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Last data update: 2014.03.03

R: Priestley-Taylor Potential Evapotranspiration from...

PET_fromTemp

R Documentation

Priestley-Taylor Potential Evapotranspiration from temperature

Description

Calculates potential Evapotranspiration (in meters) based on the Priestley-Taylor equation (1972). We use an estimation of net radiation based on temperature data.

Usage

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"))

Arguments

`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)

Value

PET (potential evapotranspiration) in m

Note

We are assuming that the Ground heat flux on a daily time-step is zero

Author(s)

Josephine Archibald, M. Todd Walter

References

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

Examples

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)

Results


R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.

R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.

Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.

> library(EcoHydRology)
Loading required package: operators

Attaching package: 'operators'

The following objects are masked from 'package:base':

    options, strrep

Loading required package: topmodel
Loading required package: DEoptim

DEoptim package
Differential Evolution algorithm in R
Authors: D. Ardia, K. Mullen, B. Peterson and J. Ulrich

Loading required package: XML
> png(filename="/home/ddbj/snapshot/RGM3/R_CC/result/EcoHydRology/PET_fromTemp.Rd_%03d_medium.png", width=480, height=480)
> ### Name: PET_fromTemp
> ### Title: Priestley-Taylor Potential Evapotranspiration from temperature
> ### Aliases: PET_fromTemp
> 
> ### ** Examples
> 
> data(OwascoInlet)
> head(OwascoInlet)
        date  P_mm Streamflow_m3s baseflow_m3s Tmax_C Tmin_C
1 2009-04-22 4.318           3.77    0.0000000  17.78   3.89
2 2009-04-23 3.302           4.08    0.2943750  10.56   1.67
3 2009-04-24 0.254           3.65    0.5621719  10.00  -2.22
4 2009-04-25 0.000           3.23    0.7780090  24.44  -1.11
5 2009-04-26 0.000           2.97    0.9521583  30.56  11.11
6 2009-04-27 0.000           2.80    1.0971214  28.33  10.00
> 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)
> 
> 
> 
> 
> 
> 
> dev.off()
null device 
          1 
>