What is ET?

Simply defined, evapotranspiration, or ET, is the rate of water loss from the landscape. It is nature's process of transferring moisture to the atmosphere by the evaporation of water from the soil and transpiration of water from plant surfaces. ET is used worldwide for determining crop irrigation needs and it provides a proven method for managing irrigation in any setting.

ET is typically measured in inches of water loss per unit of time. A common reference is inches per day. The rate of ET is influenced by four climactic variables:

• Air Temperature
• Relative Humidity
• Wind Speed
• Solar Radiation

ET is applied to irrigation by first measuring the reference rate of ET for a location and then adjusting for the specific crop or plant type at the site. The reference ET, or ETo, for a location is typically measured using ground level weather sensors and is based on a reference crop such as Kentucky bluegrass. Since researchers have determined coefficients, or adjustment factors, for virtually every plant type, these factors can be used to adjust the ET for any site to match the specific plant needs at that site.

To compute the irrigation requirements for the plants at your site, ETwater combines daily ET data gathered from a weather station near you and the information that you enter into the ETwater Manager website about your plants. Using this input, we compute an accurate watering schedule for each station at your landscape and adjust each station's schedule as needed on a daily basis.