Potential evapotranspiration or PE is a measure of the ability of the atmosphere to remove water from the surface through the processes of evaporation and transpiration assuming no control on water supply. Actual evapotranspiration or AE is the quantity of water that is actually removed from a surface due to the processes of evaporation and transpiration.

Potential evapotranspiration (PE) is the maximum attainable or achievable Evapotranspiration for a given crop due to evaporation and transpiration. On the other hand, Actual evapotranspiration (AE) is the quantity of water that is actually removed from a due to the processes of evaporation and transpiration. Determining both these quantities is crucial for calculating the actual crop water need that is PE - AE.

Hope this answer helps

Dear Dr. Samuel Akande

You can check with Handbook of Hydrology by David R Maidment for more detailed understanding.

Regards

Miyuru

Potential evapotranspiration is the amount of evapotranspiration that is expected over a surface with no limitaion of water.

Actual Evapotranspiration is amount of evapotranspiration that actually occurs when water is limited.

For lake :-

Potential evapotranspiration=Actual Evapotranspiration

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/potential-evapotranspiration

Hello Samuel,

PET can be identified as the ability of the environment to take up the water from the land and transfer it to gas; also, PET is the maximum amount of water that is going to evaporate when there is available water, such as in a lake. PET is a function of relative humidity, solar radiation, water availability, wind, and temperature. AET or ET is how much water is going to evaporate when there is a water limitation. AET is a function of vegetation cover, root, and soil. Usually, PET is larger than ET.

I hope this is helpful.

Potential evapotranspiration is the loss of water from the crop and its surrounding soil which is taken into account when the sufficient moisture is freely available to completely meet the needs of the crop fully covering an area while actual evapotranspiration is an actual loss of water from the crop and surrounding soil from the prevailing condition.

Hope this answer helps

https://www.researchgate.net/publication/325274523_Estimation_of_Evapotranspiration_using_CROPWAT_80_Model_for_Shipra_River_Basin_in_Madhya_Pradesh

Is it possible that PET>ET?

When plant face no water stress, the ET is maximum and called PET. This happend in potential conditions and it is rare.

Otherwise, the ET is lower than maximum (PET) and called AET.

Please note that the concept of potential evapotranspiration (PET) is no longer used in irrigation, and it has been replaced by reference crop evapotranspiration (ETo) because of certain reasons. I will explain these two concepts first, and then come to actual evapotranspiration.

The potential evapotranspiration concept was first introduced in the late 1940s. It was defined as “the amount of evapotranspiration in a given time by a large vegetation of short green crop, completely shading the ground, of uniform height and with adequate moisture at all the times in the soil”. The major objective in bringing this “potential” evapotranspiration concept was to remove the effects specific to crops in the evapotranspiration process.

The notion of PET was well accepted by the scientific fraternity, and it became the focal idea in estimating crop water use for a long time. After some time, however, certain limitations cropped up. In the definition of PET, the ET rate was not related to a specific crop. The main confusion with PET was that there were many types of crops that fitted into the description of a ‘short green crop’, and one might be confused as to which short crop should be selected! Having considered the ambiguities and limitations of PET, by the early 1980s, the concept of “reference crop evapotranspiration” (ETo) was introduced.

The major objective of introducing ETo was to assess the evapotranspiration demand of the atmosphere independently without considering the effects of crops, cultivar differences, crop development, and management practices.

In reference evapotranspiration, the reference surface closely resembles an extensive surface of green grass of uniform height, actively growing, completely shading the ground, and with adequate water. The FAO Expert Consultation on Revision of FAO Methodologies for Crop Water Requirements (1990) after specifying the reference surface explicitly, defines reference evapotranspiration as : “the rate of evapotranspiration from a hypothetical reference crop with an assumed crop height of 0.12m, a fixed surface resistance of 70 s/m and an albedo of 0.23, closely resembling the evapotranspiration from an extensive surface of green grass of uniform height, actively growing, well-watered, and completely shading the ground.”

"Actual crop evapotranspiration" (ETa) or simply "crop evapotranspiration" (ETc) refers to the evapotranspiration by a particular crop in a given period under the prevailing soil, water, and atmospheric conditions. Actual crop evapotranspiration can be defined “as the evapotranspiration from disease-free, well-fertilized crops grown in large fields under optimum soil water conditions, which achieve full production under the given climatic conditions”.

ETa can be determined by direct methods such as lysimeters or estimated from climatic data by integrating the effect of crop characteristics into ETo. The ratio of crop ET to reference ET (ETa/ETo), called crop coefficient (Kc), is used to relate them as given in the following relationship..

ETa = ETo x Kc

Where, ETa = Actual crop evapotranspiration (mm/day); ETo = Reference crop evapotranspiration (mm/day); and Kc = Crop coefficient

I invite all of to have a review of my latest book “Irrigation and Water Management”, where issues of this kind are discussed in a contemporary style. Please visit

https://www.researchgate.net/publication/354616406_Irrigation_and_Water_Managementor or

www.anebooks.com