Mekonnen H Daba
This paper estimates the runoff sensitivity to change in temperature and rainfall by using Soil and Water Assessment Tool (SWAT) hydrologic model. Rainfall and temperature were perturbed to study the runoff sensitivity to these climate variables. Rainfall and Temperature play main role in the accessibility of runoff by influencing the contribution and timing of water sources. The SWAT model was run with monthly station-based temperature and rainfall data for the whole upper awash sab-basin (1980-2010). The hydrological model was calibrated for eight years (1993-2000), and the simulation results were validated with the historical stream-flow for four years (2001-2005) at outlet of Hombole gauging station. The impact of temperature and rainfall changes on the runoff in the sub-basin was estimated by using a sensitivity analysis; through the calibrated and validated SWAT hydrological model. The SWAT model has been used to study the impact of possible hypothetical scenarios of rainfall and temperature on the annual runoff of the Awash sub-basin. This was achieved through both separated and combined use of changes in the amount of rainfall (+/-20% and increase temperature (warming of up to 5°C). The results shown that runoff was sensitive to rainfall and temperature changes in the study area. It has been revealed that 1, 2, 3, 4 and 5°C increases of the annual temperature lead to reduces annual runoff by -0.085, -0.88, -1.75, -2.55 and -3.30% respectively. The runoff has a positive correlation with rainfall change; but, a negative correlation with temperature change. The results reveal that runoff was more sensitive to rainfall than that of temperature rise. Increased/decreased rainfall by 10% will result in increased/reduced annual runoff by 22% and 21% respectively. Generally, the results showed that changes in the climate variables had a significant effect on water availability.
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