Impact Of Climate Change On Stream Flow (A Case Of Kulfo River)

Abstract

Nowadays the sign of climate change and its impact is revealing on different natural and manmade system. Accordingly, this impact is significant on the water resource system, especially on stream flow. Kulfo River is affected by climate change. As a result, the objective of this study is focused on investigate the impact of climate change on stream flow of Kulfo River which is found in Southern Ethiopia Rift valley Basin. Based on the objective of the study all the necessary data’s were collected from different sources, analysed an d finally prepared for model input .The Soil and Water Assessment Tool (SWAT) model was selected and applied to study the current (1987-2014) and two future scenarios 2050s and 2080s stream flow magnitude in the River. The flow parameters that significantly limit the stream flow in the River were assessed using SUFI2 in SWAT-CUP. Runoff curve number (CN2) was the most sensitive parameter that affects the hydrology of the watershed. After sensitive parameters were selected, the SWAT model was calibrated for the period of 1991 to 1999 and validated for the period of 2006-2011.In terms of hydrological model performance, Nash Sutcliffe Efficient (NSE) =0.68 and 0.78 for calibration and validation and coefficient of determination (R2 ) =0.81 and 0.92 for calibration and validation respectively, which resulted in good model performance while simulating flow parameters in the catchments. The future climate change impact studies on stream flow of the Kulfo River were done based on the synthetic scenario approach. The future projection range of temperature and precipitation was adopted based on the IPCC fifth assessment report as 2.50C to30C for 2050s and 40C to 50C for 2080s and precipitation -20% to +20%, were applied to the calibrated and validated model in order to investigate the sensitivity of Kulfo Rive stream flow. Compared to the climate normal (baseline climate), the average annual stream flow of the Kulfo River is projected to increase by 5.2% and 5.42% in the year 2050s and 2080s respectively. In contrast it was found to give the maximum projected decrease (reduction) in discharge by -6.6% and -8.2% in 2050s and 2080s respectively. Increasing temperature by 0.5°C decreased stream flow rates by 2.86 % and 2.99%, in 2050s and 2080s respectively, while 10% drops in rainfall resulted in a stream flow reduction by 4.92% and 5.28% in 2050s and 2080s respectively. These results suggest that stream flow in the Kulfo River will be more sensitive to change in precipitation than to change in temperature.