Irrigation demand and supply, given projections of climate and land-use change, in Yolo County, California

We assess 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. Results show irrigation demand increasing by 26% and 32% under B1 and A2 baseline climate scenarios respectively in the latter part of the century under baseline climate scenarios. Irrigation water supply from upstream reservoir releases is less vulnerable, because of increased spring precipitation upstream. However, legal limits on reservoir releases mean that increased demand can only be met by increasing groundwater extraction. Increases in demand from climate change alone exceed applied water reductions from changing cropping patterns by an order of magnitude. 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.