Tool Name	SAGA Wetness Index
Tool ID	15
Library ID	ta_hydrology
Version	1.0
Author(s)	J.Böhner, O.Conrad (c) 2001

Description

The 'SAGA Wetness Index' is, as the name says, similar to the 'Topographic Wetness Index' (TWI), but it is based on a modified catchment area calculation ('Modified Catchment Area'), which does not think of the flow as very thin film. As result it predicts for cells situated in valley floors with a small vertical distance to a channel a more realistic, higher potential soil moisture compared to the standard TWI calculation.

References

Böhner, J., Köthe, 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. https://esdac.jrc.ec.europa.eu/ESDB_Archive/eusoils_docs/esb_rr/n07_ESBResRep07/601Bohner.pdf

Böhner, J., Selige, T. (2006): Spatial prediction of soil attributes using terrain analysis and climate regionalisation. In: Boehner, J., McCloy, K.R., Strobl, J. [Eds.]: SAGA - Analysis and Modelling Applications, Goettinger Geographische Abhandlungen, Goettingen: 13-28. https://downloads.sourceforge.net/saga-gis/gga115_02.pdf

Parameters

Name	Type	Identifier	Description	Constraints
Input
Elevation	grid, input	DEM
Weights	grid, input, optional	WEIGHT
Output
Catchment Area	grid, output, optional	AREA
Catchment Slope	grid, output, optional	SLOPE
Modified Catchment Area	grid, output, optional	AREA_MOD
Topographic Wetness Index	grid, output	TWI
Options
Suction	floating point number	SUCTION	the lower this value is the stronger is the suction effect	Minimum: 0.000000 Default: 10.000000
Type of Area	choice	AREA_TYPE		Available Choices: [0] total catchment area [1] square root of catchment area [2] specific catchment area Default: 2
Type of Slope	choice	SLOPE_TYPE		Available Choices: [0] local slope [1] catchment slope Default: 1
Minimum Slope	floating point number	SLOPE_MIN		Minimum: 0.000000 Default: 0.000000
Offset Slope	floating point number	SLOPE_OFF		Minimum: 0.000000 Default: 0.100000
Slope Weighting	floating point number	SLOPE_WEIGHT	weighting factor for slope in index calculation	Minimum: 0.000000 Default: 1.000000