Evapotranspiration (ET)

With the knowledge of the specific crop you will grow, you need to determine its water requirement.

A plant’s water requirement is measured by evapotranspiration, which is primarily determined by climate factors (solar radiation, temperature, humidity, and wind).

Evapotranspiration (ET) = the total quantity of water that is:

Used by the crops for transpiration, including evaporation from the plant itself

Lost through evaporation from the soil surface


Rule of thumb for the late stages of crops – ET is generally 10% evaporation and 90% transpiration.


The rate of evapotranspiration is not static. It fluctuates daily, with trends across seasons.

  • Solar radiation, temperature and wind speed increase ET
  • Humidity decreases ET.


In general, we work with a standardized measurement being the reference evapotranspiration rate (ETo). FYI, the standardization is based upon a reference crop of vegetative grass.

Explore the next module, or search for a specific topic or issue.

Before using these modules, please familiarize yourself with the relevant disclaimers and additional safety and usage information contained within each module.

© 2023, Rivulis Irrigation Ltd, all rights reserved. 
Reproduction of this content in any form is prohibited without the written consent of Rivulis Irrigation Ltd.