Slope Units Delineation


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Details: 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).






Data (ready-to-use maps)


Italy: regional maps

Abruzzo Friuli-Venezia Giulia Molise Trentino-Alto Adige
Basilicata Lazio Piemonte Toscana
Calabria Liguria Puglia Umbria
Campania Lombardia Sardegna Valle D'Aosta
Emilia-Romagna Marche Sicilia Veneto


Italy: national map

  1. su_italy_934MB
  2. su_italy_lowres_210MB

Italy: landslide susceptibility maps

  1. susc_italy_880MB
  2. susc_italy_lowres_250MB

Himalaya (mostly Nepal)

  1. su_himalaya


Requirements, installation and run



The software have been tested starting on Ubuntu 14.04 LTS server but        
should run on a generic GNU/Linux machine.                
	Requirements: our software require GRASS GIS 7.*, Python, Bash.                
	The two files contained in the tar.gz archives (one python script, one bash script) must be copied        
	in the “scripts” folder of the GRASS GIS installation directory. They must be executable (see below).        
	A typical approach, for the installation, is (replace grass78 for previous versions):               

	# open a bash shell               

	# change working directory to the download folder, e.g.:                

	cd /home/$USER/Downloads                

	# move the files into the scripts folder of the grass installation, e.g.:         

	mv r.slopeunits /usr/lib/grass78/scripts          
mv /usr/lib/grass78/scripts # give execution rights chmod ugo+x /usr/lib/grass78/scripts/r.slopeunits chmod ugo+x /usr/lib/grass78/scripts/ # run GRASS GIS 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 ( # and: M. Alvioli, F. Guzzetti, I.Marchesini ( # and references therein for explanations, examples and additional options. # # please address comments, questions and bug fixes rquests either to: # ivan.marchesini[AT]; # massimiliano.alvioli[AT] #



  • Alvioli M., Guzzetti F., Marchesini I., (2020).
    Parameter-free delineation of slope units and terrain subdivision of Italy.
    Geomorphology 258, 107124.

  • 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.

  • Alvioli M., Marchesini I., Pokharel B., Gnywali K.R., Lim S. (2022).
    Geomorphological slope units of the Himalayas.
    Journal of Maps (2022).

  •  Pokharel B., Alvioli M., Lim S. (2021).
    Assessment of earthquake-induced landslide inventories and susceptibility maps using slope unit-based logistic regression and geospatial statistics.
    Scientific Reports 11, 21333.

  • Loche M., Alvioli M., Marchesini I., Bakka H., Lombardo L. (2022).
    Landslide susceptibility maps of Italy: lesson learnt from dealing with multiple landslide classes and the uneven spatial distribution of the national inventory
    Under review (preprint:

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published on 2021/12/20 15:59:00 GMT+2 last modified 2022-05-09T12:39:30+02:00