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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