i.eb.h_sebal95 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 sensible heat flux map (h0).
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 less than 0 vegetation is present and evapotranspiration is calculated;
- where Vh=0 bare ground is present and evapotranspiration is calculated;
- where Vh more than 0 water surface is present and evaporation is calculated;
For more details on the algorithms see [1].
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.
[1] Bastiaanssen, W.G.M., 1995.
Estimation of Land surface paramters by remote sensing under clear-sky conditions. PhD thesis, Wageningen University, Wageningen, The Netherlands.
[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.
Contact: Yann Chemin
Available at:
i.eb.hsebal95 source code
(history)
Latest change: Monday Jan 30 19:52:26 2023 in commit: cac8d9d848299297977d1315b7e90cc3f7698730
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© 2003-2024
GRASS Development Team,
GRASS GIS 8.4.1dev Reference Manual
example:
r.sun elev_in=dem asp_in=aspect slope_in=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
i.eb.h_iter,
i.eb.h0,
i.evapo.pm
REFERENCES
AUTHOR
Yann Chemin
International Rice Research Institute, Los Banos, The Philippines.
International Water management Institute, Colombo, Sri Lanka.
SOURCE CODE