Evapotranspiration (version 1.0)

Evapotranspiration.MattShuttleworth: Matt-Shuttleworth Formulation

Description

Implementing the Matt-Shuttleworth formulation for reference crop evapotranspiration

Usage

## S3 method for class 'MattShuttleworth':
Evapotranspiration(data, constants, sunshine.hours, alpha, r_s, CH, \dots)

Arguments

data

A list of data in class "MattShuttleworth" which contains the following items (climate variables) required by Matt-Shuttleworth formulation: "Ta", "vas", vabar", Tmax", "Tmin", "n" or "Cd" or "Precip", "u2" or "uz"

constants

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

sunshine.hours

Must be either "data", "cloud" or "monthly precipitation". "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; "monthly precipitation" indicates that s

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.

r_s

Any value (seconds per metre), surface resistance depends on the type of reference crop.

CH

Any value (metres), crop height depends on the reference crop.

...

Dummy for generic function, no need to define.

Value

• This function returns a object of class MattShuttleworth. Such objects are list with components:
• PET.Daily
  A zoo object containing daily aggregated estimations of Matt-Shuttleworth reference crop evapotranspiration.
• PET.Monthly
  A zoo object containing monthly aggregated estimations of Matt-Shuttleworth reference crop evapotranspiration.
• PET.Annual
  A zoo object containing annually aggregated estimations of Matt-Shuttleworth reference crop evapotranspiration.
• PET.MonthlyAve
  A zoo object containing monthly averaged estimations of daily Matt-Shuttleworth reference crop evapotranspiration.
• PET.AnnualAve
  A zoo object containing annually averaged estimations of daily Matt-Shuttleworth reference crop evapotranspiration.
• PET_formulation
  A character string containing the name of the formulation used which equals to "Matt-Shuttleworth".
• PET_type
  A character string containing the type of the estimation obtained which is "Reference Crop Evapotranspiration".
• 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 sunshine.hours, please see "Arguments" for details. User-defined evaporative surface is allowed through arguments alpha, r_s and CH, please see "Arguments" for details.

References

SHUTTLEWORTH, W. & WALLACE, J. 2009. Calculating the water requirements of irrigated crops in Australia using the Matt-Shuttleworth approach. Transactions of the ASABE, 52, 1895-1906. 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 "MattShuttleworth" to call function
funname <- "MattShuttleworth"
class(data) <- funname

# Call generic function Evapotranspiration(data, ...) with class "MattShuttleworth"
results <- Evapotranspiration(data, constants, sunshine.hours="data", alpha = 0.23, r_s = 70, CH = 
0.12)