Reference crop evapotranspiration in mm/day from Allen et al. (1998), eq. (6): $$ET_0 = \frac{0.408\Delta(R_n - G) + \gamma \frac{900}{T+273} u_2 D}{\Delta + \gamma(1 + 0.34 u_2)}$$ with \(\Delta\) from their eq. (13) and \(\gamma\) from their eq. (8). The two terms are returned separately: the first is the radiative (energy) contribution, the second the aerodynamic (vapour-transport) contribution.
Arguments
- T
Mean air temperature at 2 m, degrees Celsius.
- R_n
Net radiation at the crop surface, MJ m-2 day-1.
- u2
Wind speed at 2 m, m/s, non-negative.
- VPD
Vapour pressure deficit \(e_s - e_a\), kPa, non-negative.
- G
Soil heat flux density, MJ m-2 day-1, default 0 (the recommended daily value).
- P
Atmospheric pressure, kPa, default 101.3 (sea level).
Value
A list with estimate (ET0, mm/day),
radiative_term, aerodynamic_term, delta,
gamma, and the inputs T, R_n, u2,
VPD, G, P, plus method.
References
Allen, R. G., Pereira, L. S., Raes, D. and Smith, M. (1998). Crop evapotranspiration. FAO Irrigation and Drainage Paper 56.
Examples
morie_basEvap(T = 25, R_n = 15, u2 = 2, VPD = 1.5)
#> $estimate
#> [1] 5.847467
#>
#> $radiative_term
#> [1] 3.825466
#>
#> $aerodynamic_term
#> [1] 2.022001
#>
#> $delta
#> [1] 0.1886818
#>
#> $gamma
#> [1] 0.0673645
#>
#> $T
#> [1] 25
#>
#> $R_n
#> [1] 15
#>
#> $u2
#> [1] 2
#>
#> $VPD
#> [1] 1.5
#>
#> $G
#> [1] 0
#>
#> $P
#> [1] 101.3
#>
#> $method
#> [1] "FAO-56 Penman-Monteith ET0 (Allen et al. 1998, Eq. 6)"
#>