SAGA-GIS Tool Library Documentation (v9.1.2)

Tool SAGA Wetness Index

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


Parameters

 NameTypeIdentifierDescriptionConstraints
InputElevationGrid, inputDEM--
Weights (*)Grid, input, optionalWEIGHT--
OutputCatchment Area (*)Grid, output, optionalAREA--
Catchment Slope (*)Grid, output, optionalSLOPE--
Modified Catchment Area (*)Grid, output, optionalAREA_MOD--
Topographic Wetness IndexGrid, outputTWI--
OptionsGrid SystemGrid systemPARAMETERS_GRID_SYSTEM--
SuctionFloating pointSUCTIONthe lower this value is the stronger is the suction effectMinimum: 0.000000
Default: 10.000000
Type of AreaChoiceAREA_TYPE-Available Choices:
[0] total catchment area
[1] square root of catchment area
[2] specific catchment area
Default: 2
Type of SlopeChoiceSLOPE_TYPE-Available Choices:
[0] local slope
[1] catchment slope
Default: 1
Minimum SlopeFloating pointSLOPE_MIN-Minimum: 0.000000
Default: 0.000000
Offset SlopeFloating pointSLOPE_OFF-Minimum: 0.000000
Default: 0.100000
Slope WeightingFloating pointSLOPE_WEIGHTweighting factor for slope in index calculationMinimum: 0.000000
Default: 1.000000
(*) optional

Command-line

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