Evapotranspiration (version 1.7)

ET.Penpan: Penpan Formulation

Description

Implementing the Penpan formulation for Class-A pan evaporation.

Usage

## S3 method for class 'Penpan':
ET(data, constants, solar, alpha, est, pan_coeff=NULL, overest, \dots)

Arguments

data

A list of data in class "Penpan" which contains the following items (climate variables) required by Penpan formulation: "Tmax", "Tmin", "RHmax", "RHmin", "Rs", "n" or "Cd", "u2" or "uz"

constants

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

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.

overest

Must be TRUE or FALSE, indicating if adjustment for the overestimation (i.e. divided by 1.078) of Class-A pan evaporation for Australian data is applied in Penpan formulation.

est

Must be either "pan" or "potential ET" to specify if estimation for the Class-A pan evaporation or potential evapotranspriation is performed.

pan_coeff

Only required if est == "potential ET", which defines the pan coefficient.

...

Dummy for generic function, no need to define.

Value

• This function returns a object of class Penpan. Such objects are list with components:
• ET.Daily
  A zoo object containing daily aggregated estimations of Penpan Class-A pan evaporation.
• ET.Monthly
  A zoo object containing monthly aggregated estimations of Penpan Class-A pan evaporation.
• ET.Annual
  A zoo object containing annually aggregated estimations of Penpan Class-A pan evaporation.
• ET.MonthlyAve
  A zoo object containing monthly averaged estimations of daily Penpan Class-A pan evaporation.
• ET.AnnualAve
  A zoo object containing annually averaged estimations of daily Penpan Class-A pan evaporation.
• ET_formulation
  A character string containing the name of the formulation used which equals to "Penpan".
• ET_type
  A character string containing the type of the estimation obtained which is "Class-A Pan 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. Adjustment for overestimation on the estimations are available through argument height, 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. ROTSTAYN, L. D., RODERICK, M. L. & FARQUHAR, G. D. 2006. A simple pan-evaporation model for analysis of climate simulations: Evaluation over Australia. Geophysical Research Letters, 33.

Examples

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

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

# Call generic function ET(data, ...) with class "Penpan"
results <- ET(data, constants, solar="sunshine hours", alpha = 0.23, est = "potential ET", 
pan_coeff = 0.71, overest = TRUE)