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# i.evapo.pt.1grass - Man Page

Computes evapotranspiration calculation Priestley and Taylor formulation, 1972.

## Keywords

imagery, evapotranspiration

## Synopsis

`i.evapo.pti.evapo.pt --helpi.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

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

soil_heatflux=nameÂ [required]

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

air_temperature=nameÂ [required]

Name of input air temperature raster map [K]

atmospheric_pressure=nameÂ [required]

Name of input atmospheric pressure raster map [millibars]

priestley_taylor_coeff=floatÂ [required]

Priestley-Taylor coefficient
Default: 1.26

output=nameÂ [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.

## Author

Yann Chemin, GRASS Development Team, 2007-08

## Source Code

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

Accessed: Tuesday May 14 13:41:41 2024

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Â© 2003-2024 GRASS Development Team, GRASS GIS 8.3.2 Reference Manual

## Info

GRASS 8.3.2 GRASS GIS User's Manual