Evapotranspiration (version 1.7)

ET.BlaneyCriddle: Blaney-Criddle Formulation

Description

Implementing the Blaney-Criddle formulation for estimating reference crop evapotranspiration.

Usage

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

Arguments

data

A list of data in class "BlaneyCriddle" which contains the following items (climate variables) required by Blaney-Criddle formulation: "Tmax", "Tmin", "RHmin", "n", "u2" or "uz"

constants

A list named "constants" consists of constants required for the calculation of Blaney-Criddle formulation which must contain the following items: "Elev" - ground elevation above mean sea level in m, "lat_rad" - latitude in radians, "z" - height o

solar

Must be either "sunshine hours" or "cloud". "sunshine hours" indicates that solar radiation is to be calculated using the data of sunshine hours; for "cloud" sunshine hours is to be estimated from cloud data.

height

Must be TRUE or FALSE, indicating if adjustment for site elevation for arid and semi-arid regions is applied in Blaney-Criddle formulation (Allen and Brockway, 1983).

...

Dummy for generic function, no need to define.

Value

• This function returns a object of class BlaneyCriddle. Such objects are list with components:
• ET.Daily
  A zoo object containing daily aggregated estimations of Blaney-Criddle reference crop evapotranspiration.
• ET.Monthly
  A zoo object containing monthly aggregated estimations of Blaney-Criddle reference crop evapotranspiration.
• ET.Annual
  A zoo object containing annually aggregated estimations of Blaney-Criddle reference crop evapotranspiration.
• ET.MonthlyAve
  A zoo object containing monthly averaged estimations of daily Blaney-Criddle reference crop evapotranspiration.
• ET.AnnualAve
  A zoo object containing annually averaged estimations of daily Blaney-Criddle reference crop evapotranspiration.
• ET_formulation
  A character string containing the name of the formulation used which equals to "Blaney-Criddle".
• ET_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.
• message3
  A message to inform the users about if height adjustment has been applied to calculated Blaney-Criddle reference crop evapotranspiration.

Details

The alternative calculation options can be selected through argument solar, please see "Arguments" for details. Height adjustment for the estimations is 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. ALLEN, R. & PRUITT, W. 1986. Rational Use of The FAO Blaney-Criddle Formula. Journal of Irrigation and Drainage Engineering, 112, 139-155.

Examples

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

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

# Call generic function ET(data, ...) with class "BlaneyCriddle"
results <- ET(data, constants, solar="sunshine.hours", height = TRUE)