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.