i.eb.h_sebal95 computes the sensible heat flux [W/m2] after Bastiaanssen, 1995 in [1].

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].


Input elevation raster [m a.s.l.]. Required.
Input temperature raster [°C]. Required.
RH =name
Input relative humidity raster [%]. Required.
WS =name
Input wind speed at two meters raster [m/s]. Required.
NSR =name
Input net solar radiation raster [MJ/(m2*h)]. Required.
Vh =name
Input vegetation heigth raster [m]. Required.
ETP =name
Output evapotranspiration raster [mm/h]. Required.


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 command.
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)';



[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.


Yann Chemin
International Rice Research Institute, Los Banos, The Philippines.
International Water management Institute, Colombo, Sri Lanka.

Contact: Yann Chemin

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