i.evapo.senay - GRASS GIS manual

NAME

i.evapo.senay - Actual evapotranspiration, method after Senay (2007)

KEYWORDS

SYNOPSIS

i.evapo.senay

i.evapo.senay --help

i.evapo.senay [-edb] temperature=name albedo=name elevation=name [latitude=name] [dayofyear=name] [transmissivitysingleway=name] [waterdensity=float] [slope=name] [aspect=name] [atmosphericemissivity=float] [airtemperature=name] [surfaceemissivity=name] ndvi=name [diurnaletpotential=name] output=name [evapfr=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-e: ET Potential Map as input (By-Pass creation of one)
-d: Slope/Aspect correction
-b: Net Radiation Bandara (1998), generic Longwave calculation, need apparent atmospheric emissivity, Air temperature and surface emissivity inputs
--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:

temperature=name [required]: Name of the temperature layer [Degree Kelvin]
albedo=name [required]: Name of the Albedo layer [0.0-1.0]
elevation=name [required]: Name of the elevation layer [m]
latitude=name: Name of the degree latitude layer [dd.ddd]
dayofyear=name: Name of the Day of Year layer [0.0-366.0]
transmissivitysingleway=name: Name of the single-way transmissivity layer [0.0-1.0]
waterdensity=float: Value of the density of fresh water ~[1000-1020]; Default: 1005.0
slope=name: Name of the Slope layer ~[0-90]
aspect=name: Name of the Aspect layer ~[0-360]
atmosphericemissivity=float: Value of the apparent atmospheric emissivity (Bandara, 1998 used 0.845 for Sri Lanka)
airtemperature=name: Name of the Air Temperature layer [Kelvin], use with -b
surfaceemissivity=name: Name of the Surface Emissivity layer [-], use with -b
ndvi=name [required]: Name of the NDVI layer [-]
diurnaletpotential=name: Name of the ET Potential layer [mm/day]
output=name [required]: Name of the output Actual ET layer
evapfr=name: Name of the output evaporative fraction layer

DESCRIPTION
NOTES
TODO
SEE ALSO
REFERENCES
AUTHOR

DESCRIPTION

i.evapo.senay Calculates the diurnal actual evapotranspiration after Senay (2007). This is converting all Net radiation from the diurnal period into ET, then uses Senay equation for evaporative fraction.

It takes input maps of Albedo, surface skin temperature, latitude, day of year, single-way transmissivity and takes input value of the density of fresh water.

DEM is used for calculating min and max temperature for Senay equation.

The "-s" flag permits output map of evaporative fraction from Senay.

NOTES

If you are trying to map irrigated crops, and you know there is at least one crop pixel that is evapotranspiring at maximum (ETa=ETpot), then read this.

i.evapo.senay is highly dependent on the wet pixel being the lowest temperature in the crop pixels to work for non water stressed crops, force it that way, even if it breaks non crop areas. I suggest you reduce your region to the irrigation system boundaries, checking that it includes a bit of dry area for the hot/dry pixel.

Since it is a direct relationship to LST, evaporative fraction can be very sensitive to the kind of pixel sample you feed it with.

TODO

REFERENCES

Senay 2007

Chemin, Y., 2012. A Distributed Benchmarking Framework for Actual ET Models, in: Irmak, A. (Ed.), Evapotranspiration - Remote Sensing and Modeling. InTech. (PDF)

AUTHOR

Yann Chemin, International Rice Research Institute, The Philippines.

SOURCE CODE

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