TWI: topographic wetness index

[WalidGharianiEAGLE]

Are there any plans to implement support for the Topographic Wetness Index (TWI)? For reference, TWI is available in GRASS GIS as described in their documentation: https://grass.osgeo.org/grass-stable/manuals/r.topidx.html.

[rhugonnet]

Hi @WalidGharianiEAGLE,

We don't have any ongoing work on TWI, but we'd like to support it in the long-term along with other terrain attributes especially relevant to hydrological studies.

Right now, our core dev team is mostly composed of experts in elevation data analysis for topographical change, so a bit more glaciology/geomorphology-oriented. It would be nice to complement with hydrological expertise.

If my understand is correct, TWI requires 3 components: 1/ A flow accumulation algorithm, 2/ A flow width algorithm and 3/ A slope algorithm. I think Kopecký et al. (2021) gives a good overview of different algorithms (Table 1).
We currently support 3/, but neither 1/ nor 2/. We'd be happy to help add 1/ and 2/, but it would be nice to do it in coordination with hydrologists. 😄

[rhugonnet]

Also: To derive your own TWI with existing Python tools, you could combine the flow accumulation and flow width of PySheds with our terrain slope.