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INTRODUCTION
Agriculture is the mainstay of the Ethiopian economy in terms of income, employment and generation of export revenue. It directly supports 85% of the population of about 80 million and 80% of the export value in Ethiopia. Its contribution to gross domestic product (GDP), although showing a slight decline over the years, has remained very high, at approximately 43% by 2009 (Hagos et al., 2009; MoARD, 2010). Among the sub-sectors of agriculture, crop production is a major contributor to GDP accounting for approximately 28% in 2005/2006.
Agriculture in Ethiopia is mainly dependent on rainfed systems, and this dependency has put the majority of the Ethiopian population at the mercy of meteorological variability. With increasing meteorological variability due to changing climate, it is highly probable that the rainfed agriculture of Ethiopia will be vulnerable to its effects.
On the other hand, Ethiopia has 12 river basins with annual surface runoff volume of 124.5 km3 (Awulachew et al., 2007; MoWR, 2002) and estimated irrigation potential of 5.3 million hectares (Mha). The groundwater potential is estimated at 6.5 km3, which could realize about 1.1 Mha irrigation development (Awulachew, 2010). Moreover, ample rainfall is available to be tapped through rainwater management for household level small-scale irrigation. However, the developed irrigation from all these sources is so far, not more than 0.7 Mha (Awulachew, 2010).
Irrigation schemes in Ethiopia are classified on the basis of: the size of command area, technology used and management system. In the command area classification, they are classified as small (less than 200 ha), medium (200 to 3000 ha) and large scale (over 3000 ha) (Awulachew et al., 2005; Hagos et al., 2009; MoWR, 2002). The small-scale irrigation schemes are further classified into two major categories of modern and traditional schemes. Modern schemes usually have fixed or improved water control/diversion structures. Traditional schemes have no permanent diversion structures and are reconstructed every year from local materials by farmers themselves. The technological classification divides schemes according to the differences in the technology used to control and divert water. These influence water availability, efficiency of water use, and operation and maintenance costs. The third classification takes into account the management system, namely traditional,...