Helpful Links

ET Overview

The following sections give a brief overview of evapotranspiration, otherwise known as ET on this website. Sections include an Introduction, Estimating ET, and the ETo Equations. Click on the “V” to the right of the section header to access the section.
  • Introduction
    Picture of a crop being watered Water is essential for all living things including plants. Precipitation and irrigation are the two primary sources of water for agricultural crops and landscape vegetation. Plant leaves and soil surfaces temporarily retain parts of water directly applied to them. As solar radiation hits such surface, it breaks the retained water molecules apart and changes liquid water into water vapor. The water vapor is transported away from the surface by winds. The process by which the water molecule is converted from liquid phase into the gaseous phase (and removed from the surface) is called evaporation.

    The water that is not retained by the plant and soil surfaces infiltrates into the soil. Plants extract the infiltrated water through their roots and transport it to their leaves for photosynthesis, a process by which plants produce glucose (sugar). In addition to water, plants need carbon dioxide (CO2) and light for photosynthesis. The light comes from the sun and CO2 comes from the atmosphere. In order to take atmospheric CO2 in, plants open their stomata, the microscopic pores on plant leaf surfaces, thereby exposing the water in the leaf to solar energy and wind. This results in a loss of water from within plant leaves to the atmosphere through the process known as transpiration.

    Evapotranspiration (ET) is the term used to describe the loss of water to the atmosphere by the combined processes of evaporation (from soil and plant surfaces) and transpiration (from plant tissues). Accurate estimates of ET are needed in many applications. In agricultural and landscape irrigation, for example, estimates of ET are necessary for system design, irrigation scheduling, water rights, water transfers, water resources planning, and other water related issues.

    As described above, three conditions must be met for ET to take place. First, water has to be present at the surface-atmosphere interface. Second, there must be some form of energy to convert the liquid water into a water vapor. This conversion requires large amounts of energy (about 540 Calories per gram of water at a temperature of 100 °C), which is usually provided by the sun. Third, there must be a mechanism to transport the water vapor away from the evaporating surface.

  • Estimating ET
    Many factors affect ET including: weather parameters such as solar radiation, air temperature, relative humidity, and wind speed; soil factors such as soil texture, structure, density, and chemistry; and plant factors such as plant type, root depth and foliar density, height, and stage of growth. Although ET can be measured using such devices as lysimeters, estimating ET using analytical and empirical equations is a common practice because measurement methods are expensive and time consuming. Most ET equations were developed by correlating measured ET to weather parameters that directly or indirectly affect ET. Since there are so many factors affecting ET, it is extremely difficult to formulate an equation that can produce estimates of ET under different sets of conditions. Therefore, the idea of reference crop evapotranspiration was developed by researchers. Reference ET is the ET rate of a reference crop expressed in inches or millimeters.

    Reference crops are either grass or alfalfa surfaces whose biophysical characteristics have been studied extensively. ET from a standardized grass surface is commonly denoted as ETo whereas ET from a standardized alfalfa surface is denoted as ETr. The American Society of Civil Engineers (ASCE) recommends the use of ETos and ETrs for grass and alfalfa surfaces, respectively, where "s" stands for standardized surface conditions. The weather stations are set up on standardized reference surfaces for which most of the biophysical properties used in ET equations are known. Using these known parameters and measured weather parameters, ET from such surfaces is estimated. Then, a crop factor, commonly known as crop coefficient (Kc), is used to calculate the actual evapotranspiration (ETc) for a specific crop in the same microclimate as the weather station.

    CIMIS is using a well-watered actively growing closely clipped grass that is completely shading the soil as a reference crop at most of its weather stations. Therefore, reference evapotranspiration is mostly referred to as ETo on the CIMIS web site. There are, however, a few CIMIS stations that are sited on alfalfa reference crop surfaces and therefore reporting ETr instead of ETo.

  • ETo Equations
    There are many theoretical and empirical equations to estimate ETo. The choice of any one method depends on the accuracy of the equation under a given set of conditions and the availability of the required input data. Climatic factors such as solar radiation, air temperature, wind speed, and relative humidity are measured at CIMIS weather stations. The equations below use calculations of intermediate values from these measured parameters along with analytical and empirical relationships. Measured and estimated values are used to calculate ETo.

    CIMIS uses the Penman-Monteith equation and a version of Penman's equation modified by Pruitt/Doorenbos (Proceedings of the International Round Table Conference on "Evapotranspiration", Budapest, Hungary. 1977). The Modified Penman employs a wind function developed at UC Davis and is therefore referred to as the CIMIS Penman equation in different literatures. CIMIS uses hourly weather data to calculate hourly ETo and adds them up over 24 hours (midnight to midnight) to estimate daily ETo.

    The Penman-Monteith (PM) equation used to estimate hourly ETo is the United Nations Food and Agricultural Organization's version that is described in Irrigation and Drainage Paper No. 56. However, the bulk surface resistance is adopted from the ASCE Task Committee on Standardization of Reference Evapotranspiration. PM equation derived ETo is a selectable value in the "Select Sensors" Sensor list and named Penman-Monteith ETo or "PM ETo" in data reports.

    CIMIS Penman
    The CIMIS version of the Pruitt/Doorenbos modified Penman equation uses a wind function developed at the University of California, Davis and unique cloud factor values for each station location to calculate "CIMIS ETo." Because of those modifications, the equation is referred to as the "CIMIS Penman" equation in various literature.
    Throughout this web site, reference evapotranspiration values calculated using the CIMIS Penman equation are referred to as ETo whereas those calculated using the Penman-Monteith equation are referred to as PM ETo.

    Current upgrade
    Both equations discussed above use hourly average weather data as an input to calculate hourly ETo. The 24 hourly ETo values for the day (midnight-to-midnight) are then summed to produce estimates of daily ETo.

    Although there is a version of the Penman-Monteith equation that directly calculates daily ETo from daily average weather parameters, CIMIS chose to sum hourly values for consistency with the daily CIMIS Penman method. Studies have shown that there are no statistically significant differences between PM derived ETo and CIMIS ETo.

Irrigation Overview

The following sections give a brief overview of irrigation. Sections include the following: Introduction, Water Budget, Crop Coefficients, Irrigation Scheduling, Irrigation System Efficiency, and Normal Year Irrigation Schedules. Click on the “V” to the right of the section header to access the section.

  • Introduction
    Picture of a crop being watered Plants need water to survive and grow. In humid areas, the water demands of most plants are met by rainfall. In arid and/or semi-arid regions however, plant water requirements are usually much more than what rainfall can provide. Therefore, additional water needs to be provided in the form of irrigation. The practice of irrigation has been around for thousands of years and has evolved into a science that deals with the study of soil-water-plant relationships.

    CIMIS is here to help California's irrigators manage their water resources efficiently. Over irrigating not only wastes water and resources, but also leaches nutrients away from plant roots. Conversely, if not enough water is applied, productivity of the soil is impaired – affecting plant development or possibly leading to the plant dying. Therefore, a major part of irrigation management is deciding when to irrigate and how much water to apply.

    Determining the inputs and outputs of water to and from the plant root zone is a very complex process. Using the water budget method and an irrigation schedule (see below) can assist users in their decisions about when to irrigate and how much water to apply.

    See below for more information on water budgets, crop coefficients, irrigation scheduling, and other resources. CIMIS Staff can also help point you in the right direction.

  • Water Budget
    Picture illustrating how water evaporates from soil Water budgeting monitors the balance between the inputs and outputs of water to and from the plant root zone. The method is similar to balancing a checkbook. Water budgeting inputs include rainfall, irrigation, dew, and capillary rise from ground water. The outputs include evapotranspiration, runoff, and deep percolation.

    Since 1982, CIMIS has provided reference evapotranspiration estimates and precipitation measurements.

    • Evapotranspiration is the loss of water to the atmosphere by the combined processes of evaporation from soil and plant surfaces and transpiration.
    • Transpiration is water transfer to the air up through the plant tissues from the roots.
    • Reference Evapotranspiration (ETo/ETr) is a term used to describe the evapotranspiration rate of a reference plant such as grass (ETo) or alfalfa (ETr). ET is expressed in either inches or millimeters.
    • CIMIS provides ETo estimates by measuring weather parameters such as wind speed, air temperature, and solar radiation at its weather station sites, and then calculates ETo values using the CIMIS Penman and Penman-Monteith equations.
    • Crop Coefficients (see below) are used with ETo to estimate the actual evapotranspiration (ETc) of a specific crop.

    The user must determine the remaining water budget components needed to use this method. Runoff and deep percolation can be estimated based on local factors such as soil properties and slope. Dew formation and capillary rise of ground water can also be estimated. However, estimation of the latter two parameters is a bit involved. Fortunately, these values are relatively small (depending on the specific situation) and can be ignored for most irrigated crops. Users need to estimate other local factors such as soil type, plant type, slope, rooting depth, and plant density.

    Please see the Irrigation Scheduling section below for more information.

  • Crop Coefficients
    Picture of a crop Coefficient The crop coefficient (Kc) is a dimensionless number (usually between .1 and 1.2) that is multiplied by the ETo value to create a crop evapotranspiration (ETc) estimate. The resulting ETc can be used to help an irrigation manager schedule when irrigation should occur and how much water should be put back into the soil. An example calculation follows:

    If ETo = 0.25 inches/day (for July 15, 1985) and Kc = 0.55 (for an orange tree in July) then, ETc = ETo x Kc = 0.25 inches/day x 0.55 = 0.1375 or 0.14 inches/day

    Crop coefficients vary by crop, stage of growth of the crop, and by some cultural practices. Citrus trees have smaller coefficients than peach trees (when the peach tree is at full cover). Crop coefficients for annual crops (row crops) will vary widely through the season, with a small coefficient in the early stages of the crop (when the crop is just a seedling) to a large coefficient when the crop is at full cover (the soil completely shaded). Almond orchards with cover crops between tree rows will have larger coefficients than almond orchards without cover crops.

    It is very important to understand that crop coefficients that should be used with CIMIS ETo (with grass as the reference crop) are those that were developed specifically for use with grass-referenced ETo.

    The University of California Cooperative Extension has prepared two leaflets on crop coefficients: Leaflet #21427, "Using Reference Evapotranspiration (ETo) and Crop Coefficients to Estimate Crop Evapotranspiration (ETc) for Agronomic Crops, Grasses, and Vegetable Crops" and Leaflet #21428, "Using Reference Evapotranspiration (ETo) and Crop Coefficients to Estimate Crop Evapotranspiration (ETc) for Trees and Vines." These crop coefficients are designed for use with CIMIS ETo data.

    Crop Coefficients for some agricultural crops and landscape plants can also be obtained from the following links:

    For additional information, please contact CIMIS.

  • Irrigation Scheduling
    Picture of a crop being watered A major part of any irrigation management program is the determining how often and- how much water to apply to the field. This decision-making process is referred to as irrigation scheduling

    The following is a short description of a simplified water budget method of irrigation scheduling, and how to use CIMIS ETo to help determine irrigation schedules:

    • The initial balance of water can be determined by direct observation or a thorough wetting of the root zone soil by irrigation or winter rains.
    • Daily quantities of ET are then subtracted until the soil water has been reduced to a desired level.
    • At that point an irrigation amount is applied equal to the accumulated ET used since the last irrigation, the soil profile is recharged to full capacity, and the cycle begins again.

    If full recharge is not desired or not possible, the new balance can be determined from the irrigation amount applied or by field observations. This method, however, may not work well at locations where contributions to crop water use from a water table or other source cannot be measured.

    Defined technical irrigation terms and a more in depth example follows:

    • Field capacity is the quantity of water stored in a soil volume after excess water drains down and out of the plant root zone.
    • Only a portion of the water content can be potentially taken up by the crop and this quantity is called "available water" (AW).
    • The amount of available water within the crop root zone at any given time is often called "soil moisture reservoir.”
    • Only a fraction of the reservoir is readily available to the crop without causing water stress.

    A major goal in good irrigation management is to prevent yield reducing crop water stress by maintaining the soil water content above a certain level. This is done by keeping track of soil water content and knowing how dry the soil can get before yield reducing crop stress will occur (referred to as the yield threshold depletion or YTD). The value of the YTD is mainly dependent upon the crop sensitivity to stress and root density. The ultimate choice of how much water to deplete before irrigating is made by the irrigation manager and depends upon cultural practices, labor, water deliveries, or other considerations. Irrigation is timed depending on a management allowable depletion (MAD), which is the percent of available water which the irrigator will allow plants to deplete before irrigating or the depth of water that the irrigator will allow plants to extract from the root zone between irrigations. Generally, the MAD is selected to be less than or equal to the YTD.

    ETc can be calculated with ETo from CIMIS and a crop coefficient (Kc) as ETc = ETo x Kc. These ETc estimates can be used to determine day by day soil water depletions by crop water use from field capacity and thus can be used to schedule irrigations.

    Table 1 is a sample of how a water budget would be calculated for a seed alfalfa field with the following properties:

    • Available water (AW) in root zone = 5.0 inches
    • Management allowable depletion (MAD)= 50% AW = 2.5 inches
    • Yield threshold depletion (YTD) = 2.6 inches.

    Date Effective Rainfall (in) Irrigation (in) Crop ET (in) Crop ET (in) Depletion (in)
    July 2 0.00 0.00 0.30 0.30 2.20
    July 3 0.00 0.00 0.19 0.49 2.01
    July 4 0.00 0.00 0.22 0.71 1.79
    July 5 0.00 0.00 0.28 0.99 1.51
    July 6 0.00 0.00 0.25 1.24 1.26
    July 7 0.00 0.00 0.26 1.50 1.00
    July 8 0.00 0.00 0.28 1.78 0.72
    July 9 0.00 0.00 0.32 2.10 0.40
    July 10 0.00 0.00 0.36 2.46 0.04
    July 11 0.00 2.50 0.40 0.36 2.14
    July 12 0.00 0.00 0.22 0.58 1.92
    July 13 0.42 0.00 0.11 0.27 2.23
    July 14 0.25 0.00 0.15 0.17 2.33
    July 15 0.00 0.00 0.25 0.42 2.08

           The budget record begins on July 1 with the total water content at field capacity or 2.5 inches MAD. On each day, ETc is added to the depletion on the previous day to obtain a new depletion value. A net of 2.50 inches was applied on July 11 because the depletion from field capacity was going to exceed both MAD and YTD. Effective rainfall, or amount of rainfall that contributes to the soil reservoir on July 13 and 14 was recorded and the depletion was adjust accordingly.

  • Irrigation System Efficiency
    The water budget method of irrigation scheduling can be used to determine when an irrigation should occur and how much water to replenish. It does not by itself determine how much water should be applied through the irrigation system or how long the irrigation system should be operated to apply the water. Determining the amount of water to actually apply through the irrigation system is done by dividing the amount of water required to replenish the soil reservoir by the efficiency of the irrigation system. Water that runs off the field or percolates below the root zone due to nonuniformity of the irrigation system does not contribute to the soil reservoir. For example, if 30 percent of the water applied runs off the field or percolate below the root zone, the irrigation efficiency is 70 percent and the required applied water for the July 11 irrigation would be:

    2.50 inches / 0.70 = 3.57 inches

    Therefore, the grower should apply a depth of approximately 3.6 inches to replenish the soil reservoir over the entire field. Any application of water over 3.6 inches would result in either excess runoff or percolation below the root zone.

    Determining the efficiency of an irrigation can only be done accurately by a system evaluation during an irrigation. Depending on the design, maintenance and management of an irrigation system, the efficiency can vary substantially. There are several government agencies and private consultants who can perform these evaluations.

  • Normal Year Irrigation Schedules
    A good planning tool for an irrigation manager is a normal year irrigation schedule. This is an irrigation schedule for a specific field and crop that is based on historical weather data. This schedule can be developed before the irrigation season and can be used to estimate when irrigations will most likely be needed during the season.

    A normal year schedule can be updated during the irrigation season using current ETo information. This will result in changes in irrigation dates or amounts that reflect current conditions. For example, lower than normal ETo values would result in either more time before the next irrigation or a smaller amount of required water for the same irrigation date. This updating can be done on paper or by using a computer system.

    Many resources are available to help you create an irrigation schedule that meets your specific needs. For further help, refer to our listings of publications, consultants, and software vendors in the tabs above.

Data Overview

The following sections give a brief overview of CIMIS Data. Sections include the following: Data Formats, Data Size, Quality Control, and Data Types. Click on the “V” to the right of the section header to access the section.

Picture of a crop being watered

This tab provides a brief overview, but no data. Please refer to the DATA tab to view limited hourly, daily, and monthly reports; access FTP reports; or log in to access unlimited reports; schedule emailed reports, and set default preferences.

  • Data Formats
    Hourly, daily, and monthly data can be retrieved from the CIMIS web site in the following data formats:

    Web Report:   Web Reports display in the browser. This format provides for ease of viewing and moving through the data.
    XML Report:   Extensible Markup Language (XML) provides a flexible and easy way to integrate CIMIS data into your information system.
    CSV Report:   Data in the Comma separated values (CSV) format can be opened in a spreadsheet application such as Excel, or in Notepad or Wordpad.
    PDF:   Portable Document Format (PDF) is a file format that captures all the elements of a printed document as an electronic image that can be viewed or printed. It can provide very good printing quality. You need to have Adobe Acrobat to get the PDF format from the CIMIS web site.
  • Data Size
    The following is a list of allowable data sizes for the different data formats while retrieving hourly, daily, and monthly data reports. Due to resource limitations, CIMIS has restrictions on the data file size a user can download. One can retrieve, however, as much data as there exists for a particular station, by adjusting the date range and number of sensors chosen.

    The data file size is expressed as records with the following typical formula:
    Records = (station count) * (days) * (hours)

    Hourly Report
    Report Format/ Max Records   Example

    Web Report / 30,000   1 station, 1 year = 8,760 records
    XML Report/ 50,000   2 stations, 1 month = 1,440 points
    CSV Report/ 50,000   1 station, 5 years = 43,800 records
    PDF Report / 2,000   1 station, 1 month = 7,200 points
    Daily Report
    Report Format/ Max Records   Example

    Web Report / 16,000   5 station, 3 years = 5475 records
    XML Report / 16,000   8 stations, 1 year = 2920 records
    CSV Report / 16,000   5 stations, 5 years = 9125 records
    PDF Report / 1,000   8 stations, 3 months = 720 records
    Daily ETo Variance
    Report Format/ Max Records   Example

    Web, XML, & CSV Reports / 16,000   1 station, 5 years = 1,825 records
    PDF Report / 1,000   2 stations, 1 year = 730 records
    Monthly Report
    Report Format/ Max Records   Example

    Web, XML, & CSV Reports / 40,000   10 station, 5 years = 600 records
    PDF Report / 9,000   10 station, 2 years = 240 records
    Monthly Average ETo Report (No Limit)

  • Quality Control
    Picture of a QC Overview Data received by CIMIS servers are quality tested and flagged if they fall outside a set standard. Missing data are also flagged. Quality control (QC) of the CIMIS data is required to ensure that the measured weather data and calculated reference evapotranspiration (ETo) values are of high quality.

    Quality tested data are stored in a relational database for on-demand access by CIMIS users. The quality control flags identify specific data problems. While their immediate use is to inform users of data credibility as related to the set of standards, the flags are also used to monitor sensor performance on a daily basis. Quality Control flags also assist in observing long-term trends in data quality and test the performance of specific stations. Local personnel examine flags daily to detect potential malfunction of station sensors and schedule repair trips.

    Prior to 1995, the quality control program data standards used were based on theoretical and historical data limits for the period 1982 through 1985. Flags created using this standard are referred to as former flags. On January 1, 2001, a new QC program based on CIMIS historical data took effect. Data averages (means) and standard deviations for each station, theoretical limits, and some of the procedures described by Meek and Hatfield (1994) were used to test data quality. Flags created using this new standard are referred to as current flags. For stations that have less than five years of historical data, regional statistics are used. We also quality tested and flagged historic data for the period 1995 through 2000 using the new criteria.

    Further information on current and former QC flag summaries and hourly and daily flags can be obtained from the following sources:

    Former Flags
    Current Flags
    Current QC Procedures

    If you have questions, you may write or email Simon Eching or Bekele Temesgen:

    Department of Water Resources
    Office of Water Use Efficiency
    P.O. Box 942836
    Sacramento, CA 94236-0001


    • Meek, D.W. and Hatfield, J.L.1994. Data quality checking for single station meteorological databases. Agricultural and forest meteorology 69:85 -109.
  • Data Types
    The following weather data are either measured at the CIMIS weather stations or calculated from measured values:

    Measured Values
    Solar Radiation:   The total incoming solar radiation is measured using pyranometers at a height of 2.0 meters above the ground. Solar radiation data is used in the calculation of net radiation. Hourly, daily, and monthly average solar radiation data are available.
    Air Temperature:   Air temperature is measured at a height of 1.5 meters above the ground using a thermistor. Air temperature is used in the calculation of other parameters such as dew point temperature, vapor pressure, net radiation, and reference evapotranspiration. Hourly, daily, and monthly data are available. Maximum, minimum, and average air temperatures are reported for the daily and monthly data.
    Soil Temperature:   Soil temperature is measured at 15 centimeters (6 inches) below the soil surface. It is measured using a thermistor with resistance that varies with temperature. Soil temperature is commonly flagged because soils, especially those with high clay content, may crack and let warmer air reach the sensor, resulting in high soil temperature values. Wildlife holes near the thermistor may also cause an error. Hourly, daily, and monthly soil temperature data are available. Maximum, minimum, and average values are reported for the daily time steps.
    Relative Humidity:   Relative humidity is the ratio of the actual amount of water vapor in the atmosphere to the amount the atmosphere can potentially hold at a given air temperature. It is expressed as a percentage. The relative humidity sensor is sheltered in the same enclosure with the air temperature sensor at 1.5 meters above the ground. Relative humidity values are used in the calculation of dew point temperature, vapor pressure, and reference evapotranspiration. Hourly, daily, and monthly data are available. Maximum, minimum, and average relative humidity data are reported for the daily and monthly reports.
    Wind Speed:   Wind speed is measured using three-cup anemometers at 2.0 meters above the ground. The threshold wind speed is 1.0 mph. The sensor can withstand wind speeds of up to 120 mph. Wind speed values are used in the calculation of total wind run, resultant wind, wind roses, and reference evapotranspiration. Hourly, daily, and monthly values of average wind speed are available.
    Wind Direction:   Wind direction is the direction the wind is blowing from. It is measured using a wind vane at 2.0 meters above the ground. Wind direction values range – in the clockwise direction – from zero to 360 degrees (both being true north) and are adjusted for declination of the Earth's axis. Wind direction is only available in the hourly reports. On daily time steps, wind direction is used in the development of wind roses. Standard Deviation of Wind Direction is reported in the hourly data.
    Precipitation:   Rainfall is measured using tipping bucket rain gauges. While maintaining a standardized grass or alfalfa surface at the CIMIS weather stations, sprinkler irrigation water may sometimes drop into the rain gauges. CIMIS staff adjust the corrupt rainfall data most of the time but some may slip their scrutiny. Therefore, users are advised to pay attention to the precipitation data and notify us of any suspicious data.
    Calculated Values
    Net Radiation:   Net radiation is the net radiant energy available at the surface of the earth for evaporating water, heating the surface, and heating the air. It is calculated as a balance between the incoming and outgoing radiant energies. Hourly and daily net radiation data are available.
    Reference Evapotranspiration:   Reference evapotranspiration is evapotranspiration from standardized grass (ETo) or alfalfa (ETr) surfaces. The CIMIS ETo and ETr values are calculated using the modified Penman (also known as the CIMIS Penman) and the Penman-Monteith equations. Reference evapotranspiration is often referred to as ETo on the CIMIS web site because most CIMIS weather stations are located on actively growing grass. Hourly, daily and monthly data are available.
    Resultant Wind Speed:   Resultant Wind Speed is the magnitude of a vector that results from averaging individual wind vector measurements over a given period of time. A vector is a quantity that has a magnitude and direction. CIMIS reports resultant wind speed for hourly data.
    Wind Rose:   Wind Rose shows the distribution of wind speeds and the frequency of the varying wind directions. Wind directions are grouped into different sectors known as bins. Wind Roses reported in CIMIS have eight bins. Wind Rose data is currently available for the daily time step only.
    Wind Run:   Wind Run is the total distance the wind has traveled past the weather station within a given time period. The total Wind Run is reported in the daily data.
    Vapor Pressure:   The vapor pressure of the atmosphere is the partial pressure exerted by atmospheric water vapor. It is a good indicator of the humidity of the atmosphere and is calculated from measured relative humidity and air temperature data. Hourly, daily, and monthly data are available.
    Dew Point Temperature:   Dew point temperature is the temperature to which the atmosphere must be cooled, at constant pressure and water vapor content, in order to reach saturation. It is calculated from vapor pressure (relative humidity) and air temperature data. Hourly, daily, and monthly dew point temperature data are available.
  • Report Types
    CIMIS reference evapotranspiration (ETo) data is provided to you from two sources; Spatial and Station data. Spatial data is processed using satellite imagery and interpolated station data. Spatial ETo is reported daily – more detail is provided at the end of the following report description. Station data is processed directly from ground based reference sites specifically designed to provide data representative of the surrounding irrigated area. All CIMIS data is in Pacific Standard Time (PST). The following report type descriptions provide more detail.

    Station Reports available prior to registering and Logging in

    Prior to registering, limited access to CIMIS data is available. Limited Hourly, Monthly, and Daily Reports are available in Web Report format and in English or Metric units. For more data and selection options, you would need to register and log in.

    Limited Hourly Reports:   Limited Hourly Reports provide hourly data from your choice of CIMIS stations for today and the past 7 days (updated hourly). They consist of 10 pre-determined sensors: ETo; precipitation; solar radiation; vapor pressure; air temperature; relative humidity; dew point; wind speed; wind direction; and soil temperature.

    All Hourly Report data is the sum or average (depending on the weather parameter) of the previous hour’s 60 minute-by-minute readings. Some values are calculated by the datalogger and others are calculated by the CIMIS computer in Sacramento.
    Limited Daily Reports:   Limited Daily Reports provide Daily ETo and weather data for the past 7 days, ending with yesterday’s date. They consist of 14 pre-determined sensors: ETo; precipitation; solar radiation; average vapor pressure; maximum, minimum, and average air temperatures; maximum, minimum, and average relative humidities; dew point; average wind speed; wind run; and average soil temperature.

    All Daily Report data is the sum or average of the previously calculated hourly values. Or, it may be derived from the sum or average of 1440 minute-by-minute readings, depending on the weather parameter.
    Limited Monthly Reports:   Limited Monthly Reports provide monthly data for the past year, ending with the previous month. They consist of 13 pre-determined sensors: total ETo; total precipitation; average solar radiation; average vapor pressure; average maximum, average minimum, and average air temperatures; average maximum, average minimum, and average relative humidities; average dew point; average wind speed; and average soil temperature.

    All Monthly Report data is the sum or average (depending on weather parameter) of daily data for the whole month.
    FTP Reports:   Accessed from a link under the DATA navigation bar, these reports are for those interested in automatically downloading hourly and daily CIMIS station data or accessing all available historical data. This data is stored as CSV files in English and Metric units. Select DATA and click on the FTP Reports link to open the FTP site, then open the readme-ftp.txt file to learn more details.

    Station Reports available after Logging in

    Log in to access unlimited Hourly, Daily, Daily ETo Variance, Monthly, and Monthly Average ETo reports with full selection capabilities. Reports are available in several data formats and in English or Metric units. You may choose date ranges for data from one or multiple stations and by zip code. Historical data from “Inactive” or discontinued stations can also be selected.

    Hourly Report:   When logged in, Hourly Reports include full selection capabilities, with additional checkboxes for sensors and hours of interest. Along with the 10 predetermined (or default) sensors referred to above under Limited Hourly Reports, Hourly Reports provide data for 7 additional sensors, including: net radiation, resultant wind speed, standard deviation of wind direction, Penman-Monteith ETo, Penman-Monteith ETr, and two experimental sensors. The date range for data includes today’s hours. Some stations have data beginning in June of 1982.
    Daily Report:   Daily Report adds more sensors to the default available prior to logging in. By checking the box for sensors, you may access Daily Report’s 18 additional sensors, including: net radiation; maximum and minimum vapor pressures; eight wind rose values NNE, ENE, ESE, SSE, SSW, WSW, WNW, NNW; maximum and minimum soil temperatures; Penman-Monteith ETo and ETr; battery voltage, and two experimental sensors. The date range available includes data up to yesterday.
    Daily ETo Variance Report:   This report provides a comparative report of ETo variance for selected CIMIS stations. Retrieve the Target Year ETo, Previous Year ETo, Average ETo, and the percent difference (target vs average). The date range available includes data up to yesterday.
    Monthly Report:   This report provides Monthly ETo and weather data from CIMIS stations. The date range available includes data up to last month.
    Monthly Average ETo Report:   This report provides long-term averages of monthly ETo for selected CIMIS stations. A minimum of 5 years of data is needed to calculate Monthly Average ETo. Stations with less than 5 years of data use values from nearby stations with similar microclimates. Note: This calculation includes no date ranges because Monthly Average ETo is an average of all a station's historical data.

    Additional Reports available after Logging in

    Entering your ID (email) and password will also allow access to My Reports, Preferences, Spatial Report, and Schedule Spatial Report. If you don’t have an account, you may click on the link above to register. Note: Access to the CIMIS database may time out if there is no activity for 20 minutes.

    My Reports:   Accessed from a link under the DATA navigation bar, this area allows station data reports to be customized and scheduled for email delivery. Quick Reports are based on your preferences and lists of stations. Click on the Quick Report "List" links to execute Hourly, Daily, Daily ETo Variance, Monthly, and Monthly Average ETo reports. Custom Reports are based on customized preferences under the "Edit" links. There you may also select station data reports and schedule their delivery via email.
    Spatial Report:   Found under the SPATIAL navigation bar, this Spatial report provides daily ETo and Solar Radiation data at a 2 km resolution. Spatial data ranges from 2/20/2003 to yesterday's date. Reports are available in several data formats and in English or Metric units. You may also specify zip codes, map coordinate points, or data search by address.
    Schedule Spatial Report:   Also under the SPATIAL navigation bar, Schedule Spatial report provides the option to deliver daily ETo and Solar Radiation data to your email inbox. Data locations correspond to saved zip codes or to the saved coordinate list.

DWR Logo The following sections feature CIMIS-related publications for your reference. Note that some resources may no longer be current. Sections include the following: CIMIS Brochures and Publications, Drought Tips, UC Publications, Water Conservation News Articles, California Agricultural Technology Institute Articles, and Other Published Articles. Click on the “V” to the right of the section header to access the section.

  • CIMIS Brochures and Publications
    These publications were produced and published by CIMIS staff at the California Department of Water Resources. Be aware that contact information and other information in these publications are dated material. Please contact us for more details or if you need one of our publications that is not listed.

    Id                       Publication Name                                                                         How to get a Copy

    1   CIMIS Quality Data for Efficient Irrigation (2016)   View PDF Document
    2   Getting Started with CIMIS (2016)   View PDF Document
    3   Spatial CIMIS (2016)   View PDF Document
    4   Irrigation Scheduling Using CIMIS (2016)   View PDF Document
    5   CIMIS Station Siting (2016)   View PDF Document
    101   Agricultural Resource Book (2000)   View PDF Document
    102   Urban Resource Book (2000)   View PDF Document
    103   CIMIS Alert (1997)   View PDF Document
    104   CIMIS Evapotranspiration Zones (2012)   View PDF Document
    105   CIMIS Brochure (2010)   View PDF Document
    106   "How Much Water…" Crop Coefficients Brochure (2000)   View PDF Document
    110   Technical Elements of CIMIS (1998)   View PDF Document
  • Drought Tips
    Drought Tips These publications were developed as a cooperative effort between the following: the California Department of Water Resources; the University of California, Davis; the United States Department of Agriculture; and the Bureau of Reclamation Mid Pacific Region. Most of these publications deal with the effects of drought and methods to mitigate those effects.

    Id                             Publication Name                                                                   How to get a Copy

    92-09   Managing Irrigation in Fruit and Nut Trees During Drought (1992)   View PDF Document
    92-16   Leaching (1993)   View PDF Document
    92-17   Water Quality Guidelines for Vegetable and Row Crops (1993)   View PDF Document
    92-19   Water Quality Guidelines for Trees and Vines (1992)   View PDF Document
    92-20   Water Balance Irrigation Scheduling Using CIMIS ETo (1993)   View PDF Document
    92-21   Leaching Under Saline Shallow Water Tables (1993)   View PDF Document
    92-23   Furrow Irrigation (1993)   View PDF Document
    92-24   Coping With Declining Groundwater Levels (1992)   View PDF Document
    92-25   Sprinkler Irrigation (1993)   View PDF Document
    92-27   Using Shallow Ground Water for Crop Production (1992)   View PDF Document
    92-29   Irrigation Water Management Made Simple (1993)   View PDF Document
    92-32   Maintaining Water Quality for Irrigated Agriculture Under Drought Conditions (1992)   View PDF Document
    92-33   Reclaiming Sodic and Saline/Sodic Soils (1993)   View PDF Document
    92-34   Citrus Irrigation Scheduling During a Drought (1992)   View PDF Document
    92-35   Drought Tactics for Apricots (1993)   View PDF Document
    92-38   Field Use of Tensiometers (1992)   View PDF Document
    92-43   Deciding How Much to Plant During A Drought (1992)   View PDF Document
    92-44   North Coast Crop Coefficients for Field and Vegetable Crops (1992)   View PDF Document
    92-45   Central Coast Crop Coefficients for Field and Vegetable Crops (1992)   View PDF Document
    92-46   Sacramento Valley Evapotranspiration and Crop Coefficients for Field Crops (1992)   View PDF Document
    92-48   Crop Coefficients for Field, Vegetable, and Strawberry Crops: South Coast Inland Valleys and Coastal valleys and Plains (1992)   View PDF Document
    92-52   Irrigating Up Crops Efficiently With Sprinklers (1993)   View PDF Document
    92-56   How Much Water Are You Applying With Your Low Volume Irrigation System? (1992)   View PDF Document
  • UC Publications
    Picture of a crop being watered These Water and Irrigation Management Series publications are produced by the UC Cooperative Extensions. Copies of these publications can be purchased from the University of California Agriculture and Natural Resources (ANR) Catalog by contacting them at the address or links below.

    Please be sure to include the "Publication Name" and the "Leaflet Id" in your request.

    UC ANR Communications Services
    1301 S. 46th Street
    Building 478 - MC 3580
    Richmond, CA 94804
    (800) 994-8849

    Find the online Publication Catalog at
    For questions regarding shipping costs and tax, please order through the UC ANR website or contact Mary Allen Crowley at

    Id                             Publication Name                                                                   How to get a Copy

    21199   Basic Irrigation Scheduling (1981)   View PDF Document
    21426   Determining Daily Reference Evapotranspiration (ETo) (1995)   View PDF Document
    21380   Does Drip (and Other Low-Flow) Irrigation Save Water? (1987)   View PDF Document
    21259   Drip Irrigation Management (1992)   View PDF Document
    21453   Drought Irrigation Strategies for Deciduous Orchards (1989)   View PDF Document
    21454   Irrigation Scheduling: A Guide for Efficient On-farm Water Management (1989)   View PDF Document
    21427   Using Reference Evapotranspiration (ETo) and Crop Coefficients to Estimate Crop Evapotranspiration (ETc) for Agronomic Crops, Grasses, and Vegetables (1994)   View PDF Document
    21428   Using Reference Evapotranspiration (ETo) and Crop Coefficients to Estimate Crop Evapotranspiration (ETc) for Trees and Vines (1989)   View PDF Document
    3375   Agricultural Salinity and Drainage (2006)   ANR Catalog Link
    3377   Irrigation Pumping Plants (Rev. 2000)   ANR Catalog Link
    3378   Micro-irrigation of Trees and Vines (Rev. 1996)   ANR Catalog Link
    3380   Surge Irrigation (Rev. 1998)   ANR Catalog Link
  • California Agricultural Technology Institute Articles
    These articles were written by CIMIS staff for publication in the “Update” newsletter. Update is a quarterly publication of the California Agricultural Technology Institute at the College of Agricultural Sciences and Technology, California State University, Fresno. The actual CATI Update website is located at:

    Uses of CIMIS data in landscape irrigation scheduling (Spring 2007)   View PDF Document
    Efforts under way to mitigate spatial ETo data gaps (Fall 2006)   View PDF Document
    CIMIS data quality control revisited: temp and rel hum (Spring 2006)   View PDF Document
    Irrigation scheduling using reference evapotranspiration April 2005)   View PDF Document
    Net radiation estimation method performing well (January 2005)   View PDF Document
    CIMIS data use on the rise: New users welcomed (July 2004)   View PDF Document
    Outreach activities planned by CIMIS and UCD Extension (January 2004)   View PDF Document
    CIMIS Data Quality Control Procedures and Uses (July,2003)   View PDF Document
    Installing a new CIMIS weather station (January, 2003)   View PDF Document
    Selecting a CIMIS Weather Station for Your Area (October, 2002)   View PDF Document
  • Other Published Articles
    These articles were compiled from various sources by CIMIS staff for the benefit of CIMIS data users. If you have an article that you think would benefit CIMIS data users, please feel free to Contact Us.
    Acceptance of your article is subject to review by DWR staff.

    Daily reference evapotranspiration for California using satellite imagery and weather station measurement interpolation (October 2007 – Civil Engineering and Environmental Systems)   View PDF Document
    Quantitative Irrigation Scheduling is Simple and Does Work (April, 2003)   View PDF Document
    Statistical Control Charts for Quality Control of Weather Data for Reference Evapotranspiration Estimation (for more information, see December 2004 – Acta Horticulturae)   View PDF Document
    State Weather Stations to Help Water Users Irrigate Efficiently (December 2002 – Tehachapi News)   View PDF Document
    Helping Californians Irrigate Efficiently (Fall 2002 – DWR People)   View PDF Document
    Role of Technology in Irrigation Advisory Services: The CIMIS Experience (July 2002 – FAO/ICID)   View PDF Document
    Publicly Funded Weather Database Benefits Users Statewide (May-June 2000 – California Agriculture)   View PDF Document
    Evapotranspiration and Crop Requirements (January 1999 – DWR Water Facts)   View PDF Document
Many growers and landscape managers in California hire irrigation consultants to help with irrigation scheduling. They are hired to advise the grower or manager on when to irrigate and how much water to apply throughout the irrigation season. Consultants can also be hired to work with an individual for a specified term to train the individual to schedule irrigations using the consultants' computer programs (purchased or leased from the consultant).

Following is a list of consultants in California who offer water budget irrigation scheduling services. This list is not exhaustive. Please note that DWR is not endorsing the products listed on this page. Any consultant who offers water budget irrigation scheduling services can be added to this list by contacting CIMIS at:

Periodic review will purge any consultants with invalid contact information.

Ag Moisture Inc.
Robert Kent
39421 Road 36
Kingsburg, CA 93631
p (559) 906-1131
f (559) 897-2112
Ag-Water Management
Andy Hensel
6702 Day Dream Ct.
Bakersfield, CA 93312
p (559) 281-5555
Agri-Valley Consulting
Chris Morgner
P.O. Box 34081
Merced, CA 95344
p (209) 722-7665
f (209) 722-4370
Farouk Hassan Ph.D
P.O. Box 5632
Fresno, CA 93755
p (559) 224-1618
f (559) 348-0721
Bahman Sheikh, Water Reuse Consulting
Bahman Sheikh PhD, PE
3524 22nd Street
San Francisco, CA 94114
p (415) 695-1178
m (415) 990-9980
f (415) 648-3765
California AgQuest Consulting
Ron Brase
4545 N. Brawley Avenue
Fresno, CA 93722
p (559) 275-8095
f (559) 275-5301
California H2orticulture Services
Michael Johnson
2345 17th Avenue
Santa Cruz, CA 95062
p (831) 325-3376
Coastal Viticultural Consultants, Inc.
Bryan Rahn
1575 Deer Park Rd.
Angwin, CA 94508
p (707) 965-3700
f (707) 965-3737
Crop Care Associates, Inc.
Robert Gallagher
851 Napa Valley Corporate Way, Suite E
Napa, CA 94558
p (707) 258-2998
f (707) 258-2163
1432 Abbott Street
Salinas, CA 93901
p (831) 759-7377
m (831) 214-3690
Del Contes Landscaping Inc.
Del Conte
41900 Boscell Road.
Fremont, CA 94538
p (510) 353-3060
m (510) 353-3060
f (510) 353-6036
Dellavalle Laboratory, Inc.
Peggy Miller
1910 W. McKinley, Suite 110
Fresno, CA 93728
p (559) 233-6129
Dendron Landscape Management Consultants
Richard Reasoner
P.O. Box 855
Stinson Beach, CA 94970
p (415) 868-0479
f (415) 868-0278
Dickson Associates, Inc.
Marty Dickson ASIC
P.O. Box 415
Palo Cedro, CA 96073
p (530) 547-5515
f (530) 547-5513
430 Mesa Road
Nipomo, CA 93444
p (805) 748-7125
Fruition Sciences, Inc.
Virginie Scoarnec
5235 Shattuck Avenue, Suite 2
Oakland, CA 94609
p (510) 409-8854
f (888) 295-5187
Gardeners Guild, Inc.
Brian O'Hara
2780 Goodrick Ave.
Richmond, CA 94801
p (510) 439-3700
f (510) 439-3344
Green Leaf Mapping Control Systems
David McLeroy President
PO Box 2550
Cupertino, CA 95015
p (408) 257-2221
f (408) 257-2271
Jarald Davidson
1770 Serenity Way
Chico, CA 95928
p (530) 893-4520
f (530) 893-1342
Irrigation Consultation Evaluation (ICE)
Mike Connor CLIA
1203 Champion Oaks Drive
Roseville, CA 95661
p (916) 772-2226
f (916) 772-2226
Irrigation Essentials
John Ossa CID, CLIA, CLP
775 E. Blithedale Ave. #545
Mill Valley, CA 94941
p (415) 378-8404
Irrigation Matters
Pat Biddy
3233 S. I Street
Tulare, CA 93274
p (559) 686-5115
m (559) 708-3907
f (559) 686-5294
ISC Group, Inc.
Ivy Munion
340 Church Street
Livermore, CA 94550
p (925) 371-8230
Jacobsen Pacific SMM, Inc.
Erik Jacobsen President
4181 Brew Master Drive, Suite 4
Ceres, CA 95307
p (209) 541-1044
m (209) 480-5002
f (209) 541-1195
James D. Eddy Associates Irrigation Design Engineers
James Eddy
P.O. Box 2291
Danville, CA 94526
p (925) 867-3339
f (925) 242-5807
JMLord Inc.
JM Lord
267 N. Fulton
Fresno, CA 93701
p (559) 268-9755
f (559) 486-6504
JVB Consulting
Brock Meyer
543 Hudson Ct.
Davis, CA 95616
p (530) 219-3236
f (530) 758-2738
4969 E. Clinton Way, Suite 102
Fresno, CA 93727
p (559) 549-6506
m (559) 483-9508
Pacific Agronomics, Inc.
J Kornoff
3402 W. Holland Ave. #101
Fresno, CA 93722
p (559) 276-0401
f (559) 272-9363
Pacific Water Management Inc.
13625 Paseo Terrano
Salinas, CA 93908
p (831) 235-2576
f (831) 484-5631
Phytosphere Research
Ted Swiecki Ph.D.
1027 Davis Street
Vacaville, CA 95687
p (707) 452-8735
f (707) 452-8735
Precise Landscape Water Conservation, Inc.
Bill Kabaker
P.O. Box 5919
Sherman Oaks, CA 91413
p (866) 554-2925
m (818) 203-2935
Precision Irrigation Management Consulting
Lisa Mellor
P.O. Box 23
Linden, CA 95236
p (209) 482-4398
f (209) 887-1004
Premiere Viticultural Services, Inc.
Garrett Buckland
1427 Jefferson Street, Suite D
Napa, CA 94559
p (707) 261-8750
f (707) 255-2044
Progressive Viticulture
Stan Grant
P.O. Box 2134
Turlock, CA 95381
p (209) 669-7656
m (209) 614-2565
f (209) 669-7656
Rain for Rent
Dave Haas
P.O. Box 1968
Salinas, CA 93902
p (831) 422-7813
f (831) 422-0218
Russell D. Mitchell and Associates, Inc.
Russell Mitchell
2760 Camino Diablo
Walnut Creek, CA 94597
p (925) 939-3985
f (925) 932-5671
Scaliter Irrigation Engineering, Inc.
Dan Scaliter
902 Aaron Drive
Redlands, CA 92374
p (909) 794-5811
f (909) 794-5873
SECO Landscapes
Will Johnson
4385-A Twain Avenue
San Diego, CA 92120
p (619) 917-7326
Specialized Landscape Management Services, Inc. (SLM)
Rene Emeterio CLIA, CLT, CWM
P.O. Box 630002
Simi Valley, CA 93063
p (805) 520-7590
m (805) 823-5603
f (805) 520-7592
Spot Water Management, Inc.
Andy Slack
1272 Lincoln Avenue
San Jose, CA 95125
p (408) 288-8153
f (408) 288-8156
Wade Landscape
Robert Wade
4540 Campus Drive, Suite 100
Newport Beach, CA 92660
p (949) 494-2130
f (949) 252-5319
Water Management Group
Geza Kiss
2200 Business Way, Suite 100
Riverside, CA 92501
p (909) 788-8497
f (909) 788-8538
Wateraware, LLC
Scott Mcgilvray
101 Cooper St. Suite 219
Santa Cruz, CA 95060
p (831) 524-0144
6468 S. Butte Avenue
Tempe, AZ 85283
p (602) 463-5072
806 Brookwood Way
Chico, CA 95926
p (530) 864-2454
f (530) 893-0115
P.O. Box 61
Saratoga, CA 95071
p (408) 867-2444
Western Water Features, Inc.
Aaron Turner
5088 Hillsdale Circle
El Dorado Hills, CA 95762
p (916) 517-6847
Yamasaki Landscape Architecture
Jeff Ambrosia
1223 High Street
Auburn, CA 95603
p (530) 885-0040
m (530) 886-4068
There are many computer programs available to help growers and landscape managers schedule irrigations. Following is a list of available irrigation scheduling computer programs and their capabilities. This list is not exhaustive. Please note that DWR is not endorsing the products listed on this page. Anyone who has irrigation scheduling software available to the public can be added to this list by contacting CIMIS at:

Periodic review will purge any product for which we cannot contact the vendor.


1949 5th Street, Suite 101
Davis, CA 956 16
p 530-753-1458
f 530-753-1054
S Grove


University of California-Davis
Davis, CA 956 16
p 530-752-4628
f 530-752-1552
Rick Snyder


1432 Abbott Street
Salinas, CA 93901
p 831-759-7377
Michael Cahn


5235 Shattuck Avenue, Suite 2
Oakland, CA 946 09
p 510-409-8854
f 888-295-5187
Virginie Scoarnec


P.O. Box 6266
North Logan, UT 843 41
p 435-755-0400
f 435-755-0415
Steven Moore


25740 Century Oaks Blvd
Hockley, TX 774 47
p 936-372-9884


1 Grand Avenue
California State Polytechnic University
San Luis Obispo, CA 934 07
p 559-229-2195
f 559-229-9348
CL Norris


2686 Velarde Drive
Thousand Oaks, CA 913 60
p 805-499-9689


1427 Jefferson Street, Suite D
Napa, CA 945 59
p 707-261-8750
f 707-255-2044
Garrett Buckland


1141 W. Shaw Ave.
Fresno, CA 937 11
p 888-882-7873
f 877-752-6717


Lucas Lane
Stittsville, ON K2S 1S
p 613-831-7027
Peter Pharastus

Tiger Jill

2377 West Shaw - Suite #205
Fresno, CA 937 11
p 559-229-2195
f 559-229-9348
Udi Sosnik

True ISM

3262 Penryn Road, Suite 100
Loomis, CA 956 50
p 916-577-1470
Kent Johnson


California State University-Fresno
5370 North Chestnut Avenue, M/S OS 18
Fresno, CA 937 40
p 559-278-2066
f 559-278-6033
Steve O

Wingman Irrigation Scheduling

3233 S. I Street
Tulare, CA 93274
p 559-708-3907
Pat Biddy

Yara North America, Inc.

100 North Tampa Street, Suite 3200
Tampa, FL 33602
p 916-390-2999
Scott Warr