1i.evapo.pm(1)               GRASS GIS User's Manual              i.evapo.pm(1)
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NAME

6       i.evapo.pm   -  Computes  potential evapotranspiration calculation with
7       hourly Penman-Monteith.
8

KEYWORDS

10       imagery, evapotranspiration
11

SYNOPSIS

13       i.evapo.pm
14       i.evapo.pm --help
15       i.evapo.pm [-zn] elevation=name temperature=name  relativehumidity=name
16       windspeed=name  netradiation=name cropheight=name output=name  [--over‐
17       write]  [--help]  [--verbose]  [--quiet]  [--ui]
18
19   Flags:
20       -z
21           Set negative evapotranspiration to zero
22
23       -n
24           Use Night-time
25
26       --overwrite
27           Allow output files to overwrite existing files
28
29       --help
30           Print usage summary
31
32       --verbose
33           Verbose module output
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35       --quiet
36           Quiet module output
37
38       --ui
39           Force launching GUI dialog
40
41   Parameters:
42       elevation=name [required]
43           Name of input elevation raster map [m a.s.l.]
44
45       temperature=name [required]
46           Name of input temperature raster map [C]
47
48       relativehumidity=name [required]
49           Name of input relative humidity raster map [%]
50
51       windspeed=name [required]
52           Name of input wind speed raster map [m/s]
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54       netradiation=name [required]
55           Name of input net solar radiation raster map [MJ/m2/h]
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57       cropheight=name [required]
58           Name of input crop height raster map [m]
59
60       output=name [required]
61           Name for output raster map
62

DESCRIPTION

64       i.evapo.pm, given the vegetation height (hc), humidity (RU), wind speed
65       at  two  meters  height  (WS),  temperature  (T), digital terrain model
66       (DEM), and net radiation (NSR) raster input maps, calculates the poten‐
67       tial evapotranspiration map (EPo).
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69       Optionally the user can activate a flag (-z) that allows him setting to
70       zero all of the negative evapotranspiration cells; in fact these  nega‐
71       tive  values motivated by the condensation of the air water vapour con‐
72       tent, are sometime undesired because they  can  produce   computational
73       problems.  The  usage  of  the flag -n detect that the module is run in
74       night hours and the appropriate soil heat flux is calculated.
75
76       The algorithm implements well known approaches: the hourly  Penman-Mon‐
77       teith  method as presented in Allen et al. (1998) for land surfaces and
78       the Penman method (Penman, 1948) for water surfaces.
79
80       Land and water surfaces are idenfyied by Vh:
81
82           ·   where Vh gt 0 vegetation is present and  evapotranspiration  is
83               calculated;
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85           ·   where  Vh  = 0 bare ground is present and evapotranspiration is
86               calculated;
87
88           ·   where Vh lt 0 water surface is present and evaporation is  cal‐
89               culated.
90
91       For more details on the algorithms see [1,2,3].
92

NOTES

94       Net  solar radiation map in MJ/(m2*h) can be computed from the combina‐
95       tion of the r.sun , run in mode 1, and the r.mapcalc commands.
96
97       The sum of the three radiation components  outputted  by  r.sun  (beam,
98       diffuse,  and  reflected)  multiplied by the Wh to Mj conversion factor
99       (0.0036) and optionally by a clear sky factor [0-1] allows the  genera‐
100       tion of a map to be used as an NSR input for the i.evapo.PM command.
101
102       Example:
103       r.sun -s elevin=dem aspin=aspect slopein=slope lin=2 albedo=alb_Mar \
104             incidout=out beam_rad=beam diff_rad=diffuse refl_rad=reflected \
105             day=73 time=13:00 dist=100;
106       r.mapcalc "NSR = 0.0036 * (beam + diffuse + reflected)"
107

SEE ALSO

109       The  HydroFOSS project at IST-SUPSI (Institute of Earth Sciences - Uni‐
110       versity school of applied science for the Southern Switzerland)
111        i.evapo.mh, i.evapo.time, r.sun, r.mapcalc
112

AUTHORS

114       Original version of program: The HydroFOSS  project,  2006,  IST-SUPSI.
115       (http://istgis.ist.supsi.ch:8001/geomatica/index.php?id=1)
116       Massimiliano Cannata, Scuola Universitaria Professionale della Svizzera
117       Italiana - Istituto Scienze della Terra
118       Maria A. Brovelli, Politecnico di Milano - Polo regionale di Como
119
120       Contact: Massimiliano Cannata
121

REFERENCES

123       [1] Cannata M., 2006.  GIS embedded approach for  Free  &  Open  Source
124       Hydrological  Modelling.  PhD thesis, Department of Geodesy and Geomat‐
125       ics, Polytechnic of Milan, Italy.
126
127       [2] Allen, R.G., L.S. Pereira, D. Raes, and M. Smith. 1998.  Crop Evap‐
128       otranspiration:  Guidelines  for  computing  crop  water  requirements.
129       Irrigation and Drainage Paper 56, Food and Agriculture Organization  of
130       the United Nations, Rome, pp. 300
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132       [3]  Penman, H. L. 1948. Natural evaporation from open water, bare soil
133       and grass. Proc. Roy. Soc. London, A193, pp. 120-146.
134

SOURCE CODE

136       Available at: i.evapo.pm source code (history)
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138       Main index | Imagery index | Topics index | Keywords index |  Graphical
139       index | Full index
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141       © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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145GRASS 7.8.5                                                      i.evapo.pm(1)
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