How to Calculate and Solve for Evapotranspiration | Jensen Haide Method | Methods of Application of Water

Last Updated on October 1, 2020

The image above represents evapotranspiration.

To compute for evapotranspiration, four essential parameters are needed and these parameters are Temperature co-efficient (c_t), Mean dialy temperature (T), Intercept on the Temperature (T_x) and Incident solar radiation (R_s).

The formula for calculating evapotranspiration:

E_tp = c_t(T – T_x)R_s

Where:

E_tp = Evapotranspiration
c_t = Temperature Co-efficient
T = Mean Daily Temperature
T_x = Intercept on the Temperature
R_s = Incident Solar Radiation

Let’s solve an example;
Find the evapotranspiration when the temperature co-efficient is 11, the mean dialy temperature is 21, the intercept on the temperature is 7 and the incident solar radiation is 4.

This implies that;

c_t = Temperature Co-efficient = 11
T = Mean Daily Temperature = 21
T_x = Intercept on the Temperature = 7
R_s = Incident Solar Radiation = 4

E_tp = c_t(T – T_x)R_s
E_tp = 11(21 – 7)(4)
E_tp = 11(14)(4)
E_tp = 616

Therefore, the evapotranspiration is 616.

Calculating the Temperature Co-efficient when the Evapotranspiration, the Mean Dialy Temperature, the Intercept on the Temperature and the Incident Solar Radiation is Given.

c_t = ^E_tp / _{(T – Tx) Rs}

Where;

c_t = Temperature Co-efficient
E_tp = Evapotranspiration
T = Mean Daily Temperature
T_x = Intercept on the Temperature
R_s = Incident Solar Radiation

Let’s solve an example;
Find the temperature co-efficient when the evapotranspiration is 44, the mean daily temperature is 20, the intercept on the temperature is 12 and the incident solar radiation is 4.

This implies that;

E_tp = Evapotranspiration = 44
T = Mean Daily Temperature = 20
T_x = Intercept on the Temperature = 12
R_s = Incident Solar Radiation = 4

c_t = ^E_tp / _{(T – Tx) Rs}
c_t = ⁴⁴ / _{(20 – 12) 4}
c_t = ⁴⁴ / _{(8) 4}
c_t = ⁴⁴ / ₃₂
c_t = 1.375

Therefore, the temperature co-efficient is 1.375.

Calculating the Mean Dialy Temperature when the Evapotranspiration, the Temeperature Co-efficient, the Intercept on the Temperature and the Incident Solar Radiation is Given.

T = ^E_tp / _{ct x Rs} + T_x

Where;

T = Mean Daily Temperature
E_tp = Evapotranspiration
c_t = Temperature Co-efficient
T_x = Intercept on the Temperature
R_s = Incident Solar Radiation

Let’s Solve an example;
Find the mean daily temperature when the Evapotranspiration is 35, the temperature co-efficient is 10, the intercept on the temperature is 8 and the incident solar radiation is 1.

This implies that;

E_tp = Evapotranspiration = 35
c_t = Temperature Co-efficient = 10
T_x = Intercept on the Temperature = 8
R_s = Incident Solar Radiation = 1

T = ^E_tp / _{ct x Rs} + T_x
T = ³⁵ / _{10 x 1} + 8
T = ³⁵ / ₁₀ + 8
T = 3.5 + 8
T = 11.5

Therefore, the mean dialy temperature is 11.5.

Calculating the Intercept on the Temperature when the Evapotranspiration, the Temperature Co-efficient, the Mean Dialy Temperature and the Incident Solar Radiation.

T_x = ^E_tp / _{ct x Rs} – T

Where;

T_x = Intercept on the Temperature
E_tp = Evapotranspiration
c_t = Temperature Co-efficient
T = Mean Daily Temperature
R_s = Incident Solar Radiation

Let’s solve an example;
Find the intercept on the temperature when the evapotranspiration is 52, the temperature co-efficient is 4, the mean daily temperature is 3 and the incident solar radiation is 2.

This implies that;

E_tp = Evapotranspiration = 52
c_t = Temperature Co-efficient = 4
T = Mean Daily Temperature = 3
R_s = Incident Solar Radiation = 2

T_x = ^E_tp / _{ct x Rs} – T
T_x = ⁵² / _{4 x 2} – 3
T_x = ⁵² / ₈ – 3
T_x = 6.5 – 3
T_x = 3.5

Therefore, the intercept on the temperature is 3.5.

Calculating the Incident Solar Radiation when the Evapotranspiration, the Temperature Co-efficient, the Mean Daily Temperature and the Intercept on the Temperature is Given.

R_s = ^E_tp / _{ct (T – Tx)}

Where;

R_s = Incident Solar Radiation
E_tp = Evapotranspiration
c_t = Temperature Co-efficient
T = Mean Daily Temperature
T_x = Intercept on the Temperature

Let’s solve an example;
Find the incident solar radiation when the evapotranspiration is 40, the temperature co-efficient is 14, the mean dialy temperature is 8 and the intercept on the temperature is 4.

This implies that;

E_tp = Evapotranspiration = 40
c_t = Temperature Co-efficient = 14
T = Mean Daily Temperature = 8
T_x = Intercept on the Temperature = 4

R_s = ^E_tp / _{ct (T – Tx)}
R_s = ⁴⁰ / _{14 (8 – 4)}
R_s = ⁴⁰ / _{14 (4)}
R_s = ⁴⁰ / ₅₆
R_s = 0.714

Therefore, the incident solar temperature is 0.714.

Nickzom Calculator – The Calculator Encyclopedia is capable of calculating the evapotranspiration.

To get the answer and workings of the evapotranspiration 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 Methods of Application of Water under Agricultural

Now, Click on Evapotranspiration | Jensen Haide 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 Temperature co-efficient (c_t), Mean dialy temperature (T), Intercept on the Temperature (T_x) and Incident solar radiation (R_s).

Now, enter the values appropriately and accordingly for the parameters as required by the Temperature co-efficient (c_t) is 11, Mean dialy temperature (T) is 21, Intercept on the Temperature (T_x) is 7 and Incident solar radiation (R_s) is 4.

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.