et0_pm: Estimate ET0 by FAO-56 Penman-Monteithe quation.

In Sibada/sibadaR: Sibada's accumulated R scripts for next probably use to avoid reinventing the wheel.

Description

Estimate reference evapotranspiration (ET0) from a hypothetical short grass reference surface using the FAO-56 Penman-Monteithe quation (equation 6 in Allen et al. (1998))

Usage

et0_pm(Rs, tmax, tmin, ws, Rso, G = 0, h.ws = 10, albedo = 0.23,
  delta = NULL, gamma = NULL, z = NULL, ea = NULL, es = NULL,
  rhmean = NULL, pres = NULL)

Arguments

Rs	Incoming shortwave radiation at crop surface [MJ m-2 day-1].
tmax	Daily maximum air temperature at 2m height [deg Celsius].
tmin	Daily minimum air temperature at 2m height [deg Celsius].
ws	Wind speed [m s-1].
Rso	Clear sky incoming shortwave radiation, i. e. extraterrestrial radiation multiply by clear sky transmissivity (i. e. a + b, a and b are coefficients of Angstrom formula. Normally 0.75) [MJ m-2 day-1].
G	Soil heat flux [MJ m-2 day-1]. Normally set to 0.0 when the time steps are less than 10 days. Should be calculated in monthly or longer time step. Default 0.0.
h.ws	Height where measure the wind speed [m]. Default 10m.
albedo	Albedo of the crop as the proportion of gross incoming solar radiation that is reflected by the surface. Default 0.23 (i. e. the value of the short grass reference crop defined by the FAO).
delta	Slope of the saturation vapour pressure curve. Can be estimated by air temperature if is not provided.
gamma	Psychrometric constant [kPa Celsius -1]. Can be estimated by the air pressure or elevation if is not provided.
z	Elevation above sea level [m]. Must provided if gamma and pres are not provided.
ea	Actual vapor pressure [kPa]. Can be estimated by maximum or minimum air temperature and mean relative humidity.
es	Saturated vapor pressure [kPa]. Can be estimated by maximum or minimum air temperature if is not provided.
rhmean	Daily mean relative humidity [ the actual vapor pressure would be estimated by minimum air temperature.
pres	Air pressure [kPa]. If not provided, must provide z.

Value

Reference evapotranspiration ET0 from a hypothetical grass reference surface [mm day-1].

Sibada/sibadaR documentation built on Jan. 31, 2020, 6:40 p.m.