i.evapo.pm
Computes potential evapotranspiration calculation with hourly Penman-Monteith.
i.evapo.pm [-zn] elevation=name temperature=name relativehumidity=name windspeed=name netradiation=name cropheight=name output=name [--overwrite] [--verbose] [--quiet] [--qq] [--ui]
Example:
i.evapo.pm elevation=name temperature=name relativehumidity=name windspeed=name netradiation=name cropheight=name output=name
grass.script.run_command("i.evapo.pm", elevation, temperature, relativehumidity, windspeed, netradiation, cropheight, output, flags=None, overwrite=False, verbose=False, quiet=False, superquiet=False)
Example:
gs.run_command("i.evapo.pm", elevation="name", temperature="name", relativehumidity="name", windspeed="name", netradiation="name", cropheight="name", output="name")
Parameters
elevation=name [required]
Name of input elevation raster map [m a.s.l.]
temperature=name [required]
Name of input temperature raster map [C]
relativehumidity=name [required]
Name of input relative humidity raster map [%]
windspeed=name [required]
Name of input wind speed raster map [m/s]
netradiation=name [required]
Name of input net solar radiation raster map [MJ/m2/h]
cropheight=name [required]
Name of input crop height raster map [m]
output=name [required]
Name for output raster map [mm/h]
-z
Set negative evapotranspiration to zero
-n
Use Night-time
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--qq
Very quiet module output
--ui
Force launching GUI dialog
elevation : str, required
Name of input elevation raster map [m a.s.l.]
Used as: input, raster, name
temperature : str, required
Name of input temperature raster map [C]
Used as: input, raster, name
relativehumidity : str, required
Name of input relative humidity raster map [%]
Used as: input, raster, name
windspeed : str, required
Name of input wind speed raster map [m/s]
Used as: input, raster, name
netradiation : str, required
Name of input net solar radiation raster map [MJ/m2/h]
Used as: input, raster, name
cropheight : str, required
Name of input crop height raster map [m]
Used as: input, raster, name
output : str, required
Name for output raster map [mm/h]
Used as: output, raster, name
flags : str, optional
Allowed values: z, n
z
Set negative evapotranspiration to zero
n
Use Night-time
overwrite: bool, optional
Allow output files to overwrite existing files
Default: False
verbose: bool, optional
Verbose module output
Default: False
quiet: bool, optional
Quiet module output
Default: False
superquiet: bool, optional
Very quiet module output
Default: False
DESCRIPTION
i.evapo.pm, given the vegetation height (hc), humidity (RU), wind speed at two meters height (WS), temperature (T), digital terrain model (DEM), and net radiation (NSR) raster input maps, calculates the potential evapotranspiration map (EPo).
Optionally the user can activate a flag (-z) that allows him setting to zero all of the negative evapotranspiration cells; in fact these negative values motivated by the condensation of the air water vapour content, are sometime undesired because they can produce computational problems. The usage of the flag -n detect that the module is run in night hours and the appropriate soil heat flux is calculated.
The algorithm implements well known approaches: the hourly Penman-Monteith method as presented in Allen et al. (1998) for land surfaces and the Penman method (Penman, 1948) for water surfaces.
Land and water surfaces are idenfyied by Vh:
- where Vh gt 0 vegetation is present and evapotranspiration is calculated;
- where Vh = 0 bare ground is present and evapotranspiration is calculated;
- where Vh lt 0 water surface is present and evaporation is calculated.
For more details on the algorithms see [1,2,3].
NOTES
Net solar radiation map in MJ/(m2*h) can be computed from the combination of the r.sun , run in mode 1, and the r.mapcalc commands.
The sum of the three radiation components outputted by r.sun (beam, diffuse, and reflected) multiplied by the Wh to Mj conversion factor (0.0036) and optionally by a clear sky factor [0-1] allows the generation of a map to be used as an NSR input for the i.evapo.PM command.
Example:
r.sun -s elevin=dem aspin=aspect slopein=slope lin=2 albedo=alb_Mar \
incidout=out beam_rad=beam diff_rad=diffuse refl_rad=reflected \
day=73 time=13:00 dist=100;
r.mapcalc "NSR = 0.0036 * (beam + diffuse + reflected)"
REFERENCES
[1] Cannata M., 2006. GIS embedded approach for Free & Open Source Hydrological Modelling. PhD thesis, Department of Geodesy and Geomatics, Polytechnic of Milan, Italy.
[2] Allen, R.G., L.S. Pereira, D. Raes, and M. Smith. 1998. Crop Evapotranspiration: Guidelines for computing crop water requirements. Irrigation and Drainage Paper 56, Food and Agriculture Organization of the United Nations, Rome, pp. 300
[3] Penman, H. L. 1948. Natural evaporation from open water, bare soil and grass. Proc. Roy. Soc. London, A193, pp. 120-146.
SEE ALSO
The HydroFOSS project at
IST-SUPSI (Institute of Earth Sciences - University school of applied
science for the Southern Switzerland)
i.evapo.mh, i.evapo.time,
r.sun, r.mapcalc
AUTHORS
Original version of program: The
HydroFOSS
project, 2006, IST-SUPSI.
(http://istgis.ist.supsi.ch:8001/geomatica/index.php?id=1) Massimiliano
Cannata, Scuola Universitaria Professionale della Svizzera Italiana -
Istituto Scienze della Terra
Maria A. Brovelli, Politecnico di Milano - Polo regionale di Como
Contact: Massimiliano Cannata
SOURCE CODE
Available at: i.evapo.pm source code
(history)
Latest change: Friday Feb 07 19:16:09 2025 in commit a82a39f