WERA1022: Meteorological and Climate Data to Support ET-Based Irrigation Scheduling, Water Conservation, and Water Resources Management (from WDC18)

(Multistate Research Coordinating Committee and Information Exchange Group)

Status: Active

WERA1022: Meteorological and Climate Data to Support ET-Based Irrigation Scheduling, Water Conservation, and Water Resources Management (from WDC18)

Duration: 10/01/2017 to 09/30/2022

Administrative Advisor(s):

NIFA Reps:

Statement of Issues and Justification

Although the need for multistate coordination of irrigation water resources has always existed, recent droughts and a major population expansion in many western states has made this coordination even more imperative. Irrigated agricultural acreage is on the decline in many areas of the Western U.S., but it is still an important producer and the major user of water in most western states, where it is estimated that 90% of the freshwater drawn from well and surface sources is used for agriculture.

Irrigation scheduling models that have been developed to assist growers to estimate when and how much irrigation water to apply to their crops. Most, if not all, scheduling models use weather or climate data, which are commonly produced and disseminated by state or regional personnel. The data formats, however, vary by location, and local irrigation scheduling models only utilize local data. Data differences include time steps (hourly vs. daily), weather parameter order, and level of quality control. Clearly, there exists a need to coordinate weather data collection, storage formats, and data quality control in addition to sharing scheduling models.  Crop evapotranspiration (ETc) is commonly estimated by first calculating standardized reference evapotranspiration (ETref), which accounts for the weather influence on evaporative demand.

Then, the ETref is multiplied by a crop coefficient (Kc) factor to estimate ETc. The ASCE-EWRI committee developed unique equations to estimate ETref for a short reference canopy (ETo) and for a tall reference canopy (ETr). Both equations are modifications of a version of the Penman- Monteith equation (ASCE-EWRI, 2005, Allen et al. 1998). Because new equations are used for ETref, questions have arisen about the accuracy of existing Kc factors. It is desirable to standardize Kc development and to find methods to make Kc values more universally applicable. During the period of the recent WERA-202 coordinating committee, a methodology to convert Kc values for use with ETo and ETr was developed. However, Kc values also vary with the cli-mate, irrigation system, and irrigation frequency, so further research/coordination is needed. There exist many varying methods used regionally and from state to state to address ET-based irrigation scheduling.

Irrigation scheduling models vary farm-to-farm, state-to-state, and region-to-region. There is need to coordinate, discuss, and review these models to improve and standardize methodologies and to provide clientele with the best possible information for irrigation management. One ex-ample of the need for better irrigation scheduling information and methods is the Environmental Quality Incentive Program (EQIP) program offered through the USDA Natural Resource Conservation Service (NRCS). This program has begun providing cost-share money to producers to improve their irrigation water management. To be paid, the producers have to show documentation of irrigation water management for the entire growing season. This has created a demand for irrigation water management training for producers and NRCS staff. These demands have further increased the need for accurate crop specific water use estimates.


  1. Coordinate the documentation of crop coefficients used in irrigation scheduling.
    Comments: Coordinating documentation of crop coefficients across many different entities is a difficult process. Each network has a different format and method for utilizing crop charts as well as it's own nuances. The group will work together as a first step to publish the crop coefficients to a website with a description of use and any disclaimers. The group will then work to standardize the crop coefficients to a common format for ease of use.
  2. Coordinate efforts to promote adoption of improved irrigation scheduling technology, including computer models based on crop coefficients and ETref, remote sensing and instrumentation that will help producers more efficiently apply irrigation water.
    Comments: The group will include links to all known irrigation scheduling tools and related contacts on the website with the crop coefficients. Participants will work on promoting a website as well as their individual tools.
  3. Coordinate the development of quality control (QC) procedures for weather data used for irrigation scheduling.
    Comments: The website mentioned in objective 1 and 2 will also contain a QC component outlining each network's routine to include both data and field procedures. The group will work toward having a standardized document or set of procedures to include timing of calibrations and frequency of data QC.

Procedures and Activities

In this project, information sharing will occur mainly through the coordinating committee webpage. Any suggested changes to the coordinating committee webpage must be approved by both the Chair and Secretary, and the actual changes can only be made by the committee offi-cers.


Objective 1: Coordinate the documentation of crop coefficients used in irrigation scheduling:

(a) Develop a database on available crop coefficient data in the U.S., and especially in the Western U.S., including information on the method used to calculate ETref, the local climate, the time step used in the analysis, and the method used to determine the Kc curves (i.e., degree days, time, percent season, growth stage, etc.). This will involve assessment of the weather station design and siting, ETref calculation, data quality control, and ETc measurement. (b) Work with ASCE Kc task subcommittee on the development of a procedure for standardizing crop coefficient data.


Objective 2: Coordinate efforts to promote adoption of improved irrigation scheduling technology, including computer models based on crop coefficients and ETref, remote sensing and instrumentation that will help producers more efficiently apply irrigation water:

(a) Evaluate effectiveness of technology transfer delivery methods and programs, and document application of ET-based irrigation scheduling by agricultural producers. (b) Work with USDA-NRCS to provide and promote use of ET and irrigation scheduling information to producers.


Objective 3: Coordinate the development of quality control (QC) procedures for weather data used for irrigation scheduling.

(a) Cooperate with WERA-102 on developing standards for QC data in climate networks. Publish existing QC for climate networks in each participating state in a document available to all potential users. (b) Coordinate the development of estimation and interpolation programs to fill in missing data from climate networks, as irrigation scheduling programs typically do not run with missing data. (c) Coordinate with weather station system suppliers on the need for high quality, reliable equipment and to assist them in supplying their customers with appropriate training and instructional  materials.

Expected Outcomes and Impacts

  • Development and publication of methods for determining crop coefficients. The impacts of this standardization will be an increased ability to share information on crop water use across state and regional lines, resulting in increased water conservation.
  • Increased adoption of ET-based irrigation scheduling and other efficient irrigation technology. Target audiences will become more aware of and familiar with the technology and crop water needs. Water use efficiency will be increased, and limited irrigation water supplies will be better managed. Application of water use data will expand into the urban sector
  • Development and publication of quality control procedures that can be used to evaluate and improve weather data used for irrigation scheduling, resulting in improved irrigation scheduling and potentially an increase in yield per unit of irrigation water applied.

Projected Participation

View Appendix E: Participation

Educational Plan

Many of the participants serve on committees of ASABE, ASCE, Crop Consultants of America (CCA), and the Irrigation Association (IA). It is not possible for everyone to attend and keep abreast of all the activities being conducted by these organizations. One of the major activities of this committee will be to have a session at each meeting that conveys to the group the activities in these other organizations and coordinates the activities among these groups. Another purpose of this committee is the on-going education of its participants regarding the activities on the web connected with irrigation scheduling. Specifically, the new committee will conduct the following activities:

  1. Educational sessions at meetings about different aspects of irrigation scheduling material and software

  2. Development of effective documentation of irrigation scheduling information available through a new website with links to crop coefficients, irrigation scheduling tools and quality control procedures. The website will be promoted through network administrators, research extention agents and state/local officials.

  3. Dissemination of information through newsletters, faxes, press releases and magazine articles, presentations for end-users, including other media

  4. Development of short course information on irrigation scheduling using climate


The coordinating committee will have a Chair who is responsible for calling the annual meeting, preparing the agenda, Chairing the annual meeting, and obtaining approval of the previous meeting minutes. The Chair will form subcommittees to address the various objectives and tasks. The Secretary is responsible for writing the minutes and disseminating them for committee approval. In the annual meeting, the coordinating committee will elect a Chair and a Secretary for the following year. The term of the new Chair and Secretary begins within two months after the annual meeting when the previous Chair provides the annual meeting minutes to the new Chair.

Literature Cited

Allen, R. G, L.S. Pereira, D. Raes, and M. Smith. 1998. Crop evapotranspiration (guidelines for computing crop water requirements). United Nations FAO, Irrigation and Drainage Paper No. 56: Rome, Italy.

ASCE-EWRI. 2005. Eds: Allen, R.G., Walter, I.A., Elliott, R.L., Howell, T.A., Itenfisu, D., Jensen, M.E., Snyder, R.L. The ASCE Standardized Reference Evapotranspiration Equation. Reston, VA: American Society of Civil Engineers.


Land Grant Participating States/Institutions


Non Land Grant Participating States/Institutions

US Bureau of Reclamation, USDA-ARS/TX
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