Evapotranspiration.GrangerGray: Granger-Gray Formulation

Description

Implementing the Granger-Gray formulation for estimating actual areal evapotranspiration.

Usage

## S3 method for class 'GrangerGray':
Evapotranspiration(data, constants, solar, windfunction_ver, alpha, \dots)

Arguments

data

A list of data in class "GrangerGray" which contains the following items (climate variables) required by Granger-Gray 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 Granger-Gray 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^

solar

Must be either "data", "sunshine hours", "cloud" or "monthly precipitation". "data" indicates that solar radiation data is to be used to calculate evapotranspiration; "sunshine hours" indicates that solar radiation is to be calculated using the real data

windfunction_ver

The version of Penman wind function that will be used within the Penman formulation. Must be either "1948" or "1956". "1948" is for applying the Penman's 1948 wind function (Penman, 1948); "1956" is for applying the Penman's 1956 wind function (Penman, 19

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 GrangerGray. Such objects are list with components:
PET.DailyA zoo object containing daily aggregated estimations of Granger-Gray actual areal evapotranspiration.
PET.MonthlyA zoo object containing monthly aggregated estimations of Granger-Gray actual areal evapotranspiration.
PET.AnnualA zoo object containing annually aggregated estimations of Granger-Gray actual areal evapotranspiration.
PET.MonthlyAveA zoo object containing monthly averaged estimations of daily Granger-Gray actual areal evapotranspiration.
PET.AnnualAveA zoo object containing annually averaged estimations of daily Granger-Gray actual areal evapotranspiration.
PET_formulationA character string containing the name of the formulation used which equals to "Granger-Gray".
PET_typeA character string containing the type of the estimation obtained which is "Actual Areal Evapotranspiration".
message1A message to inform the users about how solar radiation has been calculated by using which data.
message2A message to inform the users about which version of the Penman wind function has been used.

Details

The alternative calculation options can be selected through arguments solar and windfunction_ver, 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. PENMAN, H. L. 1948. Natural evaporation from open water, bare soil and grass. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 193, 120-145. PENMAN, H. L. 1956. Evaporation: An introductory survey. Netherlands Journal of Agricultural Science, 4, 9-29.

Examples

Run this code

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

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

# Call generic function Evapotranspiration(data, ...) with class "GrangerGray"
results <- Evapotranspiration(data, constants, solar="sunshine hours", windfunction_ver = 
"1948", alpha = 0.23)

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