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crop_water_need

Compute "crop water need", the quantity of water needed to attain maximum crop productivity.

Available in version 6.4.0 and later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/crop.ncl"  ; This library is automatically loaded
                                                      ; from NCL V6.5.0 onward.
                                                      ; No need for user to explicitly load.

	function crop_water_need (
		pet         : numeric,  
		act_evaptr  : numeric,  
		opt     [1] : logical   
	)

Arguments

pet

Potential evapotranspiration. See: thornthwaite

act_evaptr

Actual evapotranspiration: the amount of water that is actually removed from a surface due to the processes of evaporation and transpiration. Same units, size, shape and type as pet.

opt

Currently not used. Set to False.

Return value

An array with the same dimensionality and type as pet containing the desired quantity.

Description

Here, this is simply:

    crop_water_need = pet - act_evaptr

All appropriate metadata is returned.

References: Actual, Reference and Potential Evapotranspiration

   Jeff Andresen, and Aaron Pollyea, Michigan State University Extension
   What is evapotranspiration and why it matters
   WWW: http://msue.anr.msu.edu/news/what_is_evapotranspiration_and_why_it_matters

   C. Brouwer and M. Heibloem (1986)
   Irrigation Water Management: Irrigation Water Needs
   WWW: http://www.fao.org/docrep/s2022e/s2022e00.htm
   
   Pidwirny, M. (2006).
   Actual and Potential Evapotranspiration
   Fundamentals of Physical Geography, 2nd Edition.
   WWW: http://www.physicalgeography.net/fundamentals/8j.html

   Irmak, S. and D.Z. Haman (2014; most recent)
   Evapotranspiration: Potential or Reference?
   WWW: https://edis.ifas.ufl.edu/ae256

Examples

Example 1: This is a bogus example. The actual evapotranspiration values are randomly created. The actual evapotranspiration may exceed those estimated by the thornthwaite function.

No examples are currently available for this function.

   tmp           = (/23.3, 21.1, 19.6, 17.2, 12.6, 10.9 \
                    ,10.0, 11.0, 13.0, 15.8, 17.8, 20.1/)
   tmp@units     = "degC"
   tmp@long_name = "Sellers, Physical Climatology; 1969, p173"

   latAsp        = -38.0                                 ; Latitude of Aspendale, Australia
   pet           = thornthwaite(tmp, latAsp, False, 0)
   pet@long_name = "PET: Aspendale, Australia"
   pet@units     = "mm/month"                            ; ie, monthly total


   act_evap      = random_uniform(0.75,1.1,dimsizes(tmp))*pet
   cwn           = crop_water_need(pet, act_evap, False)
   printVarSummary(cwn)

   
   print("")
   print(pet+"  "+act_evap+"  "+cwn)

The edited output is: