This function calculates Penman-Monteith, Priestley Taylor and Hargreaves-Samani Potential Evapotranspiration using the method described by Allen et al, (1998)
calcEto(data, method = "PM", crop = "short", Zh = NULL)The function generates a list containing the following objects:
ET.Daily:
daily estimations of reference crop evapotranspiration (mm/day)
Ra.Daily:
daily estimations of extraterristrial radiation (MJ/m2/day)
Slope.Daily:
daily estimations of slope of vapour pressure curve (kPa/°C)
ET.type:
type of the estimation obtained
a dataframe containing the required climate variables: columns must contain the following parameters:
Lat: latitude of the site in decimal
degrees.
Lon: longitude of the site in decimal
degrees.
Elev: elevation above sea level in (
meters).
Year: year of record "YYYY".
Month: month of record "MM".
Day: day of record "DD".
Tmax: daily maximum temperature at 2-m
height in (°C).
Tmin: daily minimum temperature at 2-m
height in (°C).
Rs: daily surface incoming solar
radiation in (MJ/m^2/day).
RH or RHmax and RHmin: daily relative
humidity at 2-m height.
Tdew: daily dew point temperature at
2-m height in (°C).
U2 or Uz: daily wind speed at 2-m or
Z-m(custom) height (m/s).
the formulation used to compute Eto; default is
method = "PM" gives the the Penman-Monteith formulation;
method = "PT" gives the Priestley-Taylor formulation and
method = "HS" gives the Hargreaves-Samani formulation.
either crop = "short" (default) or
crop = "tall"; short indicates the method for FAO-56 hypothetical
short grass will be applied (Allen et al.1998); tall indicates that
the method for ASCE-EWRI standard crop will be applied (ASCE, 2005).
height of wind speed measurement in meters,
Penman-Monteith: If all variables of Tmax, Tmin, Rs, either U2 or Uz, and either RHmax and RHmin or RH or Tdew are available and crop surface (short or tall) is specified in argument the Penman-Monteith FAO56 formulation is used (Allen et al.1998).
Priestley-Taylor: If all variables of Tmax, Tmin, Rs and either RHmax and RHmin or RH or Tdew are available the Priestley-Taylor formulation is used (Priestley and Taylor, 1972).
Hargreaves-Samani: If only Tmax and Tmin are available, the Hargreaves-Samani formulation is used or estimating reference crop evapotranspiration (Hargreaves and. Samani, 1985).
Allen, R.G., L.S. Pereira, D. Raes, and M. Smith. 1998. ‘Crop evapotranspiration-Guidelines for Computing Crop Water requirements FAO Irrigation and Drainage Paper 56’. FAO, Rome 300: 6541.
Allen, R. G. 2005. The ASCE standardized reference evapotranspiration equation. Amer Society of Civil Engineers.
Guo, Danlu & Westra, Seth & Maier, Holger. (2016). An R package for modelling actual, potential and reference evapotranspiration. Environmental Modelling & Software. 78. 216-224. 10.1016/j.envsoft.2015.12.019.
Hargreaves, G.H.Samani, Z.A. 1985, Reference crop evapotranspiration from ambient air temperature. American Society of Agricultural Engineers.
Priestley, C. & Taylor, R. 1972, On the assessment of surface heat flux and evaporation using large-scale parameters'. Monthly Weather Review, vol. 100, no. 2, pp. 81-92.
climateData, calcWatBal, calcSeasCal
# load example data:
data(climateData)
calcEto(climateData, method = "HS")
# load example data:
data(AgroClimateData)
calcEto(AgroClimateData, method = "PM", crop = "short")
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