PE_Oudin.Rd

\encoding{UTF-8}


\name{PE_Oudin}
\alias{PE_Oudin}


\title{Computation of daily our hourly series of potential evapotranspiration with Oudin's formula}


\usage{
PE_Oudin(JD, Temp, LatRad, Lat, LatUnit, TimeStepIn = "daily", TimeStepOut = "daily")
}


\arguments{
\item{JD}{[numeric] time series of Julian day of the year [-]; see details below}

\item{Temp}{[numeric] time series of daily (or hourly) mean air temperature [°C]}

\item{LatRad}{(deprecated)[numeric] latitude of measurement for the temperature series [rad]. Please use \code{Lat} instead}

\item{Lat}{[numeric] latitude of measurement for the temperature series [radian or degrees]}

\item{LatUnit}{[character] latitude unit (default = \code{"rad"} or \code{"deg"})}

\item{TimeStepIn}{[character] time step of inputs (default = \code{"daily"} or \code{"hourly"})}

\item{TimeStepOut}{[character] time step of outputs (default = \code{"daily"} or \code{"hourly"})}
}


\value{
[numeric] time series of daily potential evapotranspiration [mm/time step]
}


\description{
Function which computes daily PE using the formula from Oudin et al. (2005).
From daily to hourly time steps, the PE is disaggregated as explained by Lobligeois (2014; p. 78)
}

\details{
In the \code{JD} argument, the Julian day of the year of the 1st of January is equal to 1 and the 31st of December to 365 (366 in leap years)). If the Julian day of the year is computed on an object of the \code{POSIXlt} class, the user has to add 1 to the returned value (e.g. \code{as.POSIXlt("2016-12-31")$yday + 1}).
For hourly temperature, all the values of the same day have to be set to the same Julian day of the year (e.g. \code{as.POSIXlt("2016-12-31 00:00:00")$yday + 1} and \code{as.POSIXlt("2016-12-31 00:01:00")$yday + 1}). Each days must have 24 identical Julian day values (one for each hour).
}

\examples{
library(airGR)
data(L0123001)
PotEvap <- PE_Oudin(JD = as.POSIXlt(BasinObs$DatesR)$yday + 1,
                         Temp = BasinObs$T,
                         Lat = 0.8, LatUnit = "rad")
}


\author{
Laurent Coron, Ludovic Oudin, Olivier Delaigue, Guillaume Thirel
}


\references{
Oudin, L., F. Hervieu, C. Michel, C. Perrin, V. Andréassian, F. Anctil and C. Loumagne (2005). 
  Which potential evapotranspiration input for a lumped rainfall-runoff model?: 
  Part 2-Towards a simple and efficient potential evapotranspiration model for rainfall-runoff modelling. 
  Journal of Hydrology, 303(1-4), 290-306. doi:10.1016/j.jhydrol.2004.08.026.
Lobligeois, F. (2014).
  Mieux connaitre la distribution spatiale des pluies améliore-t-il la modélisation des crues ? Diagnostic sur 181 bassins versants français.
  PhD thesis (in French), AgroParisTech (Paris), IRSTEA (Antony), France.
}