Implementing the Turc formulation for estimating reference crop evapotranspiration.
# S3 method for Turc
ET(data, constants, ts="daily", solar="sunshine hours", humid= F,
message="yes", AdditionalStats="yes", save.csv="yes", …)A list of data which contains the following items (climate variables) required by Turc formulation: Tmax, Tmin (degree Celcius), Rs (Megajoules per sqm) or n (hour) or Cd (okta)
A list named constants consists of constants required for the calculation of Turc 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,
lat_rad - latitude in radians,
Gsc - solar constant = 0.0820 MJ.m^-2.min^-1,
sigma - Stefan-Boltzmann constant = 4.903*10^-9 MJ.K^-4.m^-2.day^-1.
The following constants are also required when argument solar has value of sunshine hours:
as - fraction of extraterrestrial radiation reaching earth on sunless days,
bs - difference between fracion of extraterrestrial radiation reaching full-sun days and that on sunless days.
Must be either daily, monthly or annual, which indicates the disired time step that the output ET estimates should be on.
Default is daily.
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 the real data of sunshine hours;
cloud sunshine hours is to be estimated from cloud data;
monthly precipitation indicates that solar radiation is to be calculated directly from monthly precipitation.
Default is sunshine hours.
Must be T or F, indicating if adjustment for non-humid conditions is applied in Turc formulation (Alexandris et al., 2008, Equation 5b).
Default is F for no adjustment.
Must be either yes or no, indicating whether message should be printed for calculation summary including the following elements:
- ET model name and ET quantity estimated
- Evaporative surface
- Option for calculating solar radiation (i.e. the value of argument solar)
- if adjustment for non-humid conditions has been applied (i.e. the value of argument humid)
- Time step of the output ET estimates (i.e. the value of argument ts)
- Units of the output ET estimates
- Time duration of the ET estimation
- Number of ET estimates obtained in the entire time-series
- Basic statistics of the estimated ET time-series including mean, max and min values.
"yes" or "no" indicating whether monthly averaged and annual averaged ET should be calculated.
Must be either yes or no, indicating whether a .csv of ET estimates should be saved to working directory.
Dummy for generic function, no need to define.
The function generates a list containing the following components:
Daily aggregated estimations of Turc reference crop evapotranspiration.
Monthly aggregated estimations of Turc reference crop evapotranspiration.
Annually aggregated estimations of Turc reference crop evapotranspiration.
Monthly averaged estimations of daily Turc reference crop evapotranspiration.
Annually averaged estimations of daily Turc reference crop evapotranspiration.
Name of the formulation used which equals to Turc.
Type of the estimation obtained which is Reference Crop Evapotranspiration.
A message to inform the users about how solar radiation has been calculated by using which data.
A message to inform the users about if adjustment for non-humid conditions has been applied to calculated Turc reference crop evapotranspiration.
The alternative calculation options can be selected through argument solar, please see Arguments for details.
Humidity adjustment for the estimations is available through argument humid, please see Arguments for details.
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.
Turc, L. 1961, Estimation of irrigation water requirements, potential evapotranspiration: a simple climatic formula evolved up to date. Ann. Agron, vol. 12, no. 1, pp. 13-49.
Alexandris, S., Stricevic, R.Petkovic, S. 2008, Comparative analysis of reference evapotranspiration from the surface of rainfed grass in central Serbia, calculated by six empirical methods against the Penman-Monteith formula. European Water, vol. 21, no. 22, pp. 17-28.
# NOT RUN {
# Use processed existing data set and constants from kent Town, Adelaide
data("processeddata")
data("constants")
# Call ET.Turc under the generic function ET
results <- ET.Turc(data, constants, ts="daily", solar="sunshine hours", humid= FALSE,
message="yes", AdditionalStats="yes", save.csv="yes")
# }
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