Slope Units Delineation


The software r.slopeunits requires a DEM, an optional raster layer showing alluvial plains, and the following user-defined parameters :

  • the initial flow accumulation area threshold (t in square meters),

  • the reduction factor r (integer, >1), that is used to calculate, iteratively, new values for the flow accumulation area threshold (t = t-t/r). Values larger than 5 are recommended.

  • the minimum surface area for the slope-units (a in square meters),

  • the minimum circular variance of terrain aspect within a slope-units (c, varies between 0 and 1, where 0 means no variance, i.e. cells dip in the same direction, and 1 means maximum variance)

  • the maximum surface area for the slope-units (maxarea, in square meters, optional),

  • threshold area value for the cleaning procedures (cleansize, in square meters, used to remove very small slope units that may occur give some geomorphological conditions)





Download slope units map for the 20 administrative regions of Italy:

  1. Abruzzo
  2. Basilicata
  3. Calabria
  4. Campania
  5. Emilia-Romagna
  6. Friuli-Venezia Giulia
  7. Lazio
  8. Liguria
  9. Lombardia
  10. Marche
  11. Molise
  12. Piemonte
  13. Puglia
  14. Sardegna
  15. Sicilia
  16. Trentino-Alto Adige
  17. Toscana
  18. Umbria
  19. Valle D'Aosta
  20. Veneto 



GRASS GIS 7.0, Python, Bash


Installation and run

The software have been tested on a Ubuntu 14.04 LTS server but should run on a generic GNU/Linux machine.

The two files provided must be copied inside the “scripts” folder of the GRASS GIS installation directory. The must be set executable. A typical approach, for the installation, is:

#open a bash shell

#move to the download folder, e.g.

cd /home/$USER/Downloads


#move the files

mv r.slopeunits /usr/lib/grass70/scripts

mv /usr/lib/grass70/scripts


#give execution rights

chmod ugo+x /usr/lib/grass70/scripts/r.slopeunits

chmod ugo+x /usr/lib/grass70/scripts/


#Run GRASS GIS, move in the location containing the digital elevation model type and:

r.slopeunits --help

#to see the options. The minimal command line to obtain a slope-units delineation is

r.slopeunits demmap=[dem] slumap=[output_SU_map] thresh=[t, square meters] circularvariance=[c] areamin=[a, square meters] reductionfactor=[r, r>2] maxiteration=[max number of iterations]

#see M. Alvioli, I. Marchesini, P. Reichenbach, M. Rossi, F. Fiorucci, F. Ardizzone, F. Guzzetti

#(2015) for explanations and additional options.


#please address comments, questions and gux fixes rquests to: ivan.marchesini[AT];





  • Alvioli M., Marchesini I., Reichenbach P., Rossi M., Ardizzone F., Fiorucci F., Guzzetti F. (2016).
    Automatic delineation of geomorphological slope units with r.slopeunits v1.0 and their optimization for landslide susceptibility modeling.
    Geoscientific Model Development 9, 3975-3991.

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last modified 2020-03-09T12:56:45+02:00