NEWSLETTER ARTICLES

Strawberries, Soils and Water

CIMIS WEATHER STATIONS

CIMIS stands for the California Irrigation Management Information System. The CIMIS program was developed by the University of California during a four-year research proram.

The CIMIS weather station collects data on rainfall, solar radiation, air and soil temperature, relative humidity, and wind speed and direction. Each station automatically measures the weather data every minute and compiles the data for each hour. The central computer is located at the Department of Water Resources office in Sacramento and extracts the data every night from each weather station.

Northern Santa Barbara County has had 4 CIMIS weather stations to help with irrigation practices.

Santa Maria station No. 38 has been discontinued. The station was located on East Main Street at the De Bernardi Dairy since May 1983. My thanks to Ed and Norma De Bernardi for providing this location for us for the past 16 years. The station was discontinued because of a cropping change from pasture to corn.

Station No. 38 was one of the original 40 stations developed by the University. I participated with other University specialists in a 4-year research program to develop computerized weather information, evapotranspiration (ET_o) data and irrigation scheduling.

Today there are 104 operating weather stations.

Each CIMIS station is positioned on pasture grass to provide uniform environmental conditions between stations. The micrologger at each station automatically measures each weather sensor every minute and compiles the data hourly. The central computer at the DWR office in Sacramento phones each station every night and extracts the data from the micrologger. The CIMIS central computer summarizes the individual weather data and calculates evapotranspiration (ET_o) rates.

The calculated ET_o value is the estimated rate of water evaporated from the soil surface and transpired from grass pastures that are 6" tall. The ET_o data is reported as inches per day.

ET_o values vary according to geographic location, time of day, month of the year, and weather conditions. The main factors that influence ET_o values include solar radiation, relative humidity, air temperatures, and wind speed.

The ET_o at a specific location for an average year is referred to as normal year ET_o or historical ET_o. Normal year ET_o can be used as a reference to develop an average year irrigation schedule.

The ET_o values can be converted to other crop’s ET_o by using a crop coefficient (Kc).

Corp coefficients (Kc) are simply conversion factors that account for the difference in the evapotranspiration value (ET_o)) compared to other crops (strawberries, lettuce, celery, etc.). This calculation is very easy with the following formula:

The ET_o data is the daily evapotranspiration value for use in your irrigation scheduling for the various crops. The two publications listed below are helpful reference materials for you in using the CIMIS data. These publications can be obtained at our office, located at 624 West Foster Road, Suite A, Santa Maria. 805/934-6240.

#21426 Determining Daily Reference Evapotranspiration (ET_o). $1.50 #21427 Using Reference Evapotranspiration and Crop Coefficients to Estimate Crop Evapotranspiration: Agronomic Crops, Grasses, and Vegetable Crops. $1.75

CIMIS evapotranspiration data (ET_o) can be used as a guide for irrigation scheduling. Growers should verify each field condition by checking the soil moisture to accurately schedule irrigations. As growers prepare for higher water use, they need to manage the irrigations to increase water application efficiency and maximize crop production.

The location and starting date of the 3 other weather stations in northern Santa Barbara County are listed below:

The Guadalupe station (#120) is located on Hwy. 166 east of Guadalupe on the Guadalupe Ranch. It is approximately 6 miles from the ocean. Station #120 has been in operation since December 1993.

The Santa Ynez station (#64) is located east of Refugio Road on the Gainey Ranch. This station is approximately 21 miles from the ocean. Station #64 has been operating since November 1986.

The Cuyama station (#88) is located at the Cuyama Elementary School near Highway 166. Station #88 started operating in May 1989.

Station #38 was in a good location and, along with Guadalupe station #120, provided good weather data for the Santa Maria Valley. Again, my thanks to Ed and Norma De Bernardi for their cooperation for 16 years.