Scroll to navigation GRASS GIS User's Manual

NAME - Computes evapotranspiration calculation Priestley and Taylor formulation, 1972.


imagery, evapotranspiration

SYNOPSIS --help [-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


Name of input net radiation raster map [W/m2]

Name of input soil heat flux raster map [W/m2]

Name of input air temperature raster map [K]

Name of input atmospheric pressure raster map [millibars]

Priestley-Taylor coefficient
Default: 1.26

Name of output evapotranspiration raster map [mm/d]

DESCRIPTION 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.time, i.eb.netrad, r.sun


Yann Chemin, GRASS Development Team, 2007-08


Available at: source code (history)

Main index | Imagery index | Topics index | Keywords index | Graphical index | Full index

© 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual

GRASS 7.8.5