Industry References that have been used by Gardenforms for many years for the understanding of Climate Zones to Water Regions for the State of California.  

Sunset Climate Zones
A great resource, garden literature reference in the green industry is that of Sunset Western Garden Book, where detail climate zones are presented when selecting plants for residential to that of commercial planting needs.
Water Use Classification of Landscape Species.  An industry irrigation guideline and specifications for over 3500 plants in six (6) water regions covering the entire State of Calfornia, which is referenced in the Landscape Architectural industry, as well and especially that of Irrigation Design and Consulting sector.

WUCOLS is an industry irrigation specification standards to determine water calculations (EAWU/MAWA) as well as city and county plan approvals throughout the state.  For additional information, please visit:
California Irrigation Management Information System (CIMIS).  An irrigation industry reference for State of California Evapotranspiration (ETo) to help in urban and agricultural planning in water management, scheduling and designing irrigation systems throughout California.
CIMIS ETo Map has been developed between the Department of Land, Air and Water Resources, University of California Davis and the Office of Water Use Efficiency, California Department of Water Resources.
USDA Hardiness Zones
In reference of the United States Department of Agriculture Zone Maps, based upon a plant hardiness.