i.evapo.pt.1grass man page

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


imagery, evapotranspiration


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]


Set negative ETa to zero
Allow output files to overwrite existing files
Print usage summary
Verbose module output
Quiet module output
Force launching GUI dialog


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]


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.


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


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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