RSAGA (version 1.4.0)

rsaga.wetness.index: SAGA Modules SAGA Wetness Index

Description

Calculate the SAGA Wetness Index (SWI), a modified topographic wetness index (TWI)

Usage

rsaga.wetness.index(
  in.dem,
  out.wetness.index,
  out.carea,
  out.cslope,
  out.mod.carea,
  suction,
  area.type,
  slope.type,
  slope.min,
  slope.offset,
  slope.weight,
  t.param,
  env = rsaga.env(),
  ...
)

Value

The type of object returned depends on the intern argument passed to the rsaga.geoprocessor(). For intern=FALSE it is a numerical error code (0: success), or otherwise (the default) a character vector with the module's console output.

Arguments

in.dem

input: digital elevation model (DEM) as SAGA grid file (default file extension: .sgrd)

out.wetness.index

output file (optional): wetness index grid file name. Existing files of the same name will be overwritten!

out.carea

output file (optional): catchment area grid file name

out.cslope

output file (optional): catchment slope grid file name

out.mod.carea

output file (optional): file name of modified catchment area grid

suction

SAGA GIS 2.1.0+: positive numeric value (optional): the lower this value is the stronger is the suction effect; defaults to a value of 10 (more detailed information is currently not available in the SAGA GIS documentation

area.type

character or numeric (optional): type of area: "absolute" (or numeric code 0): absolute catchment area; "square root" (code 1; the default e.g. in SAGA 2.3.1): square root of catchment area; "specific" (code 2; the default e.g. in SAGA 8.4.1): specific catchment area

slope.type

character or numeric (optional): type of slope: "local" (or numeric code 0): local slope; "catchment" (or code 1; the default): catchment slope.

slope.min

numeric (optional): minimum slope; default: 0

slope.offset

numeric (optional): offset slope; default: 0.1

slope.weight

numeric (optional): weighting factor for slope in index calculation; default: 1

t.param

SAGA GIS up to version 2.0.8: positive numeric value (optional): undocumented

env

A SAGA geoprocessing environment, see rsaga.env().)

...

optional arguments to be passed to rsaga.geoprocessor()

Author

Alexander Brenning (R interface), Juergen Boehner and Olaf Conrad (SAGA module)

Details

The SAGA Wetness Index is similar to the Topographic Wetness Index (TWI), but it is based on a modified catchment area calculation (out.mod.carea), which does not treat the flow as a thin film as done in the calculation of catchment areas in conventional algorithms. As a result, the SWI tends to assign a more realistic, higher potential soil wetness than the TWI to grid cells situated in valley floors with a small vertical distance to a channel.

This module and its arguments changed substantially from SAGA GIS 2.0.8 to version 2.1.0. It appears to me that the new algorithm is similar (but not identical) to the old one when using area.type="absolute" and slope.type="local" but I haven't tried out all possible options. This help file will be updated as soon as additional documentation becomes available.

References

Boehner, J., Koethe, R. Conrad, O., Gross, J., Ringeler, A., Selige, T. (2002): Soil Regionalisation by Means of Terrain Analysis and Process Parameterisation. In: Micheli, E., Nachtergaele, F., Montanarella, L. (ed.): Soil Classification 2001. European Soil Bureau, Research Report No. 7, EUR 20398 EN, Luxembourg. pp.213-222.

Boehner, J. and Selige, T. (2006): Spatial prediction of soil attributes using terrain analysis and climate regionalisation. In: Boehner, J., McCloy, K.R., Strobl, J. [Ed.: SAGA - Analysis and Modelling Applications, Goettinger Geographische Abhandlungen, Goettingen: 13-28.

See Also

rsaga.parallel.processing(), rsaga.geoprocessor(), rsaga.env()

Examples

if (FALSE) {
# using SAGA grids:
rsaga.wetness.index("dem.sgrd","swi.sgrd")
}