General circulation models predict significant and accelerating changes in local patterns of precipitation and temperature over the next century. The vulnerability of agriculture to climate change will depend on both the biophysical impacts of climate change on crop yields and on the agricultural system’s ability to adapt to changing production conditions. Shifts in the extent and distribution of irrigated and dryland production are a potentially important adaptation response. Farmer flexibility to adapt may be limited, however, by changing availability of irrigation water under future climate conditions. This study uses a suite of models to explore the biophysical and economic impacts of climate change on U.S. fieldcrop production under several potential future climate projections, and the potential limits and opportunities for adaptation arising from shifting regional water balances. Study findings suggest that the impacts of irrigation shortage on cropland use vary by region but that the net impacts on national production of surface-water irrigation shortages attributable to climate change are small relative to the direct biophysical impacts of climate change on yield.