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Increased irrigation has been identified as an important potential adaptation to meet growing world food demand. Yet many of the world’s major irrigation regions are in arid and semi-arid regions that face climate change projections of hotter and drier weather. A growing body of analysis assesses irrigated agriculture impacts of climate change in such regions. Most published literature focuses on reductions in the mean-levels of freshwater supplies: less information is available on the potential impacts from changes in the reliability and quality of those diminishing water supplies. This article investigates the combined impacts on irrigated agricultural food supply from reduced, more variable and more saline water supply for a representative semi-arid irrigation region. Results indicate that understanding the potential impacts of climate change on agricultural production requires an understanding of not only how production may adapt to changes in mean water supplies, but also how it may respond to changes in water supply variability and salinity. We illustrate, using an Australian, Murray Darling Basin semi-arid region example, that ignoring these combined water-related climate effects lead to results that overlook thresholds where the structure of production and cost incurred fundamentally change above certain levels of variability and salinity. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.