Evapotranspiration, what's this?

The evapotranspiration is the combination of two processes:
1. evaporation from the soil and the surface covered by the plants

2. transpiration from the leaves of the plants.

Thus, the calculation of ETo is used to know the amount of water necessary for the plants to have an optimal development.

Therefore, if you want to install an irrigation system, schedule irrigation cycles, or know the needs of each crop along the crop cycle, it is necessary to calculate this parameter as accurately as possible. It can be interpreted as the water demand exerted by the climate on the plant.


To estimate crop evapotranspiration (ETc) is obtained by function of two factor (ETc = Kc x ETo): reference crop evapotranspiration (ETo) and crop coefficient (Kc). ETo was introduced to study the evaporative demand of the atmosphere independently of crop type, crop stage development and management practices. ETo is only affected by climatic parameters, and is computed from weather data. Crop influences are accounted for by using a specific crop coefficient (Kc). However, Kc varies predominately with the specific crop characteristics.

What is the difference between ETP, ETo, ETc?

The word evapotranspiration is shortened to ETP. It can sometimes be found as ETo (Reference Evapotranspiration) or even ETp for Potential Evaporation.

In both cases, the climate demand is expressed to quantify the losses by soil evaporation and plant transpiration.

When we speak of ETc, we refer to the Evapotranspiration of a Crop. This means that a crop coefficient (Kc) has been applied to adapt this climatic demand to the characteristics of the crop.

Thus we have:

ETc = ETo x Kc

➡️ Kc used in the Sencrop App

➡️ More on the Irricrop


How do we calculate evapotranspiration?

We take 5 main factors into account:

  1. solar radiation

  2. relative humidity

  3. vapour pressure

  4. temperature

  5. wind speed

The analysis of the impact of the variation of temperature, insolation, wind speed and relative humidity reveals that the increase in wind which results in a decrease in relative humidity has a considerable effect on the reference evapotranspiration (Eto).

Evapotranspiration information is key to understanding and managing water resources systems.

The Food and Agricultural Organization of United Nations (FAO) improved and upgraded the methodologies described by FAO Penman- Monteith equation.

This approach was tested under different climates and time step calculations and is currently adopted worldwide. That’s the methodology we adopted.


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