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
- 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.
- Author: J.Boehner, O.Conrad (c) 2001
- Menu: Terrain Analysis|Hydrology|Topographic Indices
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 | Grid System | Grid system | PARAMETERS_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] 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 | 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, 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