Enviro-Geo, through a subcontract from Applied Geosolutions LLC, led the GIS component of this project that was funded by the California Energy Commission. DNDC was used to model irrigation water demand in California under historic (circa 1950) and contemporary (circa 2000) crop conditions. The study illustrates the large increases in crop irrigation and transpiration from historic to the contemporary state. County-level analysis demonstrates a strong seasonality in water use driven by climate and cropping practices, with the spring and summer months showing greatest irrigation water demand. Model results offer a baseline for contemporary and historic water demand that are suitable for both state and finer regional-scale applications.