i.evapo.pt(1grass)

💖 i.evapo.pt — the GRASS manual, but make it make sense 💖

okay bestie, welcome to i.evapo.pt, part of the GRASS User's Manual. She computes evapotranspiration using the Priestley and Taylor formulation, 1972. 🌸

Keywords: imagery, evapotranspiration

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✨ SYNOPSIS ✨

like, here's how you actually call her:

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 — sets negative ETa to zero. bye, negativity 💅
• --overwrite — lets output files overwrite existing files, no cap
• --help — prints the usage summary
• --verbose — verbose module output
• --quiet — quiet module output
• --ui — forces the GUI dialog to launch

🦋 Parameters

• net_radiation=name [required] — name of the input net radiation raster map, measured in [W/m2]
• soil_heatflux=name [required] — name of the input soil heat flux raster map, in [W/m2]
• air_temperature=name [required] — name of the input air temperature raster map, in [K]
• atmospheric_pressure=name [required] — name of the input atmospheric pressure raster map, in [millibars]
• priestley_taylor_coeff=float [required] — the Priestley-Taylor coefficient. Default: 1.26
• output=name [required] — name of the output evapotranspiration raster map, in [mm/d]

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🌈 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. she's giving "Penman but make it simpler" and honestly? iconic. 👑

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💅 NOTES 💅

The RNETD optional output from i.evapo.potrad is giving good results as input for net radiation in this module. like, it's literally serving. ✨

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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👀 SEE ALSO 👀

i.evapo.mh, i.evapo.pm, i.evapo.time, i.eb.netrad, r.sun

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🫶 AUTHOR 🫶

Yann Chemin, GRASS Development Team, 2007-08

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🧚 SOURCE CODE 🧚

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

Latest change: Thursday Jun 26 21:25:27 2025 in commit: 3ec2b13945d963db69544e3fc9339fbff72f33f3

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

© 2003-2026 GRASS Development Team, GRASS 8.5.0 Reference Manual

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and that's the whole vibe bestie 💖 this was GRASS 8.5.0 energy, filed under i.evapo.pt(1grass) — slay, go compute some evapotranspiration 🦋✨