Module 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
- 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. (pdf)
- Author: (c) 2001 by J.Boehner, O.Conrad
- Menu: Terrain Analysis|Hydrology|Topographic Indices
Parameters
| Name | Type | Identifier | Description | Constraints | |
|---|---|---|---|---|---|
| Input | Elevation | Grid (input) | DEM | - | - |
| Weights (*) | Grid (optional input) | WEIGHT | - | - | |
| Output | Catchment area | Grid (output) | AREA | - | - |
| Catchment slope | Grid (output) | SLOPE | - | - | |
| Modified Catchment Area | Grid (output) | AREA_MOD | - | - | |
| Topographic Wetness Index | Grid (output) | TWI | - | - | |
| Options | Grid system | Grid system | PARAMETERS_GRID_SYSTEM | Grid system | - |
| Suction | Floating point | 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] absolute catchment area [1] square root of catchment area [2] specific catchment area Default: 1 | |
| Type of Slope | Choice | SLOPE_TYPE | - | Available Choices: [0] local slope [1] catchment slope Default: 1 | |
| Minimum Slope | Floating point | SLOPE_MIN | - | Minimum: 0.000000 Default: 0.000000 | |
| Offset Slope | Floating point | SLOPE_OFF | - | Minimum: 0.000000 Default: 0.100000 | |
| Slope Weighting | Floating point | SLOPE_WEIGHT | weighting factor for slope in index calculation | Minimum: 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 (optional input) -AREA:<str> Catchment area Grid (output) -SLOPE:<str> Catchment slope Grid (output) -AREA_MOD:<str> Modified Catchment Area Grid (output) -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] absolute catchment area [1] square root of catchment area [2] specific catchment area Default: 1 -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