Water resources research
Water resources research
The water resources research team at University of Idaho's Kimberly Research and Extension Center is a national leader on consumption of water by irrigated agriculture and natural systems. The group also conducts research on water quality and hydrology. The METRIC platform for transforming satellite imagery into maps of water consumption and the REF-ET and ETIdaho systems for calculating reference crop ET and for reporting crop water requirements for the State of Idaho were created by the water resources research team. For irrigation water management issues, please visit irrigation water management.
Remote sensing of evapotranspiration
The generation of evapotranspiration maps using Landsat satellite images is based on METRIC (Mapping EvapoTranspiration at high Resolution and Internalized Calibration).
This process was initially funded in the early 2000s by the Idaho Department of Water Resources (IDWR). Since then, evapotranspiration maps for eastern southern Idaho have been generated for 1986, 1996, 2000, 2006, 2008, 2009, 2010, 2011, 2013, 2016, 2017 and 2018. We are currently finalizing "Near Real Time" METRIC processing for 2019 and processing 2020 in near real time. The finalized images/maps are available from the IDWR ET GIS website.
Additionally, we are working on generation of METRIC evapotranspiration maps for the Treasure Valley area (Boise to Fruitland) for select years to support IDWR and USGS Treasure Valley aquifer modeling project. Treasure Valley METRIC evapotranspiration maps have been completed for 1994, 2000, 2007 and 2015 which have been submitted to IDWR. We are currently working on Treasure Valley maps for 1987, 2010, 1997 and 2004. The process has also been applied at various locations throughout the United States and the world.
In 2009, the IDWR — University of Idaho partnership that applies METRIC-based ET in IDWR hydrology and water rights and operations was awarded the prestigious Innovations in American Government Award by the Ash Institute of the Kennedy School of American Governance of Harvard University.
An implementation of METRIC on the Google Earth Engine is known as EEFlux. EEFlux has been in development since 2012 by the University of Idaho, University of Nebraska and Desert Research Institute. EEFlux uses an automated calibration scheme to produce ET, ETrF and EToF images for single Landsat scenes. TIF files can be downloaded and processed by users to produce time-integrated monthly ET. The automation of calibration accuracy of the final product by about 5 to 15% as compared to hand calibration by trained and experienced personnel using METRIC processes. Provision is made on the EEFlux website to make adjustments to final ETrF images. More information is available on the EEFlux website https://eeflux-level1.appspot.com/.
Animations of ET in Idaho are available at: Evapotranspiration from Landsat which was produced by the NASA Goddard Space Flight Center.
A two-page Landsat specifications description sponsored by the Western States Water Council that advocates for a four-day Landsat revisit time is available: Essential specifications for Landsat — WSWC April 9, 2012 (pdf). A four-day revisit time can be accomplished by having four currently-designed Landsats in orbit at the same time, or by launching new Landsat satellites that have twice the path width as the current design. In 2017, the Landsat Science Team formulated future requirements for the Landsat program. A one-day Landsat revisit time would nearly guarantee the ability to consistently produce evapotranspiration images for the entire continental U.S.
Most of the continental U.S. requires 16 satellites for a clear image every 16 days, 70% of the time. This PowerPoint shows the impact of the number of satellites and probability of cloud-free images to produce cloud-free ET images at least once per 16 days or once per 32 days for the continental U.S. (ppt). An additional analysis for southern Idaho based on actual Landsat image collections over the past forty years summarizes the impacts of clouds on one versus two satellites for southern Idaho annual ET (pdf).
A NASA document (pdf) which describes an application of METRIC ET data in Idaho to help with a water rights disagreement can be viewed at https://landsat.gsfc.nasa.gov/wp-content/uploads/2014/08/Landsat_Improve_Life_Water.pdf.
Ref-ET: reference evapotranspiration calculator
Ref-ET is a Windows based software package that calculates reference evapotranspiration (ET). ET is defined as the amount of water that evaporates from vegetation (transpiration) and from the underlying soil. Reference evapotranspiration is defined as the ET that occurs from a standardized “reference” crop such as clipped grass or alfalfa. Common usage in the United States and elsewhere has been to use the two reference crops of clipped grass (cool season varieties) and full-cover alfalfa (lucerne).
The Ref-ET program provides standardized calculations of reference evapotranspiration for fifteen of the more common methods and equations that are currently in use in the United States and Europe. The calculations are based on the weather data measurements that are made available by the user.
The two primary purposes of Ref-ET are to:
- Provide standardized calculations of reference ET and other intermediate micro meteorological parameters that can be compared to calculations by other programs for error checking purposes.
- Read weather data from a wide range of data file types, data unit types and time steps.
The Ref-ET program includes commonly used algorithms and assumptions required in estimating reference ET. However, application of the Ref-ET program to various combinations or types of data may occasionally violate assumptions or may require extrapolation beyond endpoints of algorithms, resulting in incorrect ET and parameter estimates. Therefore the user of this software assumes all responsibility and reliability for accuracy and correctness of estimates.
Disclaimer: Neither the American Society of Civil Engineers, the United Nations Food and Agriculture Organization, University of Idaho, nor the author of Ref-ET (R.G. Allen) accept any liability for errors or incorrect results from the Ref-ET program nor any problems associated with installation of the software onto the user’s computer system.
All source code and executable code of this program is copyrighted by Richard G. Allen and University of Idaho.
Standardization of reference evapotranspiration
Evapotranspiration represents the loss of water from the earth’s surface through the combined processes of evaporation (from soil and plant surfaces) and plant transpiration (i.e. internal evaporation). Reference evapotranspiration is the rate at which readily available soil water is vaporized from vegetated surfaces.
This video presentation, History, intent and structure of reference ET standardization and its role in ET models, was given by R.G. Allen at the American Society of Agronomy Annual Meeting on Nov. 10, 2020.
The Environmental and Water Resources Institute (EWRI) of the American Society of Civil Engineers (ASCE) issued a report that defines a benchmark reference evapotranspiration equation that standardizes the calculation of reference evapotranspiration. The intent is to produce consistent calculations for reference evapotranspiration and to improve transferability of crop coefficients.
Additional resources:
- ASCE Standardized Reference Evapotranspiration Equation draft main report body without appendices —updated Sept. 2005 (pdf)
- ASCE Standardized Reference Evapotranspiration Equation report appendices link to ASCE-SREE-appendix (pdf)
- Issues, requirements and challenges in selecting and specifying a standardized ET equation (pdf)
- Conversion of right and Wright alfalfa-based crop coefficients (pdf)
- Comparison of cumulative evapotranspiration (pdf)
- Quality assessment and control of automated weather data (pdf)
Guidelines for computing crop water requirements
Evaporation and consumptive irrigation requirements for Idaho (Allen and Robison, 2006, rev. 2017), updated evapotranspiration (ET) and net irrigation requirement (NIR) estimates for areas in Idaho. New ET calculation procedures were employed including an updated reference equation. The results of the work and data sets are available at the ET-IDWR website and supersede those from Appendix E — Estimating Consumptive Irrigation Requirements for Crops in Idaho (Allen and Brockway, 1983).
Water quality monitoring
U of I water resources research team has been involved with water quality studies on the Snake River and surrounding watersheds since 1990. Besides monitoring the river, irrigation return flows, canal systems, springs, wells (groundwater), tributary and water quality improvement facilities (best management practices) sites have been sampled for various water quality parameters. The focus has been the collection of water quality data related to irrigation return flow sediment and nutrients and have been supported by the Twin Falls Canal Company, U.S. Bureau of Reclamation and U.S. Department of Agriculture. The monitoring data assists in documentation trends in water quality over time. The historical monitoring data is available online at https://data.kimberly.uidaho.edu/HITS and is typically updated after the irrigation season ends and data has been reviewed.
Food and agriculture organization publication 56
Reference evapotranspiration calculator
Ref-ET is a Windows based software package that calculates reference evapotranspiration.