- Author: Michael D Cahn, Ph.D.
The California Irrigation and Management Information System (CIMIS) operates and maintains more than 145 weather stations throughout California. The CIMIS program is funded by the California Department of Water Resources. Most stations are located on or near agricultural land, and provide measurements of reference evapotranspiration (ETo), which can be used to estimate how much water to apply to crops. Hourly, daily, and monthly averages of data are available through the CIMIS web site (http://www.cimis.water.ca.gov). The website includes an option to automatically email data from selected stations on a daily or weekly schedule. In addition to ET data, CIMIS stations record precipitation, relative humidity, air and soil temperature, solar radiation, wind speed, and dew point. Besides irrigation management, weather data can be used for plant disease forecasts, for calculating insect and crop degree-days, and for determining wind speeds during spray operations. Water management agencies use historical reference ET data to determine pumping demands, and to estimate future ground water supplies using mathematical computer simulation models.
The Central Coast region currently has 16 active CIMIS stations (Table 1). Stations are located in Monterey, San Benito, Santa Cruz, Santa Clara counties. The newest station is #252 (Figure 1), located near Soledad CA on the east side of the Salinas Valley. CIMIS is a cooperative program, requiring collaboration between a local entity to provide land, maintain the site, and provide periodic servicing of the station. In some cases, stations are owned by the CIMIS program, but in many situations the weather stations are purchased through grant funding obtained by a local agency. Funding for station 252 was from a proposition 84 grant administered by the Coastal Conservation and Research Inc. The installation of the station was a partnership among Monterey County Resource Conservation District, UC Cooperative Extension (Monterey County), Dole Food Company Inc., CIMIS, Monterey Bay National Marine Sanctuary, and the Central Coast Wetlands Group (CCWG). Because CIMIS stations need to be sited on well-watered grass to provide accurate estimates of reference ET, funds from this grant were also used to establish 2-acres of grass surrounding the weather station and to install an underground sprinkler system.
Table 1. CIMIS stations located in the Central Coast region.
Figure 1. CIMIS station 252 located near Camphora-Gloria Rd, Soledad CA.
Even if a ranch has a private weather station, CIMIS data can still be useful. Many private weather stations are not instrumented to monitor ET or are not sited on a well-watered reference crop. Frequently private weather stations are located near a building, parking lot, or tree that can confound micro-climatic measurements. Over time instrumentation on weather stations can malfunction and record inaccurate data. The CIMIS system uses both an automated and manual quality assurance program to flag data that appear inaccurate or outside the normal range. CIMIS staff also service and check that the instruments are working properly. Additionally, CIMIS data are archived so that historical data can be accessed by users. CIMIS weather station data also contributes to Spatial CIMIS, a hybrid ET product that uses weather station and satellite data to provide reference ET estimates at approximately a 1-mile resolution. Spatial CIMIS reference ET data are also available through the CIMIS website.
During the past decade, significant progress has been made in adding new CIMIS weather stations or revitalizing old stations with improved site maintenance on the Central Coast. In addition to the Soledad station, Station 209 was established in West Watsonville, Station 211 was installed in Gilroy, and Station 210 was located in the Carmel Valley. Permanent grass was planted at station 129 in Pajaro and also at station 214 in South Salinas. Although progress has been made to increase the number and accuracy of CIMIS stations, weather stations are still lacking in some important Central Coast growing regions. Closer to the coast, the Castroville (#19) and North Salinas (#116) Stations are no longer reporting reference ET because the sites do not have sufficient grass cover to accurate measure ET. Also, the Green Valley road station (#111), which represents a warmer zone of the Pajaro valley no longer reports reference ET data due to insufficient grass cover at the site.
Having reliable long-term weather data from the main growing regions on the Central Coast is becoming more important for our region. As water demands continue to increase on the Central Coast, the agriculture community is under increased pressure to demonstrate efficient irrigation practices. Online irrigation scheduling tools such as CropManage and the Satellite Irrigation Management Support (SIMS), use CIMIS data to help growers quickly determine crop water needs. These tools can also help growers justify water needs of their crops. To comply with the Sustainable Groundwater Management Act (SGMA), water management agencies will need accurate reference ET data for developing ground water extraction plans. My hope is that through partnerships among local and state agencies, private land owners, and grower groups, we can add new or revitalize existing CIMIS stations so that all growing regions on the Central Coast have accurate weather data.
- Author: Michael D Cahn
- Contributor: Barry Farrara
Several strawberry growers have expressed interest in using evapotranspiration data for scheduling irrigations in strawberries, especially during the production season when crop water needs are greatest. Weather-based approaches to scheduling irrigations are used for many cultivated crops. Windspeed, air temperature, relative humidity, and solar radiation affect plant water-use, or more specifically the water lost by evaporation from the soil and by transpiration from the leaves of the crop. Using evapotranspiration (ET) data (evaporation + transpiration) from the California Irrigation Management Information System (CIMIS) the consumptive water use of a crop in units of inches or mm per day, can be estimated.
CIMIS ET data is available from the Department of Water Resources website (http://wwwcimis.water.ca.gov/cimis/welcome.jsp) for more than 120 locations in California, and is generated by weather stations located on irrigated grass, which serves as a reference crop. The MyCIMIS feature of the website allows the user to customize the reporting of CIMIS crop ET data, such as specifying type of weather data, stations, time period, and file format to display. MyCIMIS also allows the user to select for the data to be emailed to their account. Spatial CIMIS is another feature of the website that produces estimates of reference ET at a 2 km (1.2 mi) resolution using GOES satellite information and by triangulating humidity, temperature and wind speed data from the closest CIMIS stations to the point of interest. A Google map feature allows the user to locate a field of interest. Similar to MyCIMIS, a user can select to have updated Spatial CIMIS estimates of reference ET emailed.
ET can be estimated for a specific crop by multiplying reference ET data and the appropriate crop coefficient (Kc):
ETcrop = ETref × Kc
The value of Kc can range from almost 0 to greater than 1 and is closely related to the percentage of ground shaded by the canopy. Irrigation method and physiological stages, such as flowering and senescence are also factored into the crop coefficient. Crop ET values should be adjusted down by 20% to 30% for crops grown under macro tunnels or greenhouses because of shading.
Because accurate crop coefficients are not available for many crops, estimates of canopy cover serve as a close substitute for the Kc values. We have taken overhead photos of the UC strawberry variety Albion using an infra-red camera during the last 2 years. Photos were taken on a monthly schedule for fields with 48-, 52-, and 64- inch wide beds. After analyzing canopy images from 9 fields, we have estimated the Kc values on a weekly schedule during a 12 month period (Table 1). Because these data represent the average of several fields, values may need to be adjusted for site-specific conditions. Also, these Kc values for Albion represent Salinas and Pajaro Valley growing conditions and methods.
By irrigating enough to replace water lost by evapotranspiration it is possible to optimize irrigations for production and minimize percolation below the root zone. Also, it is possible to avoid under-irrigating during periods of high water consumption, which can result in stress and reduced growth. ETc estimates can be used to determine day by day soil water depletions from field capacity and thus can be used to also estimate when to irrigate. For detailed descriptions and examples of this technique, visit http://wwwcimis.water.ca.gov/cimis/infoIrrSchedule.jsp
Table 1. Estimated crop coefficient (Kc) for UC strawberry variety Albion.
48-inch bed width | 52-inch bed width | 64-inch bed width | |||||||
Plant Date | DAP | % canopy cover | Kc | % canopy cover | Kc | % canopy cover | Kc | ||
11/1/2011 | 0 | 1 | 0.02 | 1 | 0.01 | 1 | 0.02 | ||
11/8/2011 | 7 | 1 | 0.02 | 1 | 0.02 | 1 | 0.03 | ||
11/15/2011 | 14 | 1 | 0.02 | 1 | 0.02 | 2 | 0.03 | ||
11/22/2011 | 21 | 1 | 0.03 | 1 | 0.02 | 2 | 0.04 | ||
11/29/2011 | 28 | 2 | 0.03 | 1 | 0.02 | 3 | 0.04 | ||
12/6/2011 | 35 | 2 | 0.04 | 1 | 0.03 | 3 | 0.05 | ||
12/13/2011 | 42 | 2 | 0.04 | 2 | 0.03 | 4 | 0.06 | ||
12/20/2011 | 49 | 3 | 0.05 | 2 | 0.04 | 4 | 0.07 | ||
12/27/2011 | 56 | 3 | 0.06 | 2 | 0.04 | 5 | 0.08 | ||
1/3/2012 | 63 | 4 | 0.06 | 3 | 0.05 | 6 | 0.09 | ||
1/10/2012 | 70 | 5 | 0.08 | 4 | 0.06 | 7 | 0.11 | ||
1/17/2012 | 77 | 5 | 0.09 | 4 | 0.07 | 8 | 0.13 | ||
1/24/2012 | 84 | 6 | 0.10 | 5 | 0.08 | 10 | 0.15 | ||
1/31/2012 | 91 | 8 | 0.12 | 6 | 0.10 | 11 | 0.17 | ||
2/7/2012 | 98 | 9 | 0.14 | 7 | 0.11 | 13 | 0.20 | ||
2/14/2012 | 105 | 10 | 0.16 | 9 | 0.13 | 15 | 0.23 | ||
2/21/2012 | 112 | 12 | 0.18 | 10 | 0.15 | 18 | 0.26 | ||
2/28/2012 | 119 | 14 | 0.21 | 12 | 0.18 | 20 | 0.29 | ||
3/6/2012 | 126 | 16 | 0.23 | 14 | 0.21 | 23 | 0.33 | ||
3/13/2012 | 133 | 18 | 0.27 | 16 | 0.24 | 26 | 0.37 | ||
3/20/2012 | 140 | 21 | 0.30 | 19 | 0.28 | 29 | 0.41 | ||
3/27/2012 | 147 | 23 | 0.33 | 22 | 0.32 | 33 | 0.46 | ||
4/3/2012 | 154 | 26 | 0.37 | 25 | 0.36 | 36 | 0.50 | ||
4/10/2012 | 161 | 29 | 0.41 | 28 | 0.40 | 40 | 0.54 | ||
4/17/2012 | 168 | 32 | 0.44 | 32 | 0.44 | 43 | 0.58 | ||
4/24/2012 | 175 | 35 | 0.48 | 35 | 0.49 | 47 | 0.62 | ||
5/1/2012 | 182 | 38 | 0.52 | 39 | 0.53 | 50 | 0.66 | ||
5/8/2012 | 189 | 40 | 0.55 | 43 | 0.57 | 54 | 0.70 | ||
5/15/2012 | 196 | 43 | 0.58 | 46 | 0.61 | 57 | 0.73 | ||
5/22/2012 | 203 | 46 | 0.61 | 49 | 0.65 | 60 | 0.76 | ||
5/29/2012 | 210 | 48 | 0.64 | 53 | 0.69 | 62 | 0.79 | ||
6/5/2012 | 217 | 50 | 0.66 | 55 | 0.72 | 65 | 0.81 | ||
6/12/2012 | 224 | 52 | 0.69 | 58 | 0.75 | 67 | 0.83 | ||
6/19/2012 | 231 | 54 | 0.71 | 61 | 0.77 | 69 | 0.85 | ||
6/26/2012 | 238 | 56 | 0.72 | 63 | 0.79 | 70 | 0.87 | ||
7/3/2012 | 245 | 57 | 0.74 | 65 | 0.81 | 72 | 0.88 | ||
7/10/2012 | 252 | 59 | 0.75 | 66 | 0.83 | 73 | 0.89 | ||
7/17/2012 | 259 | 60 | 0.76 | 68 | 0.84 | 74 | 0.90 | ||
7/24/2012 | 266 | 61 | 0.77 | 69 | 0.85 | 75 | 0.91 | ||
7/31/2012 | 273 | 61 | 0.78 | 70 | 0.86 | 76 | 0.92 | ||
8/7/2012 | 280 | 62 | 0.79 | 71 | 0.87 | 76 | 0.92 | ||
8/14/2012 | 287 | 63 | 0.79 | 71 | 0.88 | 77 | 0.93 | ||
8/21/2012 | 294 | 63 | 0.80 | 72 | 0.88 | 77 | 0.93 | ||
8/28/2012 | 301 | 64 | 0.80 | 72 | 0.89 | 78 | 0.94 | ||
9/4/2012 | 308 | 64 | 0.81 | 73 | 0.89 | 78 | 0.94 | ||
9/11/2012 | 315 | 64 | 0.81 | 73 | 0.90 | 78 | 0.94 | ||
9/18/2012 | 322 | 65 | 0.81 | 74 | 0.90 | 79 | 0.95 | ||
9/25/2012 | 329 | 65 | 0.82 | 74 | 0.90 | 79 | 0.95 | ||
10/2/2012 | 336 | 65 | 0.82 | 74 | 0.90 | 79 | 0.95 | ||
10/9/2012 | 343 | 65 | 0.82 | 74 | 0.90 | 79 | 0.95 | ||
10/16/2012 | 350 | 65 | 0.82 | 74 | 0.91 | 79 | 0.95 | ||
10/23/2012 | 357 | 65 | 0.82 | 74 | 0.91 | 79 | 0.95 | ||
10/30/2012 | 364 | 66 | 0.82 | 75 | 0.91 | 80 | 0.95 |
- Author: Michael D Cahn
I have heard growers complain that the nearest CIMIS station is too far away from their ranch to provide accurate reference evapotranspiration (ETo) estimates. The CIMIS staff have recently improved the spatially accuracy of ETo estimates. CIMIS ETo estimates can now incorporate solar radiation data from the Geostationary Operational Environmental Satellite (GOES). GOES is the satellite that monitors ocean temperatures (think El Niño). The data (Figure 1) has a spatial resolution of 2 km (1.25 mi) so local effects of cloud cover and fog can be factored into ETo estimates. Relative humidity, air temperature, and wind speed data which are also required for the ET estimates are estimated by triangulating from stations closest to the location of interest. The more CIMIS stations operating in your region, the more accurately CIMIS can estimate ET for your field. Finally, like “MyCIMIS,” the spatial CIMIS reports can be emailed to you daily or weekly and in multiple file formats.
You can access spatial CIMIS ETo data from the CIMIS website (wwwcimis.water.ca.gov)
- Log on to MyCIMIS (you may need to set up a user account which is free).
- Go to the spatial CIMIS tab.
- Click on the link “Map Reports.”
- Choose the option “Map Coordinates” to bring up Google Mapping tool (Figure 2).
- Select the fields for which you would like to have spatial CIMIS ETo estimates (Figure 3).
- Select if you would want the spatial CIMIS report emailed daily or weekly or not emailed (Figure 4).
- Select the units for the data (english/metric), start and end dates, and file format. Note that csv format can be imported into spreadsheet programs like excel (Figure 5).
Figure 1. Map of solar radiation (right) and daily reference ET estimates from GOES data for California on May 10 , 2010. Solar radiation is expressed in units of MegaJoules/m2 . ET estimates are expressed in millimeters.
Figure 2. Selecting “map coordinate” option brings up the google map screen.
Figure 3. Fields of interest can be selected by zooming in on the Google Map screen. Longitudes and latitudes of locations are displayed below the map.
Figure 4. After selecting fields of interest, the user chooses email, unit, date, and format options, and submits the query.
Point | Lat | Long | Date | CIMIS ETo (in/day) | Sol Rad (Ly/day) |
1 |
36.82 |
-121.78 |
5/5/2010 |
0.16 |
640.93 |
1 |
36.82 |
-121.78 |
5/6/2010 |
0.18 |
637.74 |
1 |
36.82 |
-121.78 |
5/7/2010 |
0.17 |
654.02 |
1 |
36.82 |
-121.78 |
5/8/2010 |
0.016 |
650.08 |
1 |
36.82 |
-121.78 |
5/9/2010 |
0.13 |
514.43 |
1 |
36.82 |
-121.78 |
5/10/2010 |
0.1 |
353.03 |
1 |
36.82 |
-121.78 |
5/11/2010 |
0.15 |
655.33 |
|
|
||||
2 |
36.86 |
-121.7 |
5/5/2010 |
0.17 |
661.39 |
2 |
36.86 |
-121.7 |
5/6/2010 |
0.19 |
656.88 |
2 |
36.86 |
-121.7 |
5/7/2010 |
0.18 |
662.51 |
2 |
36.86 |
-121.7 |
5/8/2010 |
0.16 |
657.43 |
2 |
36.86 |
-121.7 |
5/9/2010 |
0.13 |
481.99 |
2 |
36.86 |
-121.7 |
5/10/2010 |
0.09 |
274.04 |
2 |
36.86 |
-121.7 |
5/11/2010 |
0.16 |
671.71 |
|
|||||
3 |
36.93 |
-121.7 |
5/5/2010 |
0.17 |
663.62 |
3 |
36.93 |
-121.7 |
5/6/2010 |
0.19 |
668.97 |
3 |
36.93 |
-121.7 |
5/7/2010 |
0.18 |
655.7 |
3 |
36.93 |
-121.7 |
5/8/2010 |
0.17 |
662.72 |
3 |
36.93 |
-121.7 |
5/9/2010 |
0.12 |
426.91 |
3 |
36.93 |
-121.7 |
5/10/2010 |
0.1 |
304.96 |
3 |
36.93 |
-121.7 |
5/11/2010 |
0.16 |
672.15 |
Figure 5. Example of Spatial ETo data imported into excel from an emailed CIMIS report. First column refers to field number.
- Author: Michael D Cahn
Access to weather data from the California Irrigation Management and Information System (CIMIS) has become easier than ever due to improvements in the website (www.cimis.water.ca.gov). CIMIS is managed by the CA Department of Water Resources.
CIMIS is a network of more than 120 weather stations that operate through out the agricultural regions of California. Currently, 13 stations are located on the central coast (Figure 1). All stations record relative humidity, air temperature, wind speed and direction, and solar radiation, and are located above a standard crop of grass or alfalfa, which are referred to as reference crops. Using these weather data and a mathematical model (Penman-Monteith) , potential crop water use, also called evapotranspiration (ETo), of the reference crop can be estimated. A crop coefficient is used to adjust the reference evapotranspiration data to evapotranspiration estimates for other crops, such lettuce, strawberry, or celery. CIMIS weather stations also monitor precipitation and soil temperature, and the stations calculate dew point, net radiation, and vapor pressure from the collected data.
The CIMIS staff has made many improvements in managing the weather data over the years. They use computer algorithms to check for outlying values which are flagged in reports. They have incorporated google maps to help you locate CIMIS stations near your fields (Figure 1), and they have incorporated Satellite weather data to help improve the spatial resolution of CIMIS evapotranspiration estimates.
Perhaps most importantly, the CIMIS staff has simplified getting access to the data. You can have the data emailed to you at a specified interval and also you can specify the format of the data (excel, web report, etc):
- Go to the CIMIS website and sign up for a user ID and password on the My CIMIS tab. (There is no cost for signing up and CIMIS does not send you annoying email solicitations).
- After logging on at the My CIMIS tab, select the station(s) from which you would like to receive weather data. Add the stations to a list.
- Under My Custom Report select “customize” to create a report. Choose the file format, station list, weather parameters, and time period (1 week, 2 week etc) that the report should cover (Figure 2). You can check the box to schedule the report to be automatically emailed to you (Figure 3). Note that the CSV format can be imported into Excel. The web report can be viewed directly from your web browser.
Figure 1. Location of currently operating CIMIS weather stations on the central coast as viewed from station location map under the Spatial CIMIS tab. Station numbers are displayed in the white rectangles.
Figure 2. User can select weather data and file format on the Custom report screen of My CIMIS tab.
Figure 3. User can select to have report emailed on the Custom report screen of My CIMIS tab.