The proliferation of the Internet and especially the World Wide Web has brought high technology information to the forefront of irrigation. As a result, there have been tremendous improvements in irrigation technology. For the California Irrigation Management Information System, better known by the acronym CIMIS, improving irrigation technology began long before the advent of the web.CIMIS is an integrated network of computerized automated weather stations located throughout California. The primary function of CIMIS is to provide reference evapotranspiration (ETo) data for irrigation scheduling and water management. ETo is an estimate of water use, in inches or millimeters, of a grass field that is an indication of water use by all kinds of vegetation. It is a combination of water removed by the plant and water loss by evaporation from the soil surface and plant leaves. Water agencies, farmers, farm advisors, irrigation specialists, golf course and park managers, and home owners use CIMIS ETo data to determine when and how much water to apply.
As of April 2000, there are 107 active stations, making CIMIS the largest standardized automated weather station network used for irrigation in the United States, and probably the world. Sixty-five stations are owned and maintained by cooperating private or public and agencies.
CIMIS weather stations are equipped with data loggers that collect hourly weather data throughout the day. At midnight, a microcomputer in Sacramento automatically begins the interrogation of stations by telephone. The microcomputer makes a connection with each weather station data logger, downloads data, and transfers the data to the main CIMIS computer. The CIMIS computer then performs three tasks:
(1) estimates ETo at each site,
(2) checks all weather data for accuracy, and
(3) stores weather and ETo data in a database to provide on-demand localized information.The modified version of the Penman equation is currently used to estimate ETo, and the Penmam-Montieth equation will be added to the system by the end of this year.
Using ETo data to schedule irrigation varies from simple back-of- the-envelope calculation to computer software. In fact, one can now schedule irrigation on the Web. CIMIS staff is aware of two sites that provide irrigation scheduling for free; they are the California Avocado Commission at www.avoinfo.com/growers and Wateright at www.wateright.org. Irrespective of the complexity of scheduling, however, the evapotranspiration rate for a particular crop or landscape (ETc) has to be determined. In its simplest form, ETc is calculated as ETc= ETo x Kc, where the crop coefficient, Kc, is a crop specific conversion factor.
CIMIS information and data are available at:
1. CIMIS -wwwdpla.water.ca.gov/cimis.html
2. Statewide IPM Project University of California-www.ipm.ucdavis.edu; and
3. Wateright -www.wateright.orgIndividuals and agencies that retrieve data the above sites further disseminate the data through telephone recordings, newspapers, industry publications, and radio. Also, several consultants use CIMIS data to provide services to growers, golf courses, and parks.
Simon Eching, Ph.D.
California Department of Water Resources