METEOROLOGY – HUMIDITY & WATER VAPOUR CALCULATOR
Evaporation Penman
A precise tool.
What is the Evaporation Penman & How does it work?
The Penman equation is a widely used method for estimating open-water evaporation from a large water body. It accounts for both the energy available for evaporation and the resistance to evaporation due to air movement over the water surface.This equation is particularly useful in agricultural and hydrological applications where accurate estimation of evaporation rates is crucial.
E = frac{Delta (R_n – G) + gamma left(frac{900}{T+273} u_2 L_eright)}{Delta + gamma left(1 + 0.34 u_2^2right)}
E = Evaporation rate (mm/day)
Delta = Slope of the saturation vapor pressure curve (kPa/Β°C)
R_n = Net radiation at the surface (MJ/mΒ²/day)
G = Soil heat flux density (MJ/mΒ²/day)
gamma = Psychrometric constant (kPa/Β°C)
T = Air temperature (Β°C)
u_2 = Wind speed at 2 meters above the surface (m/s)
L_e = Latent heat of vaporization of water (MJ/kg)
Delta = Slope of the saturation vapor pressure curve (kPa/Β°C)
R_n = Net radiation at the surface (MJ/mΒ²/day)
G = Soil heat flux density (MJ/mΒ²/day)
gamma = Psychrometric constant (kPa/Β°C)
T = Air temperature (Β°C)
u_2 = Wind speed at 2 meters above the surface (m/s)
L_e = Latent heat of vaporization of water (MJ/kg)
Parameters
Result
β
Frequently Asked Questions
What is the Penman equation used for?
The Penman equation is used to estimate the rate of evaporation from a large water body by accounting for energy availability and air movement resistance.
What do the variables R_n, G, and u_2 represent in the Penman equation?
R_n represents net radiation at the surface (MJ/mΒ²/day), G is ground heat flux density (MJ/mΒ²/day), and u_2 is wind speed at 2 meters above the water surface (m/s).
How does the Penman equation account for air movement over water?
The equation includes a term that accounts for the resistance to evaporation due to air movement, which is influenced by wind speed.
What is the significance of the slope of the saturation vapor pressure curve (Ξ) in the Penman equation?
The slope Ξ represents how much the saturation vapor pressure changes with temperature and is crucial for calculating the energy available for evaporation.
Can this calculator be used for any type of water body?
This calculator is specifically designed for open-water bodies where the surface area is large enough to assume uniform conditions over the entire area.
Results are for informational purposes only and do not constitute professional advice.