Table 3 Trend analysis result of Precipitation
Hence highland stations are lacking temperature data, Addis Ababa
station is considered for the trend analysis. Thus, the station has
resulted in an increasing trend annually and during seasons.
Statistically annual trend of maximum temperature and duringGanna and Birraa seasons of minimum temperature
significantly increased. The detailed analysis is expressed in (table
3).
Seasonal and annual streamflow evaluation
Upper Awash river crosses the part
of the Ethiopian plateau via Bacho plain to the Koka dam that lays in
the main Ethiopian rift floor. Most of the main tributaries are heading
from a major urban area of the basin to the Awash River. Technically, it
is possible to classify these tributaries into Awash-Hombole and Mojo’s
main tributaries. Because the Koka dam inlet is mojo and awash-Hombole
river downstream.
Awash-Hombole is the main tributary from Awash-Melka kunture that comes
from Awash head flow with different tributaries and it joins with
Akaki’s main tributary at Geba Robi (472731.62m E, 953030.32m N) type
locality. This river crosses the three topographic classes (figure2)
used for the Metrologic trend. Dominantly it flows from highland and
midland topographic class.
Homogeneity test and autocorrelation detection are carried out before
the streamflow trend operation. Correlated annual data is detected at
Akaki and Mojo station. While Awash Bello, Berga, and Hombole stations
are correlated during the Bona season.
Berga and Akaki stations are significantly correlated during theArfaasaa season and Mojo station is correlated in Gannaseason. Significantly autocorrelated data trend analysis was operated
with modified Mann Kendall trend and uncorrelated data is operated with
original Mann Kendall trend test according to table 4.
Awash-Hombole upstream tributaries exhibit both a statistically
increasing and/or decreasing trend. Berga river significantly increasing
annually and during Arfaasaa and Bona seasons at 95%
significant level. During the Ganna season, it is significantly
increasing at a 90% significance level while during the Birraaseason it increases that doesn’t exhibit any statistical significance.
Contrarily, Akaki tributary heading from the Entoto scarp which
differentiates the Abay and Awash basin (Tenalem et al., 2008) resulted
in a statistically decreasing trend annually and during all seasons.
Awash Balo station resulted significantly decreasing trend during theArfaasaa season at a 5% critical value while Melka kunture,
Berga, Hombole and Holota stations resulted in a statistically
insignificantly increasing trend.