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.