SAGA Wetness Index

Author: J.Boehner, O.Conrad (c) 2001
Menu: Terrain Analysis | Hydrology | Topographic Indices

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

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. https://esdac.jrc.ec.europa.eu/ESDB_Archive/eusoils_docs/esb_rr/n07_ESBResRep07/601Bohner.pdf.
Boehner, 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`	-	-
Input	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	Grid System	grid system	`PARAMETERS_GRID_SYSTEM`	-	-
	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

Command Line

Usage: saga_cmd ta_hydrology 15 [-DEM ] [-WEIGHT ] [-AREA ] [-SLOPE ] [-AREA_MOD ] [-TWI ] [-SUCTION ] [-AREA_TYPE ] [-SLOPE_TYPE ] [-SLOPE_MIN ] [-SLOPE_OFF ] [-SLOPE_WEIGHT ]
  -DEM:            	Elevation
	grid, input
  -WEIGHT:         	Weights
	grid, input, optional
  -AREA:           	Catchment Area
	grid, output, optional
  -SLOPE:          	Catchment Slope
	grid, output, optional
  -AREA_MOD:       	Modified Catchment Area
	grid, output, optional
  -TWI:            	Topographic Wetness Index
	grid, output
  -SUCTION:     	Suction
	floating point number
	Minimum: 0.000000
	Default: 10.000000
  -AREA_TYPE:      	Type of Area
	choice
	Available Choices:
	[0] total catchment area
	[1] square root of catchment area
	[2] specific catchment area
	Default: 2
  -SLOPE_TYPE:     	Type of Slope
	choice
	Available Choices:
	[0] local slope
	[1] catchment slope
	Default: 1
  -SLOPE_MIN:   	Minimum Slope
	floating point number
	Minimum: 0.000000
	Default: 0.000000
  -SLOPE_OFF:   	Offset Slope
	floating point number
	Minimum: 0.000000
	Default: 0.100000
  -SLOPE_WEIGHT:	Slope Weighting
	floating point number
	Minimum: 0.000000
	Default: 1.000000