penman: Potential evapotranspiration

Description

Functions to calculate potential evapotranspiration using Penman or Penman-Monteith.

Usage

penman(
  latrad,
  elevation,
  slorad,
  asprad,
  J,
  Tmin,
  Tmax,
  RHmin,
  RHmax,
  R_s,
  u,
  z = 10,
  z0 = 0.001,
  alpha = 0.25,
  windfun = "1956"
)
penmanmonteith(rc, elevation, Tmin, Tmax, RHmin, RHmax, Rn, u = NA_real_)

Value

Potential evapotranspiration (in mm of water).

Arguments

latrad: Latitude in radians.
elevation: Elevation (in m).
slorad: Slope (in radians).
asprad: Aspect (in radians from North).
J: Julian day, number of days since January 1, 4713 BCE at noon UTC.
Tmin: Minimum temperature (degrees Celsius).
Tmax: Maximum temperature (degrees Celsius).
RHmin: Minimum relative humidity (percent).
RHmax: Maximum relative humidity (percent).
R_s: Solar radiation (MJ/m2).
u: With wind speed (m/s).
z: Wind measuring height (m).
z0: Roughness height (m).
alpha: Albedo.
windfun: Wind speed function version, either "1948" or "1956".
rc: Canopy vapour flux (stomatal) resistance (s·m-1).
Rn: Daily net radiation (MJ·m-2·day-1).

Functions

penmanmonteith(): Penman Monteith method

Author

Miquel De Cáceres Ainsa, CREAF

Details

The code was adapted from package `Evapotranspiration', which follows McMahon et al. (2013). If wind speed is not available, an alternative formulation for potential evapotranspiration is used as an approximation (Valiantzas 2006)

References

Penman, H. L. 1948. Natural evaporation from open water, bare soil and grass. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 193, 120-145.

Penman, H. L. 1956. Evaporation: An introductory survey. Netherlands Journal of Agricultural Science, 4, 9-29.

McMahon, T.A., Peel, M.C., Lowe, L., Srikanthan, R., McVicar, T.R. 2013. Estimating actual, potential, reference crop and pan evaporation using standard meteorological data: a pragmatic synthesis. Hydrology & Earth System Sciences 17, 1331–1363. doi:10.5194/hess-17-1331-2013.