Landscape Irrigation Calculator for Utah

How to Use the Landscape Calculator

Please note that the reference evapotranspiration and precipitation data utilized in this calculator are sourced from the Utah Climate Center. The plant factor information has been compiled by referencing various factsheets published through Utah State University Extension.

Selecting the Location:

The locations listed here are named to correspond to the names of weather stations provided by the Global Historical Climatology Network (GHCN) and the Utah Climate Center. In the dropdown list for location, choose the city or place name that is nearest to your site. If you encounter difficulties finding the site name, please contact shital.poudyal@usu.edu for assistance. Alternatively, you can also visit the Utah Climate Center and get the name of station closest to your site and make the appropriate selection.

Selecting the Month:

Pick the month for which you want to calculate the irrigation requirement. Keep in mind that the output represents the total water requirement for the entire month. It's up to the user to decide at what interval to apply that volume of water. If you prefer to budget the total water required for the entire year, select "annual." The calculator will provide irrigation amount for any month in the year. However please follow your county or state guidelines on when to start and stop irrigation each season.

Selecting Vegetation/Plants:

When you explore the dropdown list, you'll find a wide range of options for plant selection. Choose the appropriate plant or vegetation type for your landscape. If your landscape consists of a mix of plants in each irrigation zone, select the plant with the highest water use. We've assigned plant factors to various plant types as follows:

• 0.8 = Cool-season turf,
• 0.5 = Warm-season turf,
• 0.6 = Low-water-use turf,
• 0.9 = Newly planted landscape or annual flowers,
• 0.4 = Low-water-use or native trees or native shrubs,
• 0.8 = Mature broadleaf non-native trees,
• 0.7 = Mature non-native shrubs,
• 0.85 = Vegetables and fruits

If you wish to use your own plant factor value, calculate the answer using the “cool season turf” and then multiply the answer by (desired plant factor value/0.8). That will be your landscape water need.

Selecting Area:

Enter the total irrigation area in square feet. If you're unsure of the area, you can estimate it using free online tools such as Google Earth, draft logic etc.

Selecting How Efficient Is Your Irrigation System:

Here, you need to input the efficiency of your irrigation system as a percentage (do not include the percentage sign). A system with 70% to 80% efficiency is considered efficient for overhead irrigation, while 90% to 95% is considered efficient for drip irrigation. Enter the appropriate percentage in the provided box.

Selecting Do You Want to Adjust Irrigation Based on Historic Monthly Precipitation Data:

The dropdown offers "Yes" and "No" options. If you select "Yes," the calculator will use historical average precipitation data and deduct it from the total water required. If you choose "No," the calculator will provide a figure based solely on water loss/evapotranspiration. Since precipitation is less consistent than evapotranspiration, you will need to carefully consider this option based on the purpose for using calculator. If you select "No" when determining monthly water needs and would like to adjust precipitation based on current data, you can select ‘No’ and then manually subtract the precipitation amount in gallons from the calculated value.

To convert precipitation from inches to gallons use : Precipitation (gallons) = Landscape Area (square feet) x rainfall (inches) x 0.623