This ET_Idaho web site provides estimates of Evapotranspiration (ET), net irrigation requirement (NIR), and effective precipitation supporting transpiration and evaporation (PEff) estimates for areas in Idaho. These calculations and web site were produced in 2007 and were updated in 2009. ET calculation procedures employ a modern reference equation (ASCE standardized Penman-Monteith method) and a modern procedure to calculate crop coefficients that considers the impact of surface wetting by irrigation and precipitation on total evaporation from the soil surface. ET is provided for daily, monthly, and annual timesteps for 125 weather station locations across Idaho. In addition to ET and NIR estimates for agricultural crops grown in Idaho, ET estimates are available for a number of native plant systems (wetlands, rangelands, and riparian areas) and open water surfaces. The ET and NIR estimates are intended for use in design and management of irrigation systems, for water rights management and consumptive water right transfers, and for hydrologic studies. ET estimates are available for all times during the calendar year to provide information for land application design, operation, and management of waste streams from agriculture, food processing and other sources during the nongrowing periods.

These dynamic web pages allow you to access historical ET data for the State of Idaho at various locations. Currently, the data are based on 109 NWS cooperative weather stations and 16 AgriMet stations located in predominately agricultural areas through out the state.

Find and explore the summary data for stations and land covers:
Click on this link to locate stations by county or Please select a station from the following list: AgriMet -- Aberdeen NWS -- Aberdeen Experiment Station AgriMet -- Afton NWS -- American Falls 1 SW NWS -- Anderson Dam NWS -- Arbon 2 NW NWS -- Arco NWS -- Arrowrock Dam NWS -- Ashton AgriMet -- Ashton NWS -- Bayview Model Basin NWS -- Blackfoot NWS -- Bliss NWS -- Boise 7 N NWS -- Boise WSFO Airport NWS -- Bonners Ferry NWS -- Brownlee Dam NWS -- Bruneau NWS -- Buhl NWS -- Burley FAA AP NWS -- Cabinet Gorge NWS -- Caldwell NWS -- Cambridge NWS -- Cascade 1 NW NWS -- Castleford 2 N NWS -- Challis NWS -- Coeur d'Alene 1 E NWS -- Cottonwood NWS -- Council NWS -- Craters of the Moon NWS -- Deer Flat Dam NWS -- Driggs NWS -- Dubois Experiment Station NWS -- Dworshak Fish Hatchery NWS -- Elk City NWS -- Elk River 1 S NWS -- Emmett 2 E NWS -- Fairfield AgriMet -- Fairfield AgriMet -- Fort Hall NWS -- Fort Hall Indian Agency NWS -- Galena NWS -- Garden Valley RS NWS -- Glenns Ferry AgriMet -- Glenns Ferry NWS -- Grace NWS -- Grand View AgriMet -- Grand View NWS -- Grangeville NWS -- Grasmere NWS -- Hagerman 2 SW NWS -- Hailey Ranger Stn NWS -- Hamer 4 NW NWS -- Hazelton NWS -- Hill City NWS -- Hollister NWS -- Howe NWS -- Idaho City NWS -- Idaho Falls 16 SE NWS -- Idaho Falls 46 W NWS -- Idaho Falls FAA Arpt NWS -- Island Park NWS -- Jerome NWS -- Kellogg AgriMet -- Kettle Butte NWS -- Kilgore NWS -- Kooskia NWS -- Kuna NWS -- Leadore 2 NWS -- Lewiston WB AP NWS -- Lifton Pumping Stn NWS -- Lowman NWS -- Mackay Ranger Stn NWS -- Magic Dam NWS -- Malad NWS -- Malad City AgriMet -- Malta NWS -- Malta 1 NE NWS -- May NWS -- McCall NWS -- McCammon NWS -- Minidoka Dam AgriMet -- Monteview NWS -- Montpelier NWS -- Moscow - Univ of Idaho NWS -- Mountain Home 1 W AgriMet -- Nampa NWS -- New Meadows Ranger Stn NWS -- Nezperce NWS -- Oakley NWS -- Ola NWS -- Orofino AgriMet -- Parma NWS -- Parma Experiment Station NWS -- Payette NWS -- Picabo AgriMet -- Picabo NWS -- Plummer 3 WSW NWS -- Pocatello WB AP NWS -- Porthill NWS -- Potlatch 3 NNE NWS -- Preston 3 NE AgriMet -- Rexburg NWS -- Rexburg Ricks College NWS -- Reynolds NWS -- Richfield NWS -- Riggins Ranger Stn NWS -- Rupert AgriMet -- Rupert NWS -- Saint Maries NWS -- Salmon NWS -- Sandpoint KSPT NWS -- Shoshone NWS -- Soda Springs NWS -- St Anthony NWS -- Stanley NWS -- Strevell CAA Airport NWS -- Swan Valley 1 W NWS -- Tetonia Expermint Stn NWS -- Three Creek AgriMet -- Twin Falls NWS -- Twin Falls 2 NNE NWS -- Twin Falls 3 SE NWS -- Twin Falls WSO NWS -- Weiser
Explore annual and monthly trends in reference evapotranspiration and precipitation for all the ETIdaho stations by following the hot links below.
Annual Trends		Monthly Trends

Techincal Reports and other information:
A pdf copy of the 2007 report submitted to IDWR, Evapotranspiration and Consumptive Irrigation Water Requirements for Idaho, Research Technical Completion Report including the 2009 supplement is available for download here. The 2009 supplemental report covers the modifications, changes, and enhancements in computing evapotranspiration and is located at the end of the report pdf.

These estimates for evapotranspiration, precipitation deficit, and effective precipitation superceed the previous versions of ET_Idaho web site (2007) and those published by Allen and Brockway (1983). For historical purposes those estimates have been archived and are available by special request.

Changes from the 2007 ET_Idaho Dataset:
Evapotranspiration and net irrigation water requirement estimates were produced by the University of Idaho in 2007 through December 2004. These estimates were recomputed in 2009 and updated through December 2008 in this supplement to the 2007 report. ET is provided for daily, monthly and annual timesteps for 125 weather station locations across Idaho for complete, available periods of record. Two stations were added to the 2009 calculations: Craters of the Moon (Coop station 102260, 1959-2008) and Howe (Coop station 104384, 1958-2008). Thirty year normals have been updated to the end of 2008 (if 2008 was an active year of data collection for the station). To support calculations of ET, the complete National Weather Service Cooperative station database for Idaho stations was re-downloaded from the National Climate Data Center (NCDC) site so that some previous 'holes' in daily time series were filled in for some stations.

Slight changes in the logic of computing precipitation deficit were implemented in the 2009 update. The partitioning of evaporation into that supported by precipitation and by irrigation was modified to better distribute evaporation when both irrigation and a concurrent and/or recent rain event occured.

Minor coding errors discovered in the calculation routines were corrected in 2009. These coding errors included a correction to the statistics program to preclude calculated deep percolation from irrigation from going negative, but to allow effective precipitation to be negative on some days to account for delayed deep percolation of precipitation. In the primary ET calculation code, management of crop startup was modified to consistently calculate the correct estimated date of greenup or planting. Some resetting of variables at the start of a new crop was done and an error in estimating deep percolation from very shallow rooting depths in coarse soils was corrected (this did not occur often).

Additionally, effective precipitation for supporting transpiration and evaporation was partitioned for growing season, non-growing season, and annual time periods. For the annual time series, additional parameters have been included in the output to assist in the quantification of effective precipitation used in evapotranspiration during the growing and non-growing seasons. Also, estimates of non-growing season precipitation stored in the root zone and later used in the growing season are presented.

This work and report were prepared by the University of Idaho Research and Extension Center at Kimberly, Idaho under contract with the Idaho Department of Water Resources. Work was supported by funding from IDWR and the Idaho Agricultural Experiment Station and Idaho Engineering Experiment Station. The authors gratefully acknowledge the long-term evapotranspiration data collection and long-standing advice provided by Dr. James L. Wright, USDA-ARS Kimberly (ret.), the more than two decades of high quality agricultural weather data collection by the U.S. Bureau of Reclamation AgriMet system, and the very long-standing, routine data collection by the hundreds of cooperative weather station volunteers across the state who, for more than one-hundred years, have faithfully observed daily air temperature and precipitation.

The citation for the evapotranspiration data used from this site should be: Allen, Richard G. and Clarence W. Robison, 2009. Evapotranspiration and Consumptive Irrigation Water Requirements for Idaho: Supplement updating the Time Series through December 2008, Research Technical Completion Report, Kimberly Research and Extension Center, University of Idaho, Moscow, ID.

Questions regarding the data should be addressed to Clarence W. Robison or Richard G. Allen, University of Idaho, Kimberly Research and Extension Center, 3793 North 3600 East, Kimberly, ID 83341. Telephone (208)-423-6610

Copyright 2010, University of Idaho.