Estimation of Sediment Yield under the Impact of Climate Change (Case of Mille River Watershed, Lower Awash Sub-Basin, Ethiopia)
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Date
2022-03
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Addis Ababa University
Abstract
Climate change impact and its variability on stream flows and sediment yield are now becoming one of the significant challenges. Hence evaluation of the impact and the trends of the climate change on hydrological process is very important at watershed level. The aim of this study was to assess the impact of climate change on the sediment yield of Mille river watershed at the lower Awash sub-basin using both climate and SWAT hydrological model. The climate model variables (precipitation and temperature) were obtained from Coordinated Regional Downscaling Experiment (CORDEX) of RACMO22 RCM climate model under HadGEM2-ES GCM and CCLM4 regional Climate model under ICHEC-ES global climate model with representative concentration pathway (RCP4.5) and (RCP8.5) scenarios. Bias correction was applied to climate variables and average value of the two RCM models arranged before future climate data’s transferred to hydrological model (SWAT) to simulate discharge and sediment for future time period. For model performance evaluation; Coefficient of determination (R2) and Nash Sutcliffe Efficiency (NSE) were used during calibration (1989-1997) and validated (1998-2002) period. The result of calibration and validation flow (R2 and NSE) are 0.68, 0.54 and 0.7, 0.6 respectively. Calibration and validation of sediment also provided a result of 0.81, 0.81 during calibration and 0.8, 0.79 during validation for R2, NSE respectively. Stream flow was simulated for two consecutive thirty years periods of (2031–2060) and (2061-2090) for both scenarios and compared with the base period (1986–2015) to investigate impact of climate change on hydrological process. The result obtained shows that overall mean annual precipitation projected to increase by 3.86% in 2050s and 7.82% during 2070s under RCP 4.5. For RCP 8.5 climate scenario precipitation increase by 4.61% during 2050s and 10.57% during 2070s. The hydrological response of a catchment also show an increment for the increasing precipitation amount such as sediment yield increase by 5.85% and 10.11% during 2050s and 2070s respectively under RCP 4.5 and 8.99% and 14.25% of increment occur in 2050s and 2070s respectively for RCP 8.5 climate scenario.
Temperature maximum also shows an increment with a magnitude of 0.11oc and 0.09oc under RCP 4.5 of the 2050s and 2070s on the other hand 0.2oc and 0.15oc increment was observed with in the same period of RCP 8.5. Temperature minimum will be increase for the future over the Mille watershed by 0.09oc and 0.15oc Under RCP 4.5 and by 0.13oc and 0.18oc under RCP 8.5 for the same time horizons of 2050s and 2070s.Overall there will be a variations of precipitation, temperature and sediment yield month to month and season to season. Therefore, it is important to consider this variation of sediment yield and climatic variable to draw appropriate guidelines for planning and management of different water resources project.
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Keywords
SWAT, GCM, RCM, Climate model, Bias correction, Climate Change