Evapotranspiration (version 1.7)

ET.PriestleyTaylor: Priestley-Taylor Formulation

Description

Implementing the Priestley-Taylor formulation for potential evaporation

Usage

## S3 method for class 'PriestleyTaylor':
ET(data, constants, solar, alpha, \dots)

Arguments

data

A list of data in class "PriestleyTaylor" which contains the following items (climate variables) required by Priestley-Taylor formulation: "Tmax", "Tmin", "RHmax", "RHmin", "RS", "n" or "Cd"

constants

A list named "constants" consists of constants required for the calculation of Priestley-Taylor formulation which must contain the following items: "Elev" - ground elevation above mean sea level in m, "lambda" - latent heat of vaporisation = 2.45 MJ

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 th

alpha

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 PriestleyTaylor. Such objects are list with components:
• ET.Daily
  A zoo object containing daily aggregated estimations of Priestley-Taylor potential evaporation.
• ET.Monthly
  A zoo object containing monthly aggregated estimations of Priestley-Taylor potential evaporation.
• ET.Annual
  A zoo object containing annually aggregated estimations of Priestley-Taylor potential evaporation.
• ET.MonthlyAve
  A zoo object containing monthly averaged estimations of daily Priestley-Taylor potential evaporation.
• ET.AnnualAve
  A zoo object containing annually averaged estimations of daily Priestley-Taylor potential evaporation.
• ET_formulation
  A character string containing the name of the formulation used which equals to "Priestley-Taylor".
• ET_type
  A character string containing the type of the estimation obtained which is "Potential Evaporation".
• message1
  A message to inform the users about how solar radiation has been calculated by using which data.

Details

The alternative calculation options can be selected through argument solar, please see "Arguments" for details. User-defined evaporative surface is allowed through argument alpha, 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

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

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

# Call generic function ET(data, ...) with class "PriestleyTaylor"
results <- ET(data, constants, solar="sunshine hours", alpha = 0.08)