i.evapo.time(1)

📦
version 8.4.2 · 8 versions
, in fedora 44

💖 i.evapo.time 💖

okay bestie, welcome to i.evapo.time — manual section 1, part of GRASS GIS, and it's literally the module that does temporal integration of satellite ET actual (ETa) following the daily ET reference (ETo) from meteorological station(s). no cap. 🌸

✨ NAME ✨

i.evapo.time — computes temporal integration of satellite ET actual (ETa) following the daily ET reference (ETo) from meteorological station(s). it's giving "combine the satellite vibes with the weather-station vibes" and honestly? iconic. 👑

🏷️ KEYWORDS 🏷️

  • imagery
  • evapotranspiration

🦋 SYNOPSIS 🦋

i.evapo.time
i.evapo.time --help
i.evapo.time eta=name[,name,...] eta_doy=name[,name,...]
eto=name[,name,...] eto_doy_min=float start_period=float
end_period=float output=name  [--overwrite]  [--help]  [--verbose]
[--quiet]  [--ui]

🎀 Flags 🎀

  • --overwrite — lets your output files just go ahead and overwrite whatever's already there. permission granted, bestie 💅
  • --help — prints the usage summary so you're not out here guessing 🙈
  • --verbose — verbose module output, aka it tells you everything it's doing, main character energy ✨
  • --quiet — quiet module output. shhh. no notes, just results 🤫
  • --ui — forces the GUI dialog to launch, for when you want to click instead of type 🖱️

🌸 Parameters 🌸

  • eta=name[,name,...] — [required] the names of your satellite ETa raster maps, in [mm/d or cm/d] units. give it one or give it a whole list, comma-separated 🍓
  • eta_doy=name[,name,...] — [required] the names of your satellite ETa Day of Year (DOY) raster maps, range [0-400], units [-] (yes, unitless, she's just a number) 🔢
  • eto=name[,name,...] — [required] the names of your meteorological station ETo raster maps, range [0-400], in [mm/d or cm/d] 🌦️
  • eto_doy_min=float — [required] the value of DOY for ETo first day. like, day one. the origin story 📅
  • start_period=float — [required] the value of DOY for the first day of the period studied 🫶
  • end_period=float — [required] the value of DOY for the last day of the period studied 🏁
  • output=name — [required] the name for the output raster map. your beautiful creation 💖

💅 DESCRIPTION 💅

so i.evapo.time (also known as i.evapo.time_integration) integrates ETa in time following a reference ET — typically one that came from a set of meteorological stations dataset. that's the whole vibe.

The inputs, bestie:

  • ETa images
  • ETa images DOY (Day of Year)
  • ETo images
  • ETo DOYmin as a single value

The method (the way she works, fr fr):

  1. each ETa pixel is divided by the same day ETo and become ETrF
  2. each ETrF pixel is multiplied by the ETo sum for the representative days
  3. sum all n temporal [ETrF*ETo_sum] pixels to make a summed(ET) in [DOYmin;DOYmax]

representative days calculation: let assume i belongs to range [DOYmin;DOYmax]

DOYbeforeETa[i] = ( DOYofETa[i] - DOYofETa[i-1] ) / 2
DOYafterETa[i] = ( DOYofETa[i+1] - DOYofETa[i] ) / 2

math but make it fashion ✨🧮

📝 NOTES 📝

ETo images preparation: if you only have one meteorological station data set, the easiest way is:

n=0
for ETo_val in Eto[1] Eto[2] ...
do
    r.mapcalc "eto$n = $ETo_val"
    `expr n = n + 1`
done

with Eto[1], Eto[2], etc. being a simple copy and paste from your data file of all ETo values separated by an empty space from each other. yes, literally just yeet them in there 🍓

if you have several meteorological stations data, then you need to grid them by generating Thiessen polygons or using different interpolation methods for each day. more stations, more work, that's the deal 🗺️

for multi-year calculations, just continue incrementing DOY values above 366 — it will continue working, up to maximum input of 400 satellite images. she has stamina 💀

this is an example of a temporal integration from a weather station as done by Chemin and Alexandridis (2004) 📚

🌈 References 🌈

Chemin and Alexandridis, 2004. Spatial Resolution Improvement of Seasonal Evapotranspiration for Irrigated Rice, Zhanghe Irrigation District, Hubei Province, China. Asian Journal of Geoinformatics, Vol. 5, No. 1, September 2004 (PDF)

👀 SEE ALSO 👀

i.eb.eta, i.evapo.mh, i.evapo.pt, i.evapo.pm, r.sun

the whole evapotranspiration friend group, obsessed with them 🫶

👑 AUTHOR 👑

Yann Chemin, International Rice Research Institute, The Philippines. king behavior 🌾

🔥 SOURCE CODE 🔥

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

Accessed: Saturday Jan 17 05:41:40 2026

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© 2003-2025 GRASS Development Team, GRASS GIS 8.4.2 Reference Manual

that's the whole page, bestie — every flag, every parameter, every formula, untouched. iykyk 💜

okay and one lil sign-off from me to you: this whole thing lives in GRASS GIS 8.4.2, it's page i.evapo.time(1), and the copyright sits with the © 2003-2025 GRASS Development Team. slay, bye 💖✨🎀🦋🌸

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