Impacts and uncertainties of climate change on stream flow of the Bilate River (Ethiopia), using a CMIP5 general circulation models ensemble

Abstract

The impact and uncertainty of climate change on stream flow of the Bilate River Watershed was assessed. Ensemble of 20 Coupled Model Intercomparison Project Phase 5 (CMIP5) general circulation models (GCMs) under two Representative Concentration Pathways and six GCM structures were selected to form 24 future climate scenarios for the watershed. Soil and Water Assessment Tool (SWAT) model was selected to simulate stream flow of the watershed. The respective statistical results of the coefficient of determination (R2), Nash-Sutcliffe coefficient (NSE) and percent bias (PB)  are 0.79, 0.78 and 0.56 for calibration period and 0.64, 0.60 and -21.7 for validation period which show that the model predicted the stream flow reasonably. The annual stream flow increased progressively throughout the century for all time periods. The increases under RCP 8.5 scenario are the larger compared to RCP 4.5 scenarios, approximately 42.42% during the 2080s period. The six GCMs selected to see the uncertainties related to GCMs suggest that the river flow will change by small amounts of -6.18 to 7.83% change compared with the baseline. The simulated runoff depended on the projected amount of rainfall embedded in the GCM structures selected to simulate the future climate and less dependent on the local temperature increment. Key words: Climate change, Bilate River watershed, stream flow, soil and water assessment tool (SWAT), uncertainty.