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.
