The image above represents evapotranspiration. To calculate evapotranspiration, five essential parameters are needed and these parameters are Weighing Factor (W), Net Radiation (Rn), Function Value of Wind Velocity (f(u)), Saturated Vapour Pressure at Mean Density Pressure (ρs) and Actual Vapour Pressure of the Air (ρa).
The formula for calculating evapotranspiration:
Etp = WRn + (1 – W)f(u)(ρs – ρa)
Where:
Etp = Evapotranspiration
W = Weighing Factor
Rn = Net Radiation
f(u) = Function Value of Wind Velocity
ρs = Saturated Vapour Pressure at Mean Density Pressure
ρa = Actual Vapour Pressure of the Air
Let’s solve an example;
Find the evapotranspiration when the weighing factor is 7, the net radiation is 13, the function value of wind velocity is 11, saturated vapour pressure at mean density pressure is 8 and the actual vapour pressure of the air is 21.
This implies that;
W = Weighing Factor = 7
Rn = Net Radiation = 13
f(u) = Function Value of Wind Velocity = 11
ρs = Saturated Vapour Pressure at Mean Density Pressure = 8
ρa = Actual Vapour Pressure of the Air = 21
Etp = WRn + (1 – W)f(u)(ρs – ρa)
Etp = 7(13) + (1 – 7)(11)(8 – 21)
That is, Etp = 91 + (-6)(11)(-13)
Etp = 91 + 858
Etp = 949
Therefore, the evapotranspiration is 949.
How to Calculate Evapotranspiration | Modified Penman Method Using Nickzom Calculator
Nickzom Calculator – The Calculator Encyclopedia is capable of calculating evapotranspiration.
To get the answer and workings of evapotranspiration, use the Nickzom Calculator – The Calculator Encyclopedia. First, you need to obtain the app.
You can get this app via any of these means:
Web – https://www.nickzom.org/calculator-plus
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To get access to the professional version via web, you need to register and subscribe for NGN 2,000 per annum to have utter access to all functionalities.
You can also try the demo version via https://www.nickzom.org/calculator
Android (Paid) – https://play.google.com/store/apps/details?id=org.nickzom.nickzomcalculator
Android (Free) – https://play.google.com/store/apps/details?id=com.nickzom.nickzomcalculator
Apple (Paid) – https://itunes.apple.com/us/app/nickzom-calculator/id1331162702?mt=8
Once, you have obtained the calculator encyclopedia app, proceed to the Calculator Map, then click on Agricultural under Engineering.
Now, Click on Methods of Application of Water under Agricultural
Now, Click on Evapotranspiration | Modified Penman Method under Methods of Application of Water
The screenshot below displays the page or activity to enter your values, to get the answer for the evapotranspiration according to the respective parameters which is the Weighing Factor (W), Net Radiation (Rn), Function Value of Wind Velocity (f(u)), Saturated Vapour Pressure at Mean Density Pressure (ρs) and Actual Vapour Pressure of the Air (ρa).
Now, enter the values appropriately and accordingly for the parameters as required by the Weighing Factor (W) is 7, Net Radiation (Rn) is 13, Function Value of Wind Velocity (f(u)) is 11, Saturated Vapour Pressure at Mean Density Pressure (ρs) is 8 and Actual Vapour Pressure of the Air (ρa) is 21.
Finally, Click on Calculate
As you can see from the screenshot above, Nickzom Calculator– The Calculator Encyclopedia solves for the evapotranspiration and presents the formula, workings and steps too.
