# ET.MortonCRAE

##### Morton CRAE Formulation

Implementing the Morton CRAE formulation for estimating potential evapotranspiration, wet-environment areal evapotranspiration and actual areal evapotranspiration.

##### Usage

```
# S3 method for MortonCRAE
ET(data, constants, ts="monthly", est="potential ET",
solar="sunshine hours", Tdew= T, alpha = NULL, …)
```

##### Arguments

- data
A list of data which contains the following items (climate variables) required by Morton CRAE formulation:

*Tmax*,*Tmin*,*Tdew*,*Rs*or*n*or*Cd*- constants
A list named

`constants`

consists of constants required for the calculation of Morton CRAE formulation which must contain the following items:*Elev*- ground elevation above mean sea level in m,*lat_rad*- latitude in radians,*PA*- annual precipitation in mm, required when precipitation data is not available,*z*- height of wind instrument in m,*sigma*- Stefan-Boltzmann constant = 4.903*10^-9 MJ.K^-4.m^-2.day^-1,*lat*- latitude in degrees,*epsilonMo*- surface emissivity = 0.92 (Morton, 1986),*fz*- A constant in Morton's procedure = 28.0 Wm^-2.mbar^-1 for T >= 0 degree Celcius, and = 28.0*1.15 Wm^-2.mbar^-1 for T >= 0 degree Celcius for CRAE model (Morton, 1983),*b0*- a constants in Morton's procedure, = 1 for CRAE model (Morton, 1983),*b1*- a constant in Morton's procedure, = 14 for CRAE model (Morton, 1983),*b2*- a constant in Morton's procedure, = 1.2 for CRAE model (Morton, 1983),*gammaps*- Produce of Psychrometric constant and atmospheric pressure as sea level, = 0.66 mbar. degree Celcius^-1 for T >= 0 degree Celcius, = 0.66/1.15 mbar. degree Celcius^-1 for T < 0 degree Celcius (Morton, 1983),*alphaMo*- a constant in Morton's procedure, = 17.27 when T >= 0 degree Celcius, = 21.88 when T < 0 degree Celcius (Morton, 1983),*betaMo*- a constant in Morton's procedure, = 237.3 degree Celcius when T >= 0 degree Celcius, = 265.5 degree Celcius, when T < 0 degree Celcius (Morton, 1983),*sigmaMo*- Stefan-Boltzmann constant in Morton's procedure, = 5.67e-08 W.m^-2.K^-4 (Morton, 1983),*lambdaMo*- Latent heat of vaporisation in Morton's procedure, = 28.5W.day.kg^-1 when T >= 0 degree Celcius, = 28.5*1.15W.day.kg^-1 when T < 0 degree Celcius,- ts
Must be either

`monthly`

or`annual`

, which indicates the disired time step that the output ET estimates should be on. Default is`monthly`

.- 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 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`

.- est
Must be either

`potential ET`

,`wet areal ET`

or`actual areal ET`

:`potential ET`

proceeds to estimating potential evapotranspiration;`wet areal ET`

proceeds to estimating wet-environmental areal evapotranspiration;`actual areal ET`

proceeds to estimating actual areal evapotranspiraion. Default is`potential ET`

.- Tdew
Must be

`T`

or`F`

, indicating if real data of dew point temperature is used for calculating the radiation in Morton's formulations, if`T`

the data will be used and if`F`

the dew point temperature will be calculated from data of daily vapour pressure. Default is`T`

for using actual dew point temperature data.- alpha
Only needed if argument

`solar`

has value of`data`

. Any numeric value between 0 and 1 (dimensionless), albedo of evaporative surface representing the portion of the incident radiation that is reflected back at the surface. Default is`NULL`

in line with the default use of sunshine hours to estimate solar radiation (i.e. argument`solar`

is`sunshine hours`

.- …
Dummy for generic function, no need to define.

##### Details

The type of evapotranspiration calculated can be selected through argument `est`

, please see `Arguments`

for details.
The alternative calculation options can be selected through argument `solar`

and `Tdew`

, please see `Arguments`

for details.

##### Value

The function prints a calculation summary to the screen containign the following elements:
- ET model name and ET quantity estimated (i.e. the value of argument `est`

)
- Option for calculating solar radiation (i.e. the value of argument `solar`

)
- If the actual dew point temperature data are used (i.e. the value of argument `Tdew`

)
- 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.

The function also generates a list containing the following components, which is saved into a `csv`

file named as *ET_MortonCRAE.csv* in the working directory:

Daily aggregated estimations of Morton CRAE potential evapotranspiration, wet-environment areal evapotranspiration or actual areal evapotranspiration.

Monthly aggregated estimations of Morton CRAE potential evapotranspiration, wet-environment areal evapotranspiration or actual areal evapotranspiration.

A `zoo`

object containing annually aggregated estimations of Morton CRAE potential evapotranspiration, wet-environment areal evapotranspiration or actual areal evapotranspiration.

A `zoo`

object containing monthly averaged estimations of daily Morton CRAE potential evapotranspiration, wet-environment areal evapotranspiration or actual areal evapotranspiration.

A `zoo`

object containing annually averaged estimations of daily Morton CRAE potential evapotranspiration, wet-environment areal evapotranspiration or actual areal evapotranspiration.

Name of the formulation used which equals to `MortonCRAE`

.

Type of the estimation obtained which is either `Potential Evapotranspiration`

, `Wet-environment Areal Evapotranspiration`

and `Actual Areal 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 actual dew point temperature has been used in the calculations or alternative calculations has been performed without dew point temperature data.

##### 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.

Morton, F.I. 1983, *Operational estimates of areal evapotranspiration and their significance to the science and practice of hydrology*. Journal of Hydrology, vol. 66, no. 1-4, pp. 1-76.

##### See Also

##### Examples

```
# NOT RUN {
# Use processed existing data set and constants from
# kent Town, Adelaide
data("processeddata")
data("constants")
# Call ET.MortonCRAE under the generic function ET
results <- ET.MortonCRAE(data, constants, ts="monthly",
est="potential ET", solar="sunshine hours", Tdew= TRUE,
alpha = NULL)
# }
```

*Documentation reproduced from package Evapotranspiration, version 1.10, License: GPL (>= 2)*