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Irrigated agriculture accounts for as much as 90% of the water consumed in arid parts of the world. In these areas the availability of water for competing agriculture, domestic, industrial, and environmental uses is quite low. Since agriculture is normally the largest consumer of water, and the historical owner of water rights, it is frequently proposed that water could be made available for the other uses by increasing irrigation efficiency through investment in new irrigation technology. Unfortunately, this position is often advocated without full knowledge of how increased irrigation efficiency is achieved and the broader implications of this process. This paper will explain the physical phenomena of irrigation management and plant growth involved in changing irrigation efficiency. The paper will then examine the conditions under which such changes might conserve water use in agriculture and make more available for other uses. The paper will also demonstrate conditions in which improvements in irrigation efficiency may actually reduce water availability for other uses, particularly in periods of drought or water shortage. Irrigation return flows from inefficient irrigation systems are normally an important part of the water supply to subsequent users in irrigated river basins. In such settings the process of increasing irrigation efficiency can actually decrease instream water supplies during periods of drought when compared to use of older, less efficient technologies.
agricultural production, growth, innovation adoption,irrigated farming, irrigation, irrigation systems, plant waterrelations, technology transfer, water allocation, water availability,water conservation, water management, water resources, water supply,water use, water use efficiency, adoption of innovations, water resourcemanagement, water supplies, watering, Plant Physiology and Biochemistry(FF060), Plant Water Relations (FF062), Plant Production (FF100), SoilWater Management (Irrigation and Drainage) (JJ800) (Revised June 2002)[formerly Soil Water Management], Water Resources (PP200), BiologicalResources (Plant) (PP720), Social Psychology and Social Anthropology(UU485) (New March 2000)