal variations are expected to be<br> more relative to annual variations. During summer and autumn season, flow expected<br> to increase while decrease in winter and spring in the study area under both scenarios.<br> As the result of high increment in flow in certain months and high reduction in the<br> other months, flood and drought may be expected in future in the basin. Overall there<br> will be a variations of flow month to month and season to season. Therefore, it is<br> important to consider this variation of flows to Koka reservoir to frame appropriate<br> guidelines for planning and management<br>