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.

AUTHORS

Yann Chemin, GRASS Development Team, 2007-08

SOURCE CODE

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