r.randomwalk is a flexible and multi-functional conceptual tool for backward- and forward-analyses of mass movement propagation. Mass points are routed from defined release pixels of one to many mass movements through a digital elevation model until a defined break criterion is reached. Lateral spreading is ensured by a constrained random walk approach. Compared to existing tools, the major innovative features of r.randomwalk are:
- multiple break criteria can be combined to compute an impact indicator score;
- the uncertainties of break criteria can be considered by performing multiple parallel computations with randomized parameter settings, resulting in an impact indicator index in the range 0-1;
- the results can be validated against observations and visualized (built-in functions to do so are available);
- observed landslides can be back-analyzed to derive the density distribution of the observed angles of reach. This distribution can be employed to compute an impact probability for each pixel.
Further, impact indicator scores and probabilities can be combined with release indicator scores or probabilities. Risk indicator scores can be computed if possible objects at risk are given.
r.randomwalk is open source, distributed under the GNU General Public License. It builds on GRASS GIS and the R Project for Statistical Computing. Note that r.randomwalk currently only works on UNIX systems (Ubuntu LTS 12.04 is recommended) with GRASS GIS 7.0 installed from source.
The key concepts of r.randomwalk and various tests for specific areas are laid down in detail in the following publication:
Below you can find the model code, the manual and the data (as far as it may be freely distributed) needed to reproduce the computations performed for the test areas in Mergili et al. (2015).
Please consult the manual of r.randomwalk provided along with the code and the relevant publications before starting to use the tool. If you encounter issues not covered by the manual, you are highly welcome to join the forum on r.randomwalk at landslidemodels.org.
Note that the efficient use of r.randomwalk requires some computational skills. If necessary, please acquire the relevant knowledge on Linux, GRASS GIS, and GIS in general before starting to work with r.randomwalk or posting in the forum.
Code and manual
Extract the source code and place the folder r.randomwalk somewhere into your home directory. Do not change the internal structure of the folder or the names of the files. Refer to the manual for instructions how to install r.randomwalk.
Release files and start scripts are available for all test areas in Publication 2. GRASS Locations are provided for those test areas where the data may be freely distributed. Perform the following steps to run r.randomwalk for one of those areas:
- Extract the GRASS Location somewhere into your home directory and open GRASS 7.0 with this location.
- Save the release file and the start script into any place in your home directory. It is, however, important that both files are placed in the same directory.
- Within GRASS, use the command line terminal to change to the directory with the start script and the release file, and to execute the start script with 'sh scriptname'. scriptname stands for the name of the start script of the corresponding test area. All results will be placed in the current directory and in the active GRASS Location.
Instead of starting r.randomwalk with a start script, you could also use the command line or a simple graphical user interface (by just entering 'r.randomwalk' in the command line). With the given start scripts you can easily combine multiple calculations, and you should be able to reproduce the results presented in Publication 2 (even though there will be some minor differences due to randomization). You may manipulate the start scripts in order to explore how changes in the parameter settings influence the model results and the computational times. Please refer to the manual for details with regard to the flags and parameters.