1i.evapo.pm(1) Grass User's Manual i.evapo.pm(1)
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6 i.evapo.pm - Computes potential evapotranspiration calculation with
7 hourly Penman-Monteith.
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10 imagery, evapotranspiration
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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]
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19 Flags:
20 -z
21 Set negative evapotranspiration to zero
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23 -n
24 Use Night-time
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26 --overwrite
27 Allow output files to overwrite existing files
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29 --help
30 Print usage summary
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32 --verbose
33 Verbose module output
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35 --quiet
36 Quiet module output
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38 --ui
39 Force launching GUI dialog
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41 Parameters:
42 elevation=name [required]
43 Name of input elevation raster map [m a.s.l.]
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45 temperature=name [required]
46 Name of input temperature raster map [C]
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48 relativehumidity=name [required]
49 Name of input relative humidity raster map [%]
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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]
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60 output=name [required]
61 Name for output raster map
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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.
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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.
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80 Land and water surfaces are idenfyied by Vh:
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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;
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88 · where Vh lt 0 water surface is present and evaporation is cal‐
89 culated.
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91 For more details on the algorithms see [1,2,3].
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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.
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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.
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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)"
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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
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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
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120 Contact: Massimiliano Cannata
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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.
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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.
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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 © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
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145GRASS 7.8.2 i.evapo.pm(1)