1

In which units do I have to calculate Slope to use as an input for the LS Factor tool in SAGA (degrees, %, radians)?

I couldn't find anything in the documentation.

2

Use Slope in radians as input raster.

Some hints are in the code, for instance:

Line 567: if( Slope < 0.08975817419 )       // < 9% Steigung := atan(0.09), ca. 5 Degree

To be more precise, please also check out any one of the reference paper. For instance:

Moore, I.D., Grayson, R.B., Ladson, A.R. (1991): Digital terrain modelling: a review of hydrogical, geomorphological, and biological applications. Hydrological Processes, Vol.5, No.1

The unit is understood when you see the Equation.(8)

And you can confirm how it is implemented in the LS calculation:

Line 536: LS    = (0.4 + 1) * pow(Area / 22.13, 0.4) * pow(sin(Slope) / 0.0896, 1.3)

where Slope is beta in the above.

You may already know SAGA's default output unit of the Slope is radians. (It is less intuitive if you are using the tool through QGIS, which default unit is degrees.)

  • Thank you. I usually use SAGA tools through QGIS. – Ale Feb 27 at 13:16
  • 1
    Thanks @Ale ; Sorry if this is an unsought advice - Please be careful about the Catchment Area. The input is specific catchment area which is an output from Flow width and Specific Catchment Area tool. – Kazuhito Feb 27 at 13:33
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    @Ale I now feel the note in the code (as referred above) is misleading. It says 9% but it should have been 0.09 (radians). – Kazuhito Feb 27 at 13:52
  • Thanks @Kazuhito, I though I had to use Flow accumulation tool. Great advice! – Ale Feb 27 at 19:18

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