Evapotranspiration.ChapmanAustralian: Chapman Formulation

Description

Implementing the Chapman formulation for estimating equivalent Penmen-Monteith reference crop evapotranspiration.

Usage

## S3 method for class 'ChapmanAustralian':
Evapotranspiration(data, constants, Penpan, sunshine.hours, alpha, \dots)

Arguments

data

A list of data in class "ChapmanAustralian" which contains the following items (climate variables) required by Chapman formulation: "Epan" or "Ta" and "Tmax" and "Tmin" and "vabar" and "vas" and "u2" or "uz" and "n" or "Cd"

constants

A list named "constants" consists of constants required for the calculation of Penman 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,

Penpan

Must be TRUE or FALSE, indicating if the Penpan formulation is used for estimating Class-A pan evaporation required in Chapman formulation. If TRUE Penpan will be used and if FALSE the actual data of Class-A pan evaporation will be used.

sunshine.hours

Must be either "data" or "cloud". "data" 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.

alpha

Must be defined if Penpan = TRUE. Any numeric value between 0 and 1 (dimensionless), albedo of evaporative surface (or surrounding surface for Penpan formulation) representing the portion of the incident radiation that is reflected back at the surface.

...

Dummy for generic function, no need to define.

Value

This function returns a object of class ChapmanAustralian. Such objects are list with components:
PET.DailyA zoo object containing daily aggregated estimations of Chapman equivalent Penmen-Monteith reference crop evapotranspiration.
PET.MonthlyA zoo object containing monthly aggregated estimations of Chapman equivalent Penmen-Monteith reference crop evapotranspiration.
PET.AnnualA zoo object containing annually aggregated estimations of Chapman equivalent Penmen-Monteith reference crop evapotranspiration.
PET.MonthlyAveA zoo object containing monthly averaged estimations of daily Chapman equivalent Penmen-Monteith reference crop evapotranspiration.
PET.AnnualAveA zoo object containing annually averaged estimations of daily Chapman equivalent Penmen-Monteith reference crop evapotranspiration.
PET_formulationA character string containing the name of the formulation used which equals to "Chapman".
PET_typeA character string containing the type of the estimation obtained which is "Equivalent Penmen-Monteith Reference Crop Evapotranspiration".
message1A message to inform the users about how solar radiation has been calculated by using which data.
message5A message to inform the users about if the Class-A pan evaporation is from actual data or from Penpan estimation.

Details

The alternative calculation options can be selected through arguments Penpan and sunshine.hours, please see "Arguments" for details.

References

MCMAHON, T., PEEL, M., LOWE, L., SRIKANTHAN, R. & MCVICAR, T. 2012. Estimating actual, potential, reference crop and pan evaporation using standard meteorological data: a pragmatic synthesis. Hydrology and Earth System Sciences Discussions, 9, 11829-11910.

Examples

Run this code

# Use processed existing data set from kent Town, Adelaide
data("processeddata")
data("constants")

# Set data class to be "ChapmanAustralian" to call function
funname <- "ChapmanAustralian" 
class(data) <- funname 

# Call generic function Evapotranspiration(data, ...) with class "ChapmanAustralian"
results <- Evapotranspiration(data, constants, Penpan = TRUE, sunshine.hours = "data", alpha = 0.23)

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