While the impact of climate change on rainfed crop yields has been extensively studied, the study of the effect on irrigated crop yields has been more challenging due to competing water uses. By combining a water model and a crop model within the MIT Integrated Global System Model (IGSM) framework (Sokolov et al., 2005), an integrated assessment of the effects of alternative climate policy scenarios on irrigated crop yields is applied to the United States (US). In this analysis, we consider the effect of water shortage for irrigation on the three most important crops for the U.S.: maize, soybean and spring wheat. We find that water shortage for irrigation is expected to reduce irrigated crop yields especially for maize.