Implementing the Abtew formulation for estimating actual evapotranspiration.
Usage
## S3 method for class 'Abtew'
ET(data, constants, ts="daily", solar="sunshine hours",...)
Arguments
data
A list of data in class "Abtew" which contains the following items (climate variables) required by Abtew formulation: Tmax, Tmin, Rs or n or Cd
constants
A list named constants consists of constants required for the calculation of Abtew formulation which must contain the following items: Elev - ground elevation above mean sea level in m, lambda - latent heat of vaporisation = 2.45 MJ.kg^-1, lat_rad - latitude in radians, Gsc - solar constant = 0.0820 MJ.m^-2.min^-1, sigma - Stefan-Boltzmann constant = 4.903*10^-9 MJ.K^-4.m^-2.day^-1.
The following constants are also required when argument solar has value of sunshine hours: as - fraction of extraterrestrial radiation reaching earth on sunless days, bs - difference between fracion of extraterrestrial radiation reaching full-sun days and that on sunless days.
ts
Must be either daily, monthly or annual, which indicates the disired time step that the output ET estimates should be on.
Default is daily.
solar
Must be either data, sunshine hours, cloud or monthly precipitation: data indicates that solar radiation data is to be used directly for calculating evapotranspiration; sunshine hours indicates that solar radiation is to be calculated using the real data of sunshine hours; cloud sunshine hours is to be estimated from cloud data; monthly precipitation indicates that solar radiation is to be calculated directly from monthly precipitation.
Default is sunshine hours.
...
Dummy for generic function, no need to define.
Details
The alternative calculation options can be selected through argument solar, please see Arguments for details.
Value
The function prints a calculation summary to the screen containing the following elements:
- ET model name and ET quantity estimated
- Option for calculating solar radiation (i.e. the value of argument solar)
- Time step of the output ET estimates (i.e. the value of argument ts)
- Units of the output ET estimates
- Time duration of the ET estimation
- Number of ET estimates obtained in the entire time-series
- Basic statistics of the estimated ET time-series including mean, max and min values.
The function also generates a list containing the following components, which is saved into a csv file named as ET_Abtew.csv in the working directory:
ET.Daily
Daily aggregated estimations of Abtew actual evapotranspiration.
ET.Monthly
Monthly aggregated estimations of Abtew actual evapotranspiration.
ET.Annual
Annually aggregated estimations of Abtew actual evapotranspiration.
ET.MonthlyAve
Monthly averaged estimations of daily Abtew actual evapotranspiration.
ET.AnnualAve
Annually averaged estimations of daily Abtew actual evapotranspiration.
ET_formulation
Name of the formulation used which equals to Abtew.
ET_type
Type of the estimation obtained which is Actual Evapotranspiration.
message1
A message to inform the users about how solar radiation has been calculated by using which data.
Author(s)
Danlu Guo
References
Abtew, W. 1996. Evapotranspiration measurements and modeling for three wetland systems in south florida. Wiley Online Library.
See Also
ET,data,defaultconstants,constants
Examples
# Use processed existing data set and constants from kent Town, Adelaide
data("processeddata")
data("constants")
# Call ET.Abtew under the generic function ET
results <- ET.Abtew(data, constants,ts="daily", solar="sunshine hours")
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(Evapotranspiration)
Loading required package: zoo
Attaching package: 'zoo'
The following objects are masked from 'package:base':
as.Date, as.Date.numeric
> png(filename="/home/ddbj/snapshot/RGM3/R_CC/result/Evapotranspiration/ET.Abtew.Rd_%03d_medium.png", width=480, height=480)
> ### Name: ET.Abtew
> ### Title: Abtew Formulation
> ### Aliases: ET.Abtew
> ### Keywords: Abtew evapotranspiration actual evapotranspiration
>
> ### ** Examples
>
> # Use processed existing data set and constants from kent Town, Adelaide
> data("processeddata")
> data("constants")
>
> # Call ET.Abtew under the generic function ET
> results <- ET.Abtew(data, constants,ts="daily", solar="sunshine hours")
Abtew Actual ET
Sunshine hour data have been used for calculating incoming solar radiation
Timestep: daily
Units: mm
Time duration: 2001-03-01 to 2004-08-31
1280 ET estimates obtained
Basic stats
Mean: 3.41
Max: 5.61
Min: 1.55
>
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> dev.off()
null device
1
>
providing 
.