.TH i.evapo.pm 1grass "" "GRASS 8.4.1RC1" "GRASS GIS User's Manual"
.SH NAME
\fI\fBi.evapo.pm\fR\fR  \- Computes potential evapotranspiration calculation with hourly Penman\-Monteith.
.SH KEYWORDS
imagery, evapotranspiration
.SH SYNOPSIS
\fBi.evapo.pm\fR
.br
\fBi.evapo.pm \-\-help\fR
.br
\fBi.evapo.pm\fR [\-\fBzn\fR] \fBelevation\fR=\fIname\fR \fBtemperature\fR=\fIname\fR \fBrelativehumidity\fR=\fIname\fR \fBwindspeed\fR=\fIname\fR \fBnetradiation\fR=\fIname\fR \fBcropheight\fR=\fIname\fR \fBoutput\fR=\fIname\fR  [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-z\fR" 4m
.br
Set negative evapotranspiration to zero
.IP "\fB\-n\fR" 4m
.br
Use Night\-time
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBelevation\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input elevation raster map [m a.s.l.]
.IP "\fBtemperature\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input temperature raster map [C]
.IP "\fBrelativehumidity\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input relative humidity raster map [%]
.IP "\fBwindspeed\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input wind speed raster map [m/s]
.IP "\fBnetradiation\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input net solar radiation raster map [MJ/m2/h]
.IP "\fBcropheight\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input crop height raster map [m]
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output raster map [mm/h]
.SH DESCRIPTION
.PP
\fIi.evapo.pm\fR, 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).
.PP
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.
.PP
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.
.PP
Land and water surfaces are idenfyied by Vh:
.RS 4n
.IP \(bu 4n
where Vh gt 0 vegetation is present and evapotranspiration is calculated;
.IP \(bu 4n
where Vh = 0 bare ground is present and evapotranspiration is calculated;
.IP \(bu 4n
where Vh lt 0 water surface is present and evaporation is calculated.
.RE
.PP
For more details on the algorithms see [1,2,3].
.SH NOTES
.PP
Net solar radiation map in MJ/(m2*h) can be computed from the combination of the r.sun ,
run in mode 1, and the \fIr.mapcalc\fR commands.
.PP
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 \fIi.evapo.PM\fR command.
.PP
Example:
.br
.nf
\fC
r.sun \-s elevin=dem aspin=aspect slopein=slope lin=2 albedo=alb_Mar \(rs
      incidout=out beam_rad=beam diff_rad=diffuse refl_rad=reflected \(rs
      day=73 time=13:00 dist=100;
r.mapcalc \(dqNSR = 0.0036 * (beam + diffuse + reflected)\(dq
\fR
.fi
.SH REFERENCES
.PP
[1] Cannata M., 2006.
GIS embedded approach for Free & Open Source Hydrological Modelling. PhD thesis, Department of Geodesy and Geomatics, Polytechnic of Milan, Italy.
.PP
[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
.PP
[3] Penman, H. L. 1948. Natural evaporation from open water,
bare soil and grass. Proc. Roy. Soc. London, A193, pp. 120\-146.
.SH SEE ALSO
The HydroFOSS
project at IST\-SUPSI (Institute of Earth Sciences \- University school of
applied science for the Southern Switzerland)
.br
\fI
i.evapo.mh,
i.evapo.time,
r.sun,
r.mapcalc
\fR
.SH AUTHORS
.PP
Original version of program: The HydroFOSS project, 2006, IST\-SUPSI. (http://istgis.ist.supsi.ch:8001/geomatica/index.php?id=1)
\fIMassimiliano Cannata, Scuola Universitaria Professionale della Svizzera Italiana \- Istituto Scienze della Terra\fR
.br
\fIMaria A. Brovelli, Politecnico di Milano \- Polo regionale di Como\fR
.PP
Contact: Massimiliano Cannata
.SH SOURCE CODE
.PP
Available at:
i.evapo.pm source code
(history)
.PP
Accessed: Wednesday Feb 12 05:32:22 2025
.PP
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.PP
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GRASS Development Team,
GRASS GIS 8.4.1RC1 Reference Manual
