FAO-56 Penman-Monteith reference evapotranspiration (Eq. 6)

ET0 = (0.408 Delta (Rn - G) + gamma 900/(T+273) u2 VPD) / (Delta + gamma (1 + 0.34 u2)), Delta per Eq. 13, gamma = 0.665e-3 P per Eq. 8, G = 0 daily per Eq. 42. Reproduces the printed Example 18 (Uccle): ET0 = 3.88 mm/day from T 16.9, Rn 13.28, u2 2.078, VPD 0.589, P 100.1.

Usage

Basevap(T, R_n, u2, VPD, G = 0, P = 101.3)

Arguments

T

Mean daily air temperature at 2 m (deg C).

R_n

Net radiation (MJ m-2 day-1).

u2

Wind speed at 2 m (m/s).

VPD

Vapour pressure deficit es - ea (kPa).

G

Soil heat flux (MJ m-2 day-1), 0 daily.

P

Atmospheric pressure (kPa), 101.3 default.

Value

List with estimate, radiative_term, aerodynamic_term, delta, gamma, inputs, method.

References

Allen, R. G., Pereira, L. S., Raes, D. and Smith, M. (1998), FAO Irrigation and Drainage Paper 56, Eqs. 6, 8, 13, 42, Example 18; Zotarelli et al. (2010), Step by step calculation of the Penman-Monteith evapotranspiration (FAO-56 method), AE459.

Examples

Basevap(T = c(1, 2, 3, 4, 5, 6, 7, 8), R_n = c(1, 2, 3, 4, 5, 6, 7, 8),
  u2 = c(1, 2, 3, 4, 5, 6, 7, 8), VPD = c(1, 2, 3, 4, 5, 6, 7, 8))
#> $estimate
#> [1] 1.747833
#> 
#> $radiative_term
#> [1] 0.1404594
#> 
#> $aerodynamic_term
#> [1] 1.607373
#> 
#> $delta
#> [1] 0.04739112
#> 
#> $gamma
#> [1] 0.0673645
#> 
#> $T
#> [1] 1
#> 
#> $R_n
#> [1] 1
#> 
#> $u2
#> [1] 1
#> 
#> $VPD
#> [1] 1
#> 
#> $G
#> [1] 0
#> 
#> $P
#> [1] 101.3
#> 
#> $method
#> [1] "FAO-56 Penman-Monteith ET0 (Allen et al. 1998, Eq. 6)"
#>