NAME

       i.evapo.pt   -  Computes  evapotranspiration calculation Priestley and Taylor formulation,
       1972.

KEYWORDS

       imagery, evapotranspiration

SYNOPSIS

       i.evapo.pt
       i.evapo.pt --help
       i.evapo.pt     [-z]     net_radiation=name     soil_heatflux=name     air_temperature=name
       atmospheric_pressure=name    priestley_taylor_coeff=float    output=name     [--overwrite]
       [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -z
           Set negative ETa to zero

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       net_radiation=name [required]
           Name of input net radiation raster map [W/m2]

       soil_heatflux=name [required]
           Name of input soil heat flux raster map [W/m2]

       air_temperature=name [required]
           Name of input air temperature raster map [K]

       atmospheric_pressure=name [required]
           Name of input atmospheric pressure raster map [millibars]

       priestley_taylor_coeff=float [required]
           Priestley-Taylor coefficient
           Default: 1.26

       output=name [required]
           Name of output evapotranspiration raster map [mm/d]

DESCRIPTION

       i.evapo.pt Calculates the diurnal evapotranspiration after Prestley and Taylor (1972). The
       Priestley-Taylor  model  (Priestley and Taylor, 1972) is a modification of Penman’s more
       theoretical equation.

NOTES

       RNETD optional output from  i.evapo.potrad  is  giving  good  results  as  input  for  net
       radiation in this module.

       Alpha values:

           •   1.32  for  estimates  from  vegetated areas as a result of the increase in surface
               roughness (Morton, 1983; Brutsaert and Stricker, 1979)

           •   1.26 is applicable in humid climates (De Bruin  and  Keijman,  1979;  Stewart  and
               Rouse, 1976; Shuttleworth and Calder, 1979), and temperate hardwood swamps (Munro,
               1979)

           •   1.74 has been recommended for estimating potential evapotranspiration in more arid
               regions (ASCE, 1990). This worked well in Greece with University of Thessaloniki.
       Alpha values extracted from: Watflood manual.

SEE ALSO

        i.evapo.mh, i.evapo.pm, i.evapo.time, i.eb.netrad, r.sun

AUTHORS

       Yann Chemin, GRASS Development team, 2007-08

       Last changed: $Date: 2014-12-09 18:31:29 +0100 (Tue, 09 Dec 2014) $

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