Penman Equation - Shuttleworth (1993)

Shuttleworth (1993)

In 1993, W.Jim Shuttleworth modified and adapted the Penman equation to use SI, which made calculating evaporation simpler. The resultant equation is:

$E_{mass}=\frac{m R_n + \gamma * 6.43\left(1+0.536 * U_2 \right)\delta e}{\lambda_v \left(m + \gamma \right) }$

where:

E_mass = Evaporation rate (m day-1)

m = Slope of the saturation vapor pressure curve (kPa K-1)

R_n = Net irradiance (MJ m-2 day-1)

γ = psychrometric constant = (kPa K-1)

U₂ = wind speed (m s-1)

δe = vapor pressure deficit (kPa)

λ_v = latent heat of vaporization (MJ kg-1)

Note: this formula implicitly includes the division of the numerator by the density of water (1000 kg m-3) to obtain evaporation in units of m d-1

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