What is CIMIS?
The California Irrigation Management Information System (CIMIS) is a repository of climatological data collected at more than 125 automated active weather stations located throughout California. CIMIS was developed by the California Department of Water Resource and the University of California at Davis. Operational since 1982, it has recently been redesigned to use the latest database technology. Access is now possible with high-speed modems as well as through the Internet. Use of the CIMIS network is free and the system operates 24 hours a day, every day of the year except during maintenance hours. CIMIS helps agricultural growers and turf managers administering parks, golf courses and other landscapes to develop water budgets for determining when to irrigate and how much water to apply. Providing information for improving water and energy management through efficient irrigation practices is the primary use of the CIMIS system.

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How does CIMIS work?
Weather data is collected from each weather station site and automatically transmitted to a central computer located in Sacramento. The weather data is analyzed for accuracy, then stored to provide on-demand, localized information. Based on the weather data, the CIMIS computer estimates the amount of water evaporated from the soil and the amount used by irrigated grass (transpiration) at the weather station site. This combined value for pasture grass is called "reference evapotranspiration" or "ETo". Changes in ETo can be used as a guide to changes in crop or landscape water use. Using a conversion factor(s) and ETo, water use by a given crop or landscape can be estimated. These conversion factors are called crop coefficients (Kc). The values of these factors have been developed and continue to be developed for many trees, vines, agronomic crops, grasses, landscapes, and vegetable crops. These values and descriptions for how to use them are available from CIMIS.

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For more information, visit the State's CIMIS Web Page.