i.evapo.ptgrass - Online in the Cloud

PROGRAM:

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.

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