r.topidx - GRASS GIS manual

Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

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
EXAMPLE
SEE ALSO
REFERENCES
AUTHORS

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

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)

Latest change: Monday Nov 18 20:15:32 2019 in commit: 1a1d107e4f6e1b846f9841c2c6fabf015c5f720d