NAME

       r.topidx  - Creates a topographic index (wetness index) raster map from an elevation raster map.

KEYWORDS

       raster, hydrology, wetness, topographic index

SYNOPSIS

       r.topidx
       r.topidx --help
       r.topidx input=name output=name  [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       input=name [required]
           Name of input elevation raster map

       output=name [required]
           Name for output topographic index raster map

DESCRIPTION

       r.topidx creates topographic index (wetness index), ln(a/tan(beta)), map from elevation map

       where
       a: the area of the hillslope per unit contour length that drains through any point,

       tan(beta): the local surface topographic slope (delta vertical) / (delta horizontal).

       Input  maps  may  have  NULL  values.   For  example,  if you have a MASK for a watershed (basin map from
       r.water.outlet), the following command will create a masked elevation map (belev):
       r.mapcalc "belev = if(isnull(basin), basin, elev)"

       r.stats -Anc prints out averaged statistics for topographic index.

EXAMPLE

       Running the command below will generate the topographic index map shown in the figure:
       g.region raster=elevation -p
       r.topidx input=elevation output=topidx_elevation
       Figure: topographic index map derived from elevation map

SEE ALSO

        r.topmodel, r.water.outlet, r.mapcalc
       Known issues

REFERENCES

       Cho, H., 2000. GIS Hydrological Modeling System by Using Programming Interface of GRASS. Master’s Thesis,
       Department of Civil Engineering, Kyungpook National University, Korea.

       Moore,  I.D.,  R.B.  Grayson,  and A.R. Ladson, 1991. Digital Terrain Modeling: A Review of Hydrological,
       Geomorphological, and Biological Applications.  Hydrological Processes 5:3-30.

AUTHORS

       Huidae Cho
       Hydro Laboratory, Kyungpook National University, South Korea

       Based on GRIDATB.FOR by Keith Beven.

SOURCE CODE

       Available at: r.topidx source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual