Figure 4 Regression of basin streamflow(m3/s) by its Rainfall(mm)
Conclusion
The upper Awash basin hydroclimate trend evaluation is carried for 25 years which is from 1991 to 2015 time series. This analysis is done with the basin’s hydroclimate elements precipitation, temperature, and streamflow. In the basin’s precipitation and climate trend analysis topographically, the basin is classified into highland, midland, and lowland. So, those three classes of the basin exhibited different precipitation and temperature trends.
The basin had 1019.41mm mean rainfall in the study time series. It got mean maximum rainfall 1339.78mm in 1993 and mean minimum rainfall 872.76mm during 1997. From the study station, maximum rainfall recorded is observed at Sebata station 3131.10mm by 1993. The Hombole station is the least rainfall recorded station 211.07mm by 1994.
The highland area meteorological evaluation resulted in an increasing and decreasing trend with both precipitation and temperature. Furthermore, during Gann a season with Addis Ababa, Addis Alem and Sendafa got increasing except Sendafa station; while decreasing trend observed during the Arfaasaa season and annually within all stations except Sendafa. Likewise, Addis Ababa station that considered as the temperature representative of the highland area got increased from both maximum and minimum temperatures. Midland stations revealed a decreasing trend in precipitation with seasonal change of temperature. The lowland area resulted in an increasing trend of precipitation with all stations except the Birraa season of Mojo station. Similarly, this part of the basin got an increasing trend of temperature.
The Mojo river sub-basin got a decreasing trend of streamflow except forGanna season. The Awash-Hombole sub-basin got decreasing annually except Berga and Melka kunture streamflow. During Ganna season, Awash Balo, Berga, and Melka Kunture exhibited an increasing trend while the rest got decreased.
Generally, the basin got maximum rainfall 1339.78mm in 1993 and minimum rainfall 872.76mm in 1997. Similarly, the basin maximum streamflow 39.4 by 1996 and minimum streamflow 9.92 m3/s in 2002. Precipitation of the basin increased annually and during theArfaasaa season with 30% of study stations (Mojo, Sendafa, and Asgori) only. The rest 70% of them exhibited a decreasing trend. But stations are insignificantly increasing while Ejere and Sebata decreasing insignificantly. Ganna seasons precipitation of study stations revealed 50% both increasing and decreasing trend. Similarly, basin streamflow exhibited change. Mojo’s main tributary is gauged at Mojo station and it resulted in a decreasing trend in wet seasons ad annually. During Arfaasaa, Ganna and Birraa seasons the tributary decreased. Annually and in the Birraa season, it decreased significantly at 90% and 95% significance level respectively.
Acknowledgment
The authors would like to appreciate National Meteorological Agency, Ministry of Water and Irrigation for the primary data provision and indebted to Jimma Institute of technology for funding the research.
Data sharing
The data that support the findings of this study are available from National Meteorology Agency. Restrictions apply to the availability of these data, which were used under license for this study. Data are available http://www.ethiomet.gov.et with the permission of National Meteorology Agency.
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