NAME

       i.evapo.pm  - Computes potential evapotranspiration calculation with hourly Penman-Monteith.

KEYWORDS

       imagery, evapotranspiration

SYNOPSIS

       i.evapo.pm
       i.evapo.pm --help
       i.evapo.pm  [-zn]  elevation=name temperature=name relativehumidity=name windspeed=name netradiation=name
       cropheight=name output=name  [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -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

       --ui
           Force launching GUI dialog

   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]

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)

       Accessed: Monday Apr 01 03:09:08 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.3.2 Reference Manual

GRASS 8.3.2                                                                                   i.evapo.pm(1grass)