Commercial irrigation

What is ETo?

If you are considering installing a garden irrigation system for your property, you should be aware of how much water your lawn or garden will require based on the needs of the types of plants in the landscape. The number of sprinkler heads will affect your water usage as well; more outlets for water mean more water being used by the system as a whole. To accurately estimate your total water usage, the rate of use, and the cost of use, you’ll want to know a few measures and make a few calculations.


Evapotranspiration (ET) is the measure of the amount of evaporation and plant transpiration from the surface of the landscape to the atmosphere. Evaporation refers to the water lost to the air from the soil, rocks, and other surfaces in the landscape. Transpiration refers to the water that plants move through their bodies and lose through their leaves. Both of these processes taken together are known as evapotranspiration.


The rate of evapotranspiration from a short, green grass surface (the reference) is called the reference crop evapotranspiration or reference evapotranspiration, or ETo.

According to the University of Idaho, “ETo was introduced to study the evaporative demand of the atmosphere independently of crop type, crop development and management practices. As water is abundantly available at the reference evapotranspiring surface, soil factors do not affect ET. The only factors affecting ETo are climatic parameters. Consequently, ETo is a climatic parameter and can be computed from weather data. ETo expresses the evaporating power of the atmosphere at a specific location and time of the year.”

Horticulturists and urban landscape planners use ETo to accurately estimate the water requirements of plants they may use and make decisions based on that data.


Potential evapotranspiration (PET) is the amount of water that would be evaporated and transpired if there were sufficient water available in the soil. This demand incorporates the energy available for evaporation and the ability of the lower atmosphere to transport evaporated moisture away from the land surface. Potential evapotranspiration is higher in the summer, on less cloudy days, and closer to the equator, because of the higher levels of solar radiation that provides the energy for evaporation. Potential evapotranspiration is also higher on windy days because the evaporated moisture can be quickly moved from the ground or plant surface, allowing more evaporation to fill its place.

The team at Fairfiled Irrigation are experts in designing, installing, and maintaining lawn sprinkler systemsand commercial irrigations throughout Fairfield County. The suburban/rural nature of the area means that Fairfield Irrigation has the experience that best fits your project or needs. Trust them to advise you about what your landscape irrigation needs are and need to be for a healthy and productive landscape or garden.

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