Effects of Rainfall Variability on Stream Flow and Its Impact on Small Scale Irrigation: The Case of Gedemso River, Central Rift Valley of Ethiopia

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Addis Ababa University


The availability and accessibility of water in space and time, both in quality and quantity, depends on the existing climate of an area and it could significantly vary with climate change. In developing countries, like Ethiopia where agriculture becomes the major source of the economy and dominantly rain:fed based. the farming system is vulnerable to climate change mainly rainfall variability. To reduce such impacts, introduction of irrigation system is taken as one major solution. In this regard. development of sustainable irrigation requires reliable agro-meteorological data and irrigation management system. Therefore, this is study aimed at analyzing rainfall variability, which is leading to stream flow fluctuation and its impact on Gedemso SSl scheme in central Rift Valley region of Ethiopia. Five stations rainfall data, stream flow gauged data, topographic map of the catchment, Digital Elevation Model and data collectedji-om irrigation beneficiary households were major data types used. Data analysis was undertaken using descriptive statistical tools and 1DW spatial interpolation using SPSS and ArcG1S software respectively. The analysis of rainfall variability over the catchment resulted in coefficient of variation of 55.25%, 27, 49%, and 14.7% during Bega (October-Januwy), Belg (February-May) and Kiremt (Jun-September) seasons respectively. Years of low rainfall with values less than one standard deviation below the mean. i.e., 1997 and 2002 were drought year. The variability of rainfall and stream flow has strong positive correlation with r value of a 719 and R2 of 63.5%. The study also investigated the existence of irrigation hazards associated with problems of stream fluctuation, canal structure and water use management, which was explained by 53% decline in tomato yield per hectare observed during low stream flow. Therefore, in order to have sustainable irrigation development; well designed canals, sound water use management plan and best irrigation system technology should be promoted and implemented. Key Words: Climate Change, Climate Variability, Rainfall variability, Stream flow, Small Scale irrigat ion



Climate Change, Climate Variability, Rainfall variability, Stream flow, Small Scale irrigat ion