Table 4 Trend analysis result of Streamflow
Ganna season is known as the heavy season in the entire basin. But stations like Akaki, Hombole, and Holota have resulted in a decreasing trend while Berga, Melka kunture and Awash Balo are shown an increasing trend. During the Birraa season, Akaki station decreased significantly at 1% critical value while Holota station resulted in a statistically insignificant decreasing trend. But Awash Belo, Berga, Melka kunture and Hombole stations are increasing with statistically not significant. InBona which is the driest season of the sub-basin also exhibits both increasing and decreasing trend. Akaki, Awash Belo, Melka kunture and Berga resulted in a decreasing trend. But the first two stations significantly decreased at a 5% critical value. Contrarily, Holota and Hombole stations show insignificantly increasing trend. The basin resulted in an annually increasing trend within Melka Kunture, Berga and Awash Belo. The decreasing trend is observed with Akaki, Holota and Hombole stations. Though the basin decreased or increased with annal trend analysis, both are statistically not significant. Generally, from Awash-Hombole main tributaries, Awash-balo, Berga, and Melka-Kunture resulted in increasing trend annually and during Ganna season. Berga, Holota, Melka-Kunture and Hombole stations are increasing annually with statistically not significant.
Mojo station resulted in a significantly decreasing trend during theArfaasaa season at 1% critical value. During Ganna season Mojo station resulted in a decreasing trend. During the Birraaseason, Mojo stations decreased significantly at 1% critical value. During Bona which is the driest season of the sub-basin as expressed earlier Mojo stations show insignificantly increasing trend. But the station resulted in a decreasing trend annually.
Rainfall and Streamflow relationship
The rainfall influences streamflow of River basin. From the linear regression method, the upper Awash basin rainfall and streamflow are evaluation the relation is developed (fig 4).
The change in rainfall resulted in a change of streamflow (Figure 4). Basin streamflow change within the study time series is observed within the model’s observation confidence interval of 95% except for the 1996 steam flow. Generally, there is change observed within the basin both with rainfall and streamflow. Thus, the basin’s hydroclimate variated by 11.38% and 38.19% rainfall and streamflow respectively from the mean value within the study time series. The hydrologic variation could be from the existing climate change.