This paper assesses the potential effects of climate change and adaptive management on irrigation water supply in the Cache Creek watershed in California. Our model, built using the Water Evaluation And Planning (WEAP) system, is calibrated using historical data (1971-2000) on streamflow, irrigation deliveries, and reservoir operations. We examine three adaptation scenarios to 2099: (1) changes in cropping patterns based on econometric forecasts, (2) a shift toward a more diversified and water-efficient cropping patterns, and (3) a combination of irrigation technology improvements and changes in cropping patterns. Maximum applied water savings occur by combining a diversified water-efficient cropping pattern with irrigation technology improvements, which decreases demand to levels 12% below the historical mean, thereby also reducing groundwater pumping.