Network Index¶
Computes a SCIMAP hydrological connectivity index from a DEM alone, using uniform rainfall so the result reflects terrain only — no land cover or actual rainfall pattern involved. Useful on its own to inspect terrain-driven connectivity, and as a pre-computed Connectivity input to SCIMAP Flood.
Where to find it: Processing Toolbox → SCIMAP → Network Index; toolbar
icon ("Run SCIMAP Network Index"); &SCIMAP menu.
Screenshot:
The Processing dialog with the connectivity algorithm and Wetness-Connectivity Curve outputs visible.
Parameters¶
| Parameter | Description | Default |
|---|---|---|
| Digital Elevation Model (DEM) | The DEM to route flow over. | — |
| Stream Initiation Threshold (m²) | Upslope area at which a channel starts. | 800,000 |
| Connectivity algorithm | Network Index (flow-path trace) or Percentage Downslope Saturated Length (PDSL). | Flow-path trace |
| Colour ramp | Applied to the output. | SCIMAP default |
| WhiteboxTools executable | Advanced; override the auto-detected binary. | Auto-detected |
Outputs¶
| Output | Description |
|---|---|
| Network Index | The connectivity raster. |
| Wetness-Connectivity Curve (PNG) (optional) | A scatter plot of each cell's topographic wetness index against its connectivity score. |
| Wetness-Connectivity Curve dataset (CSV) (optional) | The data behind that plot. |
Notes¶
- Because rainfall is held uniform, this isolates the terrain contribution to connectivity — useful for comparing catchments, or as a stable input that doesn't need to be recomputed for every rainfall scenario in SCIMAP Flood.
- The Wetness-Connectivity Curve outputs need matplotlib to be available in the QGIS Python environment; if it isn't, the raster is still produced and a warning explains why the plot/CSV were skipped.
Screenshot:
An example Wetness-Connectivity Curve PNG output.
Next: SCIMAP Flood.