h.interception given the LAI [-], the ETPls [mm/h], the leaf storage level at the previous step Co [mm], the rain R [mm/h], the timestep Ts [h], and the vegetation density Vc [%] the command estimates the interception losses IL [mm], the drainage D [mm] and the canopy storage level at the end of the step Ct [mm].

This algorithm is a modification of the Rutter model in order to take into account the temporal variability of the rainfall.

For more details on the algorithms see the references.


The program will run non-interactively if the user specifies program arguments settings on the command line using the following form:
h.interception LAI=name ETPls=name Co=name R=name [Ts=name] Vc=name IL=name D=name Ct=name

Alternatively, the user can simply type h.interception on the command line and the program will ask for parameter values settings interactively, using the standard GRASS parser interface.


Input: Leaf Area Index raster map [-]. Required.
Input: Potential Evapotranspiration for a liquid surface raster map [mm/h]. Required.
Co =name
Input: initial canopy storage level raster map [mm]. Required.
R =name
Input: rainfall intensity raster map [mm/h]. Required.
Ts =name
Input: camputational time step value [h]. Optional (default 1).
Vc =name
Input: vegetatin cover raster map [%]. Required.
IL =name
Output: estimated interception losses raster map [mm]. Required.
D =name
Output: estimated drained water raster map [mm]. Required.
Ct =name
Output: estimated canopy storage level raster map [mm] at the end of the timestep. Required.


The estimated D raster map (water drained from the vegetation to the groud) is calculated for each cell on the basis of the vegetation cover fraction. In order to evaluate the total water reaching the groud, and therefore available for runoff and infiltration, this quantity should be sommed to the rain directly falling to the ground, and eventually to the water caming from the snowmelt.

The sum of these three components outputted can be calculated by means of teh r.mapcalc command.

r.mapcalc 'NETrain = D + (1-Vc)*R + snowmelt';



Original version of program: The HydroFOSS project, 2006, IST-SUPSI. (
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


[1] Cannata M., 2006. GIS embedded approach for Free & Open Source Hydrological Modelling. PhD thesis, Department of Geodesy and Geomatics, Polytechnic of Milan, Italy.

Zeng, N., JW Shuttleworth, and J. Gash, 2000. Influence of temporal variability of rainfall on interception loss. J. of Hydrology, 228 3-4, 228-241.

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