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i.evapo.pt(1grass)

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_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

AUTHOR

Yann Chemin, GRASS Development Team, 2007-08

SOURCE CODE

Available at: i.evapo.pt source code (history)

Accessed: Monday Jun 01 16:58:11 2026

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GRASS 8.4.2