Functions to calculate potential evapotranspiration using Penman or Penman-Monteith.
penman(latrad, elevation, slorad, asprad, J, Tmin, Tmax, RHmin, RHmax, R_s, u, z=2.0, z0 = 0.001, alpha = 0.08, windfun="1956") penmanmonteith(rc, elevation, Tmin, Tmax, RHmin, RHmax, Rn, u = NA)
Latitude in radians.
Elevation (in m).
Slope (in radians).
Aspect (in radians from North).
Julian day, number of days since January 1, 4713 BCE at noon UTC.
Maximum temperature (degrees Celsius).
Minimum temperature (degrees Celsius).
Minimum relative humidity (percent).
Maximum relative humidity (percent).
Solar radiation (MJ/m2).
With wind speed (m/s).
Wind measuring height (m).
Roughness height (m).
Wind speed function version, either "1948" or "1956".
Canopy vapour flux (stomatal) resistance (s·m-1).
Daily net radiation (MJ·m-2·day-1).
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)
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 and Earth System Sciences 17, 1331–1363. doi:10.5194/hess-17-1331-2013.
Potential evapotranspiration (in mm of water).