ET-IDWR

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: Aberdeen (ID) -- PN-AM Afton (WY) -- PN-AM Arco (ID) -- AM/INL Ashton (ID) -- PN-AM Baker Valley (OR) -- PN-AM Blackfeet (MT) -- GP-AM Blackfoot (ID) -- AM/INL BlueMtn (MT) -- RAWS Bonners Ferry Airport (ID) -- RAWS Bozeman (MT) -- GP-AM Cherry (WA) -- RAWS Corvallis (MT) -- PN-AM Deer Lodge (MT) -- PN-AM Dillon (MT) -- GP-AM Dworshak (ID) -- PN-AM Eureka (NV) -- PN-AM Fairfield (ID) -- PN-AM Fort Hall (ID) -- PN-AM Grace (ID) -- PN-AM Grand View (ID) -- PN-AM Greenfields (MT) -- GP-AM Greys Lake (ID) -- RAWS Hamer (ID) -- AM/INL Helena Valley (MT) -- GP-AM Howe (ID) -- AM/INL Idaho Falls (ID) -- AM/INL Imbler (OR) -- PN-AM Jefferson River Valley (MT) -- GP-AM Kettle Butte (ID) -- PN-AM Leadore Creek (ID) -- RAWS Lodgepole (ID) -- RAWS Malta (ID) -- PN-AM Minidoka (ID) -- AM/INL Monteview (ID) -- PN-AM Nampa (ID) -- PN-AM Ontario (OR) -- PN-AM Parma (ID) -- PN-AM Picabo (ID) -- PN-AM Pole Creek (ID) -- RAWS Preston (ID) -- PN-AM Priest Lake (ID) -- RAWS Quadrant (WY) -- RAWS Rathdrum Prairie (ID) -- PN-AM Rexburg (ID) -- PN-AM Richfield (ID) -- AM/INL Ririe (ID) -- PN-AM Roberts (ID) -- AM/INL Round Butte (MT) -- PN-AM Ruby River Valley (MT) -- GP-AM Rupert (ID) -- PN-AM Shields River Valley (MT) -- GP-AM Slate Creek (ID) -- RAWS St. Ignatius (MT) -- PN-AM Stanley RS (ID) -- RAWS Sugar City (ID) -- AM/INL Taber (ID) -- AM/INL Terreton (ID) -- AM/INL Teton River (MT) -- GP-AM Toston (MT) -- GP-AM Troy (MT) -- RAWS Twin Falls (ID) -- PN-AM White Sulphur Springs (MT) -- GP-AM Aberdeen Exp. Stn. (ID) -- NWS Alberton (MT) -- NWS American Falls 1SW (ID) -- NWS Anderson Dam (ID) -- NWS Arbon 2NW (ID) -- NWS Arco (ID) -- NWS Arrowrock Dam (ID) -- NWS Ashton (ID) -- NWS Avery RS #2 (ID) -- NWS Baker City (OR) -- NWS Bayview Model Basin (ID) -- NWS Big Sky 2WNW (MT) -- NWS Blackfoot (ID) -- NWS Bliss (ID) -- NWS Boise WSFO Airport (ID) -- NWS Bonners Ferry (ID) -- NWS Brownlee Dam (ID) -- NWS Bruneau (ID) -- NWS Buhl (ID) -- NWS Burley FAA AP (ID) -- NWS Cabinet Gorge (ID) -- NWS Caldwell (ID) -- NWS Cambridge (ID) -- NWS Cascade 1NW (ID) -- NWS Castleford 2N (ID) -- NWS Challis (ID) -- NWS Charleston (NV) -- NWS Chilly Barton Flat (ID) -- NWS Coeur d'Alene 1E (ID) -- NWS Cottonwood (ID) -- NWS Council (ID) -- NWS Craters of the Moon (ID) -- NWS Deadwood Dam (ID) -- NWS Deer Flat Dam (ID) -- NWS Dillon (MT) -- NWS Dixie (ID) -- NWS Driggs (ID) -- NWS Dubois Exp. Stn. (ID) -- NWS Dworshak Fish Hatchery (ID) -- NWS Elk City (ID) -- NWS Elk River 1S (ID) -- NWS Emmett 2E (ID) -- NWS Enterprize RS (OR) -- NWS Fairfield (ID) -- NWS Fenn RS (ID) -- NWS Fort Hall Indian Agency (ID) -- NWS Galena (ID) -- NWS Garden Valley RS (ID) -- NWS Glenns Ferry (ID) -- NWS Grace (ID) -- NWS Grand View (ID) -- NWS Grangeville (ID) -- NWS Grasmere (ID) -- NWS Grouse (ID) -- NWS Hagerman 2SW (ID) -- NWS Hailey RS (ID) -- NWS Halfway (OR) -- NWS Hamer 4NW (ID) -- NWS Haugan 1W (MT) -- NWS Hazelton (ID) -- NWS Headquarters (ID) -- NWS Hebgen Dam (MT) -- NWS Hill City (ID) -- NWS Hollister (ID) -- NWS Homedale (ID) -- NWS Howe (ID) -- NWS Idaho City (ID) -- NWS Idaho Falls 16SE (ID) -- NWS Idaho Falls 46W (ID) -- NWS Idaho Falls FAA Arpt (ID) -- NWS Island Park (ID) -- NWS Jackpot (NV) -- NWS Jerome (ID) -- NWS Kellogg (ID) -- NWS Ketchum RS (ID) -- NWS Kilgore (ID) -- NWS Kooskia (ID) -- NWS Kuna (ID) -- NWS Lakeview (MT) -- NWS Leadore 2 (ID) -- NWS Lewiston WB AP (ID) -- NWS Libby (MT) -- NWS Libby 32SSE (MT) -- NWS Lifton Pumping Stn (ID) -- NWS Logan 5SW (UT) -- NWS Logan USU (UT) -- NWS Lowman (ID) -- NWS Mackay RS (ID) -- NWS Magic Dam (ID) -- NWS Malad (ID) -- NWS Malta 1NE (ID) -- NWS May (ID) -- NWS McCall (ID) -- NWS McCammon (ID) -- NWS Minidoka Dam (ID) -- NWS Montpelier (ID) -- NWS Moscow - Univ of Idaho (ID) -- NWS Mountain Home 1W (ID) -- NWS NewMeadows RS (ID) -- NWS Newport (WA) -- NWS Nezperce 2E (ID) -- NWS Oakley (ID) -- NWS Ola (ID) -- NWS Orofino (ID) -- NWS Orovada (NV) -- NWS OwyheeDam (OR) -- NWS Palisades (ID) -- NWS Parma Exp. Stn. (ID) -- NWS Paul 1ENE (ID) -- NWS Payette (ID) -- NWS Picabo (ID) -- NWS Pierce RS (ID) -- NWS Plummer 3WSW (ID) -- NWS Pocatello WB AP (ID) -- NWS Porthill (ID) -- NWS Potlatch 3NNE (ID) -- NWS Preston 3NE (ID) -- NWS Priest River Exp.Stn (ID) -- NWS Pullman 2NW (WA) -- NWS Pullman/Moscow AP (WA) -- NWS Rexburg - Ricks College (ID) -- NWS Reynolds (ID) -- NWS Richfield (ID) -- NWS Richland (OR) -- NWS RigginsRS (ID) -- NWS Rosalia (WA) -- NWS Rosette (UT) -- NWS Rupert (ID) -- NWS Saint Maries (ID) -- NWS Salmon (ID) -- NWS Sandpoint KSPT (ID) -- NWS Shoshone (ID) -- NWS Soda Springs (ID) -- NWS St Anthony (ID) -- NWS Stanley (ID) -- NWS Stevensville (MT) -- NWS Strevell CAA Airport (ID) -- NWS Swan Valley 1W (ID) -- NWS Taylor Ranch (ID) -- NWS Tetonia Exp. Stn. (ID) -- NWS Three Creek (ID) -- NWS Troy (MT) -- NWS Twin Falls 2NNE (ID) -- NWS Twin Falls 3SE (ID) -- NWS Twin Falls WSO (ID) -- NWS Virgina City (MT) -- NWS Weiser (ID) -- NWS Western Ag Res Ctr (MT) -- NWS Winchester 1SE (ID) -- NWS Wisdom (MT) -- NWS

Dr. Rick Allen and Clarence Robison, researchers from the University of Idaho Kimberly Research and Extension Center, authored the 2007 dataset and report under contract with the Idaho Department of Water Resources (IDWR). Work was supported by funding from IDWR, the Idaho Agricultural Experiment Station, and the Idaho Engineering Experiment Station. IDWR periodically contracted with the University of Idaho to extend the time series. Allen and Robison made updates in 2009, 2012, 2017, and most recently in 2023. Each update provided opportunities for adding weather stations and improving the code. The entire time series was reanalyzed with each update, meaning that each update supersedes all previous updates. A summary of the updates is provided below. In 2020, with the retirement of Dr. Rick Allen on the horizon, IDWR contracted once more with the University to obtain an updated dataset and to in-house the knowledge to make independent updates in the future. The 2023 update is the result of that work. The 2023 update also adapted the United States Bureau of Reclamation's (USBR) Python ET-Demands model to match the Visual Basic 6 ET_Idaho model. The switch to ET-Demands was necessary because Microsoft no longer supports Visual Basic 6.

The ET_Idaho website was initially developed and maintained by Clarence Robison at the University of Idaho. To ensure the continued availability of the ET_Idaho-like data, IDWR created this website.

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. The 2016 update to ET_Idaho is covered in a supplemental report that is available for download here.

In 2009, the University of Idaho updated evapotranspiration and net irrigation water requirement estimates through 2008. These estimates were updated in 2012 through December 2010. In 2017, the estimates were again recomputed and updated through 2016. In 2023, the estimates were updated through 2021. The 2023 version provides data for daily, monthly, and annual timesteps for 208 weather stations across Idaho. Thirty-year normals have been updated to the end of 2021 (if 2021 was an active year of data collection for the station).

2009
Minor coding errors discovered in the calculation routines were corrected in 2009. These coding errors included a correction to the statistics program to prevent 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, the crop startup was modified to consistently calculate the 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).

2012
Slight changes in the logic of computing precipitation deficit were implemented in the 2012 update. The partitioning of evaporation into that supported by precipitation and by irrigation was modified to distribute evaporation better when both irrigation and a concurrent and/or recent rain event occurred. 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 were included in the output to assist in quantifying 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 were added.

2017
For the 2017 version, 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. The 2017 update also added additional stations surrounding Idaho in Oregon, Washington, Montana, Wyoming, Utah, and Nevada. Due to the abandonment of some COOP stations, some stations found in the earlier releases were not included in this release. Some COOP stations were supplemented with nearby stations (coop or automatic) to provide a more complete record.

2023
The 2023 update involved relatively minor changes to the United States Bureau of Reclamation's (USBR) ET-Demands model, which is a derivative of the ET_Idaho model, to better match the results from the original ET_Idaho model. After running ET-Demands with the same inputs as ET_Idaho, differences in time series of daily ET were noted and efforts were made to identify the computations in the ET-Demands code that produced the differing outputs. Some differences were due to improvements to the original ET_Idaho computations. In many cases, the differences create small discrepancies that have little impact on long-term statistics. The most significant difference is how missing weather data are filled. Subtle changes to the weather data cause changes to the starts and durations of Kc curves, to soil water balances, and to irrigation schedules. Changes to snow data impact ET by modifying the Kc curves by increasing albedo and increasing the energy to evaporate water from its solid state. Changes to snow data also change the cumulative GDD used to trigger the green-up of winter grains. Some of the changes to the 2023 version included the following:

• Missing air temperature and wind speed data were filled with the long-term DOY means in 2017 but were filled with the long-term monthly means in 2023.
• Missing snow data were filled with the long-term DOY mean in 2017, but in 2023, the snow depth was based on a minimum of 11 years of record for the DOY from which the median depth was selected. The median depth was set to zero if less than 26 mm. The median depths were smoothed with a 7-day running average. The running average is set to zero if less than 26 mm. If all seven days were missing snow cover information, the snow depth was set to the long-term mean snow depth for the day. If there were fewer than 11 years of data, the snow depth was filled with 0.
• Missing rain data were filled with the long-term DOY mean in 2017, but in 2023, they were set to 0 if the mean was less than 0.3 mm
• Winter wheat was not initialized during the first growing season in ET_Idaho, resulting in very low ET for the first year of the time series. Winter wheat was correctly initialized in the 2023 version.
• Alfalfa uses three different Kc curves: one for the pre-cutting period, another for mid-season cuttings, and a third leading up to the final cutting. The 2017 version incorrectly applied the final curve to mid-season cuttings. The 2023 data fix this error.
• Canola and Mustard were treated as rainfed in southern Idaho in the 2017 version, but they were modified to be irrigated in the 2023 version.

2024-10-16
We discovered that 54 weather stations had missing monthly 30-year statistics, and that those missing data prevented previously established uses of ETIdaho/ET-IDWR. ETIdaho did not contain any missing data because it only selected years for the 30-year statistics that were nearly guaranteed to be free of missing data. ET-IDWR only filters out years for the 30-year statistics if they have more than fifteen missing days. In the first 2023 version of ET-IDWR, monthly means were set to missing if there were four missing days in the month, and the 30-year means were set to missing if any month was missing. For example, if any January in the ~30 years selected for statistics contained more than 4 missing values then the 30-year mean for January would be set to missing. To fill the missing values while preserving the other values we reran the 30-year statistics but allowed up to 15 missing values in a month. Because only 15 missing values are allowed in a year this guarantees that every month will have valid data. There are still missing 3, 7, and 15-day moving window statistics but they are rare, and filling those missing values will be a task for the next major update to the data.

2025-11-05
New stations were added. The Preston, Grace, and Ririe Agrimet stations, and the Bonners Ferry Airport RAWS station.

PDef for water is now available and is calculated as ETact - P.

A PDef bug for rainfed stations/covers was fixed. In the last version of ET-IDWR (and in the last version of ET_Idaho), rainfed covers calculated PDef as actual ET minus effective precipitation (ETact - P_rz). During the growing season, this led to PDef being underestimated at rainfed sites because ETact is limited by precipitation. The code has been updated to match what is described in the ETIdaho documentation supplement for 2009, revised in 2011. Growing season PDef for rainfed covers is now correctly computed as potential ET minus effective precipitation (ETpot - P_rz).

RAWS stations use tipping-bucket rain gauges that aren't designed to accurately measure precipitation in the winter. Therefore, we opted to replace the RAWS station-reported precipitation with 800m PRISM daily precipitation.

Additional historical weather data were flagged for removal after manual review and may result in small shifts in statistics.

Previous versions of the code were written so that if planting or green-up didn't occur before day of year (DOY) 195 the growing season wouldn't start. For certain crops and stations, this resulted in years where no crop was ever simulated. We changed the logic to force the growing season to start on DOY 195 if it hadn't already started.

NWS stations do not measure wind speed, so they "borrow" monthly average wind speed from automatic weather stations. With this update, we changed the wind stations assigned to 10 NWS stations. These 10 stations had wind stations that were more than 75% closer than their old wind stations. Wind speed is an important factor in calculating all ET variables, so expect significant changes in ET at some of these stations.

Wind station changes:

• Blackfoot (ID) -- NWS, previous wind from Aberdeen (ID) -- PN-AM, new wind from Blackfoot (ID) -- AM/INL
• Bonners Ferry (ID) -- NWS, previous wind from Priest Lake (ID) -- RAWS, new wind from Bonners Ferry Airport (ID) -- RAWS
• Fort Hall Indian Agency (ID) -- NWS, previous wind from Aberdeen (ID) -- PN-AM, new wind from Fort Hall (ID) -- PN-AM
• Grace (ID) -- NWS, previous wind from Afton (WY) -- PN-AM, new wind from Grace (ID) -- PN-AM
• Hamer 4NW (ID) -- NWS, previous wind from Monteview (ID) -- PN-AM, new wind from Hamer (ID) -- AM/INL
• Howe (ID) -- NWS, previous wind from Monteview (ID) -- PN-AM, new wind from Howe (ID) -- AM/INL
• Idaho Falls FAA Arpt (ID) -- NWS, previous wind from Rexburg (ID) -- PN-AM, new wind from Idaho Falls (ID) -- AM/INL
• Preston 3NE (ID) -- NWS, previous wind from Logan USU, new wind from Preston (ID) -- PN-AM
• Richfield (ID) -- NWS, previous wind from Twin Falls (ID) -- PN-AM, new wind from Richfield (ID) -- AM/INL
• Alberton (MT) -- NWS, previous wind from Troy (MT) -- RAWS, new wind from Blue Mtn (MT) -- RAWS

The time series data will continue to be updated periodically by IDWR. Future versions will possibly use gridded weather data instead of weather station data. Gridded data offers several advantages, including complete spatial coverage of Idaho and temporal coverage back to 1979. GridMET is an example of a gridded weather dataset.