Penman's Equation Calculator

✖Slope of Saturation Vapour Pressure vs temperature curve at the mean air temperature, in mm of mercury per °C.ⓘ Slope of Saturation Vapour Pressure [A]			+10% -10%
✖Net Radiation of Evaporable Water length per day influenced by the incoming solar radiation absorbed by the Earth's surface and the radiation reflected back.ⓘ Net Radiation of Evaporable Water [H_n]			+10% -10%
✖Parameter of Wind Velocity and Saturation Deficit.ⓘ Parameter of Wind Velocity and Saturation Deficit [E_a]			+10% -10%
✖Psychrometric Constant relates the partial pressure of water in air to the air temperature.ⓘ Psychrometric Constant [γ]			+10% -10%

✖Daily Potential Evapotranspiration is the process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants.ⓘ Penman's Equation [PET]

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Formula

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Penman's Equation

Formula

`"PET" = ("A"*"H"_{"n"}+"E"_{"a"}*"γ")/("A"+"γ")`

Example

`"2.059364"=("1.05"*"1.99"+"2.208"*"0.49")/("1.05"+"0.49")`

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Penman's Equation Solution

STEP 0: Pre-Calculation Summary

Formula Used

Daily Potential Evapotranspiration = (Slope of Saturation Vapour Pressure*Net Radiation of Evaporable Water+Parameter of Wind Velocity and Saturation Deficit*Psychrometric Constant)/(Slope of Saturation Vapour Pressure+Psychrometric Constant)
PET = (A*H_n+E_a*γ)/(A+γ)
This formula uses 5 Variables

Variables Used

Daily Potential Evapotranspiration - Daily Potential Evapotranspiration is the process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants.
Slope of Saturation Vapour Pressure - Slope of Saturation Vapour Pressure vs temperature curve at the mean air temperature, in mm of mercury per °C.
Net Radiation of Evaporable Water - Net Radiation of Evaporable Water length per day influenced by the incoming solar radiation absorbed by the Earth's surface and the radiation reflected back.
Parameter of Wind Velocity and Saturation Deficit - Parameter of Wind Velocity and Saturation Deficit.
Psychrometric Constant - Psychrometric Constant relates the partial pressure of water in air to the air temperature.

STEP 1: Convert Input(s) to Base Unit

Slope of Saturation Vapour Pressure: 1.05 --> No Conversion Required
Net Radiation of Evaporable Water: 1.99 --> No Conversion Required
Parameter of Wind Velocity and Saturation Deficit: 2.208 --> No Conversion Required
Psychrometric Constant: 0.49 --> No Conversion Required

STEP 2: Evaluate Formula

Substituting Input Values in Formula

PET = (A*H_n+E_a*γ)/(A+γ) --> (1.05*1.99+2.208*0.49)/(1.05+0.49)

Evaluating ... ...

PET = 2.05936363636364

STEP 3: Convert Result to Output's Unit

2.05936363636364 --> No Conversion Required

FINAL ANSWER

2.05936363636364 ≈ 2.059364 <-- Daily Potential Evapotranspiration

(Calculation completed in 00.004 seconds)

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< 8 Evapotranspiration Equations Calculators

Equation for Net Radiation of Evaporable Water

Go Net Radiation of Evaporable Water = Incident Solar Radiation Outside the Atmosphere*(1-Reflection Coefficient)*(Constant depending on Latitude+(A constant*Actual Duration of Bright Sunshine/Maximum Possible Hours of Bright Sunshine))-Stefan-Boltzmann constant*Mean Air Temperature^4*(0.56-0.092*sqrt(Actual Vapour Pressure))*(0.1+(0.9*Actual Duration of Bright Sunshine/Maximum Possible Hours of Bright Sunshine))

Net Radiation of Evaporable water given Daily Potential Evapotranspiration

Go Net Radiation of Evaporable Water = (Daily Potential Evapotranspiration*(Slope of Saturation Vapour Pressure+Psychrometric Constant)-(Parameter of Wind Velocity and Saturation Deficit*Psychrometric Constant))/Slope of Saturation Vapour Pressure

Parameter Including Wind Velocity and Saturation Deficit

Go Parameter of Wind Velocity and Saturation Deficit = (Daily Potential Evapotranspiration*(Slope of Saturation Vapour Pressure+Psychrometric Constant)-(Slope of Saturation Vapour Pressure*Net Radiation of Evaporable Water))/Psychrometric Constant

Penman's Equation

Go Daily Potential Evapotranspiration = (Slope of Saturation Vapour Pressure*Net Radiation of Evaporable Water+Parameter of Wind Velocity and Saturation Deficit*Psychrometric Constant)/(Slope of Saturation Vapour Pressure+Psychrometric Constant)

Mean Monthly Air Temperature for Potential Evapotranspiration in Thornthwaite Equation

Go Mean Air Temperature = (Potential Evapotranspiration in Crop Season/(1.6*Adjustment Factor))^(1/An Empirical Constant)*(Total Heat Index/10)

Adjustment related to Latitude of Place given Potential Evapotranspiration

Go Adjustment Factor = Potential Evapotranspiration in Crop Season/(1.6*((10*Mean Air Temperature)/Total Heat Index)^An Empirical Constant)

Thornthwaite Formula

Go Potential Evapotranspiration in Crop Season = 1.6*Adjustment Factor*((10*Mean Air Temperature)/Total Heat Index)^An Empirical Constant

Equation for Blaney Criddle

Go Potential Evapotranspiration in Crop Season = 2.54*An Empirical Coefficient*Sum of Monthly Consumptive Use factors

Penman's Equation Formula

What is Penman Formula?

The Penman Formula is a semi-empirical equation combining mass transfer (Ea) and energy budget (H) methods. Penman's equation requires daily mean temperature, wind speed, air pressure, and solar radiation to predict Evaporation E.

How to Calculate Penman's Equation?

Penman's Equation calculator uses Daily Potential Evapotranspiration = (Slope of Saturation Vapour Pressure*Net Radiation of Evaporable Water+Parameter of Wind Velocity and Saturation Deficit*Psychrometric Constant)/(Slope of Saturation Vapour Pressure+Psychrometric Constant) to calculate the Daily Potential Evapotranspiration, The Penman's Equation formula is defined as the evaporation (E) from an open water surface and was developed by Howard Penman in 1948. Daily Potential Evapotranspiration is denoted by PET symbol.

How to calculate Penman's Equation using this online calculator? To use this online calculator for Penman's Equation, enter Slope of Saturation Vapour Pressure (A), Net Radiation of Evaporable Water (H_n), Parameter of Wind Velocity and Saturation Deficit (E_a) & Psychrometric Constant (γ) and hit the calculate button. Here is how the Penman's Equation calculation can be explained with given input values -> 2.059364 = (1.05*1.99+2.208*0.49)/(1.05+0.49).

FAQ

What is Penman's Equation?

The Penman's Equation formula is defined as the evaporation (E) from an open water surface and was developed by Howard Penman in 1948 and is represented as PET = (A*H_n+E_a*γ)/(A+γ) or Daily Potential Evapotranspiration = (Slope of Saturation Vapour Pressure*Net Radiation of Evaporable Water+Parameter of Wind Velocity and Saturation Deficit*Psychrometric Constant)/(Slope of Saturation Vapour Pressure+Psychrometric Constant). Slope of Saturation Vapour Pressure vs temperature curve at the mean air temperature, in mm of mercury per °C, Net Radiation of Evaporable Water length per day influenced by the incoming solar radiation absorbed by the Earth's surface and the radiation reflected back, Parameter of Wind Velocity and Saturation Deficit & Psychrometric Constant relates the partial pressure of water in air to the air temperature.

How to calculate Penman's Equation?

The Penman's Equation formula is defined as the evaporation (E) from an open water surface and was developed by Howard Penman in 1948 is calculated using Daily Potential Evapotranspiration = (Slope of Saturation Vapour Pressure*Net Radiation of Evaporable Water+Parameter of Wind Velocity and Saturation Deficit*Psychrometric Constant)/(Slope of Saturation Vapour Pressure+Psychrometric Constant). To calculate Penman's Equation, you need Slope of Saturation Vapour Pressure (A), Net Radiation of Evaporable Water (H_n), Parameter of Wind Velocity and Saturation Deficit (E_a) & Psychrometric Constant (γ). With our tool, you need to enter the respective value for Slope of Saturation Vapour Pressure, Net Radiation of Evaporable Water, Parameter of Wind Velocity and Saturation Deficit & Psychrometric Constant and hit the calculate button. You can also select the units (if any) for Input(s) and the Output as well.

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