100.6 ° F
Full Weather
Sponsored By:

CIMIS Can Help You Know When and How Much to Water

Sponsored by:

By Rebecca Miller-Cripps, the UCCE Master Gardener

With the advent of summer and warm weather, the time is right to talk about saving water (and money) while keeping lawns and gardens green and healthy. Between 40% and 50% of California´s water is used outdoors. Water in the outdoors disappears by three methods. It soaks into the ground (infiltration), it evaporates into warm air or wind (evaporation), or plants take the water up through their roots, use it in metabolic processes, and release it as water vapor through their leaves (transpiration).

For many of us, the water we use for irrigation comes directly from public water treatment systems, thus causing an increase in our water bills each summer. Given the sloping terrain in the foothills and the hot, dry climate, it´s difficult to know how often to water, for how long, and how much water to apply at one time. So it makes sense to manage our irrigation scheduling, for plant health, for budget health, and for resource conservation.

CIMIS may supply some of those answers. The acronym CIMIS stands for the California Irrigation Management Information System. Originally developed by the University of California at Davis as a management tool for agriculture, CIMIS is now managed by the California State Department of Water Resources (DWR). It is used to supply data to growers, ranchers, researchers, home owners, golf courses, and other water users. Schools use CIMIS data for educational purposes, municipalities use its calculations for urban landscape planning and management.

What is CIMIS and what does it do? CIMIS is a network of over 120 weather stations installed throughout the state of California. Each weather station is approximately six feet (two meters) tall and contains instrumentation to measure solar radiation, soil and air temperature, wind speed and direction, humidity, and rainfall. Once each minute a data logger collects all the weather information, then creates an hourly average. After 24 hours of hourly averages, it calculates a daily average and transmits the information to a central computer at DWR. This information is used to calculate the amount of water transpired and evaporated (evapotranspiration or ETo) in the area surrounding that particular weather station. Evapotranspiration calculations, in turn, help everyone in the local area know how much water to supply to their gardens, lawns, pasture, park or golf course.

Anyone can access CIMIS information by going to the website for a sample report. Farm bureau publications print the information for their local readership. Log on to the CIMIS website, and look around. You´ll find information about the system, information to help you schedule your own irrigation and explanations of a “water budget.”

Unfortunately, when you click on the “data” link, you´ll discover that there´s no data for Tuolumne County. The foothills are sadly underrepresented in the CIMIS weather station network.

A collaborative effort between DWR, the Tuolumne County Master Gardeners, Tuolumne Utilities District (TUD), and Mountain Springs Golf Course is working to change that situation. Potential sites were identified last year and CIMIS representatives from the Department of Water Resources in Sacramento spent a day touring the potential sites. DWR chose Mountain Springs as the best site to provide weather data needed to calculate ETo.

Weather station equipment has been purchased by Tuolumne Utilities District and is awaiting installation. Unfortunately, another obstacle has developed. CIMIS needs to rely on a 24-hour dedicated phone line for data transmission—the chosen site is not close to a phone line. Cellular phone service has proven unreliable and DWR is unwilling to allow the station to go “on-line” with cellular or telemetry data transmission. Further collaboration, trenching and phone line installation will be required.

If you´re interested in more information about CIMIS, the 120-plus weather stations already installed in California, and how that information can help you make decisions about watering your lawn, go to Or call Master Gardeners at 533-5696. We´re volunteers for the University of California and we´re willing to come to your home, free of charge, to help you test your sprinklers or figure out ways to save water and money as you irrigate. For additional information about how to test your sprinkler output and to determine effective watering schedules go to, click on “landscapes, gardens, and turf” and scroll to the bottom of the page to “UC Guide to Healthy Lawns.” Or go to and click on “Conservation.”

Smart watering just makes sense (dollars and cents). See you in the garden.

Rebecca Miller-Cripps is the UCCE Master Gardener Coordinator for Tuolumne County and wants to see a CIMIS station installed in Tuolumne County.