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

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)"

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.pm, 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

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.

       Last changed: $Date: 2015-08-01 21:15:31 +0200 (Sat, 01 Aug 2015) $

       Main index | Imagery index | Topics index | Keywords index | Full index

       © 2003-2016 GRASS Development Team, GRASS GIS 7.0.3 Reference Manual