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General Information

The IDWR ET Viewer allows users to find evapotranspiration (ET) datasets for Idaho, display them on a map and calculate ET and consumptive irrigation requirements (CIR) statistics for their area-of-interest. CIR is the amount of water required for consumptive use that is artificially applied to the soil. Seasonal CIR values do not account for the potential contribution of soil moisture accumulated during winter months. CIR is negative where precipitation exceeds evapotranspiration. Only seasonal CIR values are calculated. No monthly values are provided.
The ET datasets are developed using the METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration) satellite-based surface energy balance model developed by the University of Idaho . The input datasets are Landsat satellite data.

The ET Viewer has built-in tools to help you select an area using irrigation companies or water rights places of use. You can draw a polygon to define your own area-of-interest. Alternatively, you can select your area-of-interest, if it falls within the Eastern Snake Plain Aquifer, by using sets of "irrigated lands" polygons developed by the IDWR. This is explained below.

The ET Viewer uses Esri's ArcGIS Server to allow the user to locate their area-of-interest and compute the evapotranspiration (ET) and consumptive irrigation requirement (CIR) for that area. ET Statistics are computed using Esri's ArcGIS Zonal Statistics as Table geo-processing tool. Your area-of-interest is used (much like a "cookie cutter") to define the portion of the ET dataset on which the statistics are calculated.

The map, to the right, shows the outlines of the ET datasets. The datasets for the eastern part of the state are available for several of the years between 1986 and present, as reflected in the labels. The datasets for the west side of the state are limited to the years 2000 and 2015.


Initial Page

The home page of the ET Viewer gives you a brief description of METRIC. It also provides an overview of what the application does, in a very broad sense. The Landsat mosaic map shows the general orientation of Landsat paths and rows, in relation to the state of Idaho. It is an interactive map; you can select your area-of-interest from it. Click the "Help with Map" button for detailed help.

Find ET

The Find ET page gives you several ways to narrow your search for ET datasets. When you use one of these search-methods, select an item and click the "Search" button, a list of ET datasets which match your search criteria will be shown at the bottom of the page. With the exception of the Browse All ET Data option, the choice you make on this page will make fewer datasets available on the Details page.

For example, if your area-of-interest is entirely within the boundary of the Administrative Basin #37 (Big Wood River) you can select that basin, click the search button and be presented with a list of ET datasets which intersect with that basin. Note: If you select ET datasets by water right or irrigation company, only those ET datasets which completely contain the chosen irrigation entity or water right will be available in the list. You can use the Browse All ET Data option to make all of the ET datasets available for the next page of the application.

The results of the search may contain more than 100 datasets. Click on one of the ET Statistics links to use that dataset for calculations.


The Details page displays the selected ET dataset along with a background and any selected overlays, such as county boundaries, hydrography, etc. Note: If you experience a long wait-time when you initially load the Details page, select a different ET dataset from the drop-down list; wait until it loads, and then select the desired dataset.

Change ET Datasets

You may change ET datasets at any time by choosing a new ET layer from the drop-down list near the upper, right corner of the page.

Change Background Image (or other overlays)

You may add or change background images by clicking on the Change Background link. You can add/change other layers, such as administrative basins or ground water districts, as well. Note: The map is redrawn each time you change the background image or other layers. So, make those changes before you define your area-of-interest and calculate statistics.

Select a Method for Gathering Statistics

You may select an area for which to collect ET statistics by one of three methods. These three methods differ in two ways.
First, the model used to calculate statistics for Irrigation Entities uses a large cell-size when computing statistics because this yields faster results for large areas. The Water Rights and Select Area by Polygon methods — because they (usually) deal with smaller areas — use a one-meter-square cell-size. This makes for accurate calculations but, if the selected water right or digitized polygon is quite large, may take more than three minutes to complete.
Second, the Select Area by Polygon methods require the user to interact with the map in order to define their area-of-interest.

Select the tool you wish to use to define your area-of-interest by clicking the appropriate radio button.

Irrigation Entities

Select the irrigation district, canal company, etc. from the drop-down list. The map will zoom to the extent of that area and its boundary will be drawn on the map. Click the Get ET Statistics link to calculate the statistics.

Water Rights

Select the type of water right (right, permit, claim or recommendation). Enter the basin number, sequence number and suffix/version (if available). Click the Search link. Select the desired water use; the example shows a water right for “irrigation.” The map will zoom to the extent of that area and the boundary will be drawn on the map. Click the Get ET Statistics link to calculate the statistics.

Select Area by Polygon — Draw Polygon

Click the "Draw Polygon" button then click on the map to define the first point of your polygon. Continue to draw your polygon by clicking on the map at each point on the polygon. Double-click to finish the polygon (to draw a rectangle, click three points and then double-click the fourth one – the polygon will close on the initial point). After you double-click to close the polygon, the map will zoom to that area and the polygon will be redrawn on the map. Click the Get ET Statistics link to calculate the statistics.

Make it easier to digitize

Turn on the layer named "NAIP (2015 aerial imagery)" to see an image from which you can more easily digitize field boundaries. You must temporarily hide the ET dataset by clicking the Hide ET datset button.

Select Area by Polygon — From Irrigated Lands

This tool allows you to use one of the irrigated lands datasets, created by the IDWR, to assist you in selecting your area-of-interest. Each dataset contains all of the field-boundaries for the irrigated lands in the ESPA for that year. The features are categorized as 'irrigated, 'semi-irrigated' or 'non-irrigated.' A legend is provided so that you can tell the difference. The years for which these datasets were created closely match the years of the ET datasets. The last year of irrigated lands currently provided by this application is 2011. If you are calculating statistics on a newer ET dataset, find the irrigated-lands dataset from which you can select the area of your area-of-interest. When selecting polygons from the Irrigated Lands layers, coincident field boundaries will be removed from the output-PDF map. For example, if you select a circle representing land irrigated with a center-pivot sprinkler and then select the four corners surrounding it, the polygon in the output-PDF will be drawn as a rectangle. So, you can use any year of irrigated lands — and select polygons from any category (irrigated, semi- or non-irrigated) — in order to accurately define your area-of-interest.

Click on as many irrigated lands polygons as you need to define your area-of-interest. You may click on a previously selected polygon to remove it from the selection. When the From Irrigated Lands tool is activated, a toolbar is presented which allows you select an irrigated lands dataset for a different year, change the transparency of the dataset or temporarily hide the selected polygons so that the ET dataset is visible. It also shows the approximate number of acres selected as well as some help and a legend for the datasets.

Click the Get ET Statistics link to calculate the statistics. Note: you can continue to select/deselect polygons and re-calculate statistics, if you wish.

Get ET Statistics

The Get ET Statistics link operates on the selected method (whichever method is indicated by the radio button). When you click the link, the ET and CIR statistics will be calculated from the current ET dataset, using your area-of-interest as the subset.   Warning! This operation may take a few minutes to calculate the statistics if you chose a large area.

If you try to get the ET statistics but have not selected an area-of-interest using the chosen method you will receive an error message. For example, if you searched for a water right but the selected statistics-method was 'irrigation entities' or 'select area by polygon', you will see the following:


Calculate the Statistics

The statistics will be displayed at the lower right corner of the page, along with links to methods to see more details (min, max, range and standard deviation), create a PDF or save the statistics as a CSV-formatted file. This example shows four polygons, selected from the 2011 Irrigated Lands dataset (which has been set to be transparent so that the ET dataset is visible). CIR statistics will be calculated for seasonal ET datasets, but not for monthly datasets. In the case of seasonal ET datasets for western Idaho for the year 2000, there are no associated CIR datasets. So, you will see only ET statistics. If you wish to save the detailed statistics, you must select and copy them from the pop-up dialog:

Save the Statistics

You may save the statistics as CSV-formatted file or a PDF (which includes the map for the selected area). Here is an example of a PDF generated from the irrigated lands polygons example and another one showing that part of the selected area lies within an IDWR Regulatory Area:
Note that, in cases where the polygons used to define your area-of-interest are very large and complex, the output map (in the PDF) may not show the Public Land Survey lines or layers from the the IDWR regulatory areas.

Contact Us

Contact the IDWR Geospatial Technology Section if you experience problems using this site. Please include a detailed description of the problem you are having and the address of the web page you are using.