# ET.MortonCRWE

##### Morton CRWE Formulation

Implementing the Morton CRWE formulation for estimating potential evapotranspiration or shallow lake evaporation.

##### Usage

```
# S3 method for MortonCRWE
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 CRWE formulation:

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

`constants`

consists of constants required for the calculation of Morton CRWE 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 = 25.0 Wm^-2.mbar^-1 for T >= 0 degree Celcius, and = 28.75 Wm^-2.mbar^-1 for T >= 0 degree Celcius for CRWE model (Morton, 1986),*b0*- A constants in Morton's procedure, = 1.12 for CRWE model, (Morton, 1986)*b1*- A constant in Morton's procedure, = 13 for CRWE model (Morton, 1986),*b2*- A constant in Morton's procedure, = 1.12 for CRWE model (Morton, 1986),*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`

or`shallow lake ET`

:`potential ET`

proceeds to estimating potential evapotranspiration;`shallow lake ET`

proceeds to estimating shallow lake evaporation. 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_MortonCRWE.csv* in the working directory:

Daily aggregated estimations of MortonCRWE potential evapotranspiration or shallow lake evaporation.

Monthly aggregated estimations of MortonCRWE potential evapotranspiration or shallow lake evaporation.

Annually aggregated estimations of MortonCRWE potential evapotranspiration or shallow lake evaporation.

Monthly averaged estimations of daily MortonCRWE potential evapotranspiration or shallow lake evaporation.

Annually averaged estimations of daily MortonCRWE potential evapotranspiration or shallow lake evaporation.

Name of the formulation used which equals to `MortonCRWE`

.

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

or `Shallow Lake Evaporation`

.

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 lake evaporation*. Journal of Hydrology, vol. 66, no. 1-4, pp. 77-100.

##### See Also

##### Examples

```
# NOT RUN {
# Use processed existing data set and constants from
# kent Town, Adelaide
data("processeddata")
data("constants")
# Call ET.MortonCRWE under the generic function ET
results <- ET.MortonCRWE(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)*