Blaney-Criddle Formulation

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Description

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

Usage

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## S3 method for class 'BlaneyCriddle'
ET(data, constants, ts="daily", solar="sunshine hours", height = F , ...) 

Arguments

data

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

constants

A list named constants consists of constants required for the calculation of PenPan 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,
z - height of wind instrument in m,
e0,e1,e2,e3,e4 - recommended values of 0.81917, -0.0040922, 1.0705, 0.065649, -0.0059684, -0.0005967 respectively (Table 1 in Frevert et al., 1983).

ts

Must be either daily, monthly or annual, which indicates the disired time step that the output ET estimates should be on. Default is daily.

solar

Must be either \codesunshine hours or cloud:
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.
Default is sunshine hours.

height

Must be T or F, indicating if adjustment for site elevation for arid and semi-arid regions is applied in Blaney-Criddle formulation (Allen and Brockway, 1983).
Default is F for no adjustment.

...

Dummy for generic function, no need to define.

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.

Value

The function prints a calculation summary to the screen containing 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 height adjustment has been applied on results (i.e. the value of argument height)
- 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_BlaneyCriddle.csv in the working directory:

ET.Daily

Daily aggregated estimations of Blaney-Criddle reference crop evapotranspiration.

ET.Monthly

Monthly aggregated estimations of Blaney-Criddle reference crop evapotranspiration.

ET.Annual

Annually ggregated estimations of Blaney-Criddle reference crop evapotranspiration.

ET.MonthlyAve

Monthly averaged estimations of daily Blaney-Criddle reference crop evapotranspiration.

ET.AnnualAve

Annually averaged estimations of daily Blaney-Criddle reference crop evapotranspiration.

ET_formulation

Name of the formulation used which equals to Blaney-Criddle.

ET_type

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.

Author(s)

Danlu Guo

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.G.Brockway, C.E. 1983, Estimating consumptive use on a statewide basis. Advances in Irrigation and Drainage@ sSurviving External Pressures, ASCE, pp. 79-89.

Allen, R. & Pruitt, W. 1986. Rational Use of The FAO Blaney-Criddle Formula. Journal of Irrigation and Drainage Engineering, 112, 139-155.

Frevert, D.K., Hill, R.W.Braaten, B.C. 1983, Estimation of FAO evapotranspiration coefficients, Journal of Irrigation and Drainage Engineering, vol. 109, no. 2, pp. 265-270.

See Also

ET,data,defaultconstants,constants

Examples

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

# Call ET.BlaneyCriddle under the generic function ET
results <- ET.BlaneyCriddle(data, constants, ts="daily", solar="sunshine hours", height= FALSE)

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