The Water Use Efficiency Branch of the California Department of Water Resources (DWR) manages, for the California Irrigation Management Information System (CIMIS) program, over 145 automated weather stations throughout the state of California. CIMIS was developed in 1982 to help agricultural producers and growers efficiently manage water resources, thereby saving water, energy, and money. Today, the CIMIS program has proved to be a valuable tool for all irrigators, including residential and commercial landscape professionals.
CIMIS weather stations continuously collect satellite data. A computer at the DWR headquarters in Sacramento retrieves this data and conducts quality control checks. Reference evapotranspiration (ETo) is then calculated and stored, along with climatic data, in the publically accessible CIMIS database. This data can help irrigators determine the appropriate amount of water, using real-time data, to apply to specific crops and landscape plants while avoiding overwatering and maximizing water resources and money saved.
The combined process of water loss to the atmosphere from soil and plant surfaces and transpiration from plants is defined as evapotranspiration (ET). ET is influenced by a myriad of factors, including relative humidity, hours of daylight, weather patterns, measurable precipitation amounts and ambient air temperatures. The ETo that CIMIS provides is a standardized ET based on the ET from the alfalfa or grass surfaces where each CIMIS station is located. This standardization is necessary because ET rates can vary greatly depending on soil factors and the type, density, and height of plants. Crop coefficients (Kc) can then be used to convert the CIMIS provided ETo into an actual evapotranspiration rate (ETc) for a specific crop in a local area.
Irrigators interested in utilizing CIMIS can access free limited data via the CIMIS website. For more detailed data, a free CIMIS account can be created and users can sign up to receive daily ETo data via email.
CIMIS spatial data for select San Diego County Regions for the past seven (7) days.
Data updated September 14, 2020