PET_fromTemp {EcoHydRology} | R Documentation |
Calculates potential Evapotranspiration (in meters) based on the Priestley-Taylor equation (1972). We use an estimation of net radiation based on temperature data.
PET_fromTemp(Jday, Tmax_C, Tmin_C, lat_radians, AvgT = (Tmax_C + Tmin_C)/2, albedo = 0.18, TerrestEmiss = 0.97, aspect = 0, slope = 0, forest = 0, PTconstant=1.26, AEparams=list(vp=NULL, opt="linear"))
Jday |
Day of the year |
Tmax_C |
Maximum daily temperature (degrees C) |
Tmin_C |
Minimum daily temperature (degrees C) |
lat_radians |
latitude (radians = decimal degrees*pi/180) |
AvgT |
Average daily temperature (degrees C) (if not known, will be taken as the averages of the daily extremes) |
albedo |
(-) average surface albedo. Can be expressed as a single value, or as a vector with the same length as Jday, Tmax_C and Tmin_C |
TerrestEmiss |
(-) Surface Emissivity - defaults to 0.97 |
aspect |
(radians) Surface aspect |
slope |
(radians) average slope |
forest |
(-) Forest or shade cover (0-1). This modifies the amount of solar radiation reaching the location of interest. It should always set to zero for landscape-wide processes regardless of the amount of forest present. Only change this if calculating PET under a canopy. |
PTconstant |
(-) Priestley-Taylor Constant, often 1.26 |
AEparams |
Atmospheric Emissivity options. Defaults to linear approximation. To use Brutsaert option, include vapor pressure values (kPa) |
PET (potential evapotranspiration) in m
We are assuming that the Ground heat flux on a daily time-step is zero
Josephine Archibald, M. Todd Walter
Archibald, J.A. and M. T. Walter, 2013. Do energy-based PET models require more input data than T-based models? - An evaluation at four humid FluxNet sites. Journal of the American Water Resources Association (JAWRA)
Brutsaert, W., 1975. On a Derivable Formula for Long-Wave Radiation from Clear Skies. Water Resources Research 11(5):742-744.
Priestley and Taylor, 1972. On the assessment of surface heat flux and evaporation using large-scale parameters. Mon. Weath. Rev. 100: 81-92
## Not run: data(OwascoInlet) head(OwascoInlet) attach(OwascoInlet) PETapprox <- PET_fromTemp(Jday=(1+as.POSIXlt(date)$yday), Tmax_C=Tmax_C, Tmin_C=Tmin_C, lat_radians=42.45*pi/180) plot(PETapprox*1000~date, type="l") detach(OwascoInlet) ## End(Not run)