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