How to Calculate and Solve for Evaporation from Open Water Surface | Irrigation Water Requirement

The image above represents evaporation from the open water surface. To calculate evaporation from the open water surface, four essential parameters are needed, and these parameters are the Slope of Saturation Vapour Pressure vs. Temperature Curve (Δ), Net Radiation (Qn), Aerodynamic Component (Ea), and Psychometric Constant (Y).

The formula for calculating evaporation from open water surface:

E_o = ^{ΔQ_n + YE_a} / _{Δ + Y}

Where:

E_o = Evapouration from Open Water Surface
Δ = Slope of Saturation Vapour Pressure vs Temperature Curve
Q_n = Net Radiation
E_a = Aerodynamic Component
Y = Psychometric Constant

Let’s solve an example;
Find the evaporation from open water surface when the slope of saturation vapour pressure vs temperature curve is 20, the net radiation is 16, the aerodynamic component is 12 and psychometric constant is 10.

This implies that;

Δ = Slope of Saturation Vapour Pressure vs Temperature Curve = 20
Q_n = Net Radiation = 16
E_a = Aerodynamic Component = 12
Y = Psychometric Constant = 10

E_o = ^{ΔQ_n + YE_a} / _{Δ + Y}
E_o = ^{(20)(16) + (10)(12)} / _{20 + 10}
That is, E_o = ^{320 + 120} / ₃₀
E_o = ⁴⁴⁰ / ₃₀
E_o = 14.6

Therefore, the evaporation from open water surface is 14.6.

Read more: How to Calculate and Solve for Storage Difference | Irrigation Water Requirement

How to Calculate Evaporation from Open Water Surface Using Nickzom Calculator

Nickzom Calculator – The Calculator Encyclopedia is capable of calculating the evaporation from open water surface.

To get the answer and workings of the evaporation from open water surface using 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

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 Irrigation Water Requirement under Agricultural

Now, Click on Evaporation from Open Water Surface under Irrigation Water Requirement

The screenshot below displays the page or activity to enter your values, to get the answer for the evaporation from open water surface according to the respective parameters which is the Slope of Saturation Vapour Pressure vs Temperature Curve (Δ), Net Radiation (Q_n), Aerodynamic Component (E_a) and Psychometric Constant (Y).

Now, enter the values appropriately and accordingly for the parameters as required by the Slope of Saturation Vapour Pressure vs Temperature Curve (Δ) is 20, Net Radiation (Q_n) is 16, Aerodynamic Component (E_a) is 12 and Psychometric Constant (Y) is 10.

Finally, Click on Calculate

As you can see from the screenshot above, Nickzom Calculator– The Calculator Encyclopedia solves for the evaporation from the open water surfaces and presents the formula, workings, and steps too.