Climate change is predicted to bring changes in weather and water availability. The effect on agriculture depends on the ability of producers to modify their practices in response to changing distributions. We develop a two-stage theoretical model of producer planting and irrigation decisions and use a unique dataset to empirically estimate how irrigated agricultural producers respond to changes in expected water availability and deviations from expectations. As water supplies decrease, producers respond by planting fewer acres and concentrating the application of water. Highlighting the importance of adaptation, failure to account for this behavioral response overstates climate change impacts by 29%.