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Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.


i.evapo.time - Computes temporal integration of satellite ET actual (ETa) following the daily ET reference (ETo) from meteorological station(s).


imagery, evapotranspiration


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]


Allow output files to overwrite existing files
Print usage summary
Verbose module output
Quiet module output
Force launching GUI dialog


eta=name[,name,...] [required]
Names of satellite ETa raster maps [mm/d or cm/d]
eta_doy=name[,name,...] [required]
Names of satellite ETa Day of Year (DOY) raster maps [0-400] [-]
eto=name[,name,...] [required]
Names of meteorological station ETo raster maps [0-400] [mm/d or cm/d]
eto_doy_min=float [required]
Value of DOY for ETo first day
start_period=float [required]
Value of DOY for the first day of the period studied
end_period=float [required]
Value of DOY for the last day of the period studied
output=name [required]
Name for output raster map

Table of contents


i.evapo.time (i.evapo.time_integration) integrates ETa in time following a reference ET (typically) from a set of meteorological stations dataset. Inputs: Method:
  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


ETo images preparation: If you only have one meteorological station data set, the easiest way is:
for ETo_val in Eto[1] Eto[2] ...
	r.mapcalc "eto$n = $ETo_val" 
	`expr n = n + 1`
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.

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.

For multi-year calculations, just continue incrementing DOY values above 366, it will continue working, up to maximum input of 400 satellite images.


i.eb.eta,,,, r.sun


Yann Chemin, International Rice Research Institute, The Philippines


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

Latest change: Wednesday Feb 09 22:41:37 2022 in commit: c37871b51d202b155b64ba04288c4242826936f2

Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

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