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_)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).
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.