i.evapo.pt(1grass) GRASS GIS User's Manual i.evapo.pt(1grass)
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_tempera-
ture=name atmospheric_pressure=name priestley_taylor_coeff=float out-
put=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 in-
put for net radiation in this module.
Alpha values:
• 1.32 for estimates from vegetated areas as a result of the in-
crease 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 evapotran-
spiration 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
SOURCE CODE
Available at: i.evapo.pt source code (history)
Accessed: unknown
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