TRIGRS — The Complete Guide: Rainfall-Triggered Shallow Landslide Hazard Maps
TRIGRS is a USGS regional model of slope stability under rainfall. For every cell of a raster it calculates how infiltrating water changes pore pressure over time, and from that the infinite-slope factor of safety. The result is a map showing where, and at what point in a storm, shallow landslides are likely. The code is in the public domain and free for commercial work too.
TRIGRS
U.S. Geological Survey (USGS)
Grid-based regional slope-stability model for rainfall infiltration, used to forecast shallow landslides.
Get it from the vendorWhat you get
- Factor of safety per cell — infinite-slope maps through the rainfall event.
- Saturated and unsaturated soils — two infiltration modes chosen to match site conditions.
- Time-varying rainfall — changing intensities through the storm, not one fixed value.
- Surface-runoff routing — water that does not infiltrate moves on to downslope cells.
- Parallel version — MPI runs for large areas, plus utilities for preparing grids.
Who it suits and what to know
Geotechnical engineers and geologists producing hazard maps along roads or across catchments. It is a command-line program distributed as Fortran source, so you compile it and work with plain-text input files. Grids are prepared and inspected in GIS software, and result quality depends heavily on soil parameters and engineering judgement. It does not replace a stability analysis of an individual slope.
Related tools
For the stability of a single slope section — SSAP. For preparing slope and soil-depth grids and viewing results — QGIS. For terrain derivatives and catchment delineation — WhiteboxTools.
SSAP — Slope Stability Analysis
Lorenzo Borselli, Università di San Luis Potosí
Limit equilibrium slope stability analysis, with automatic search for the critical surface.
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QGIS
QGIS.org
Open-source GIS for spatial analysis, layer work and map production.
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WhiteboxTools
Whitebox Geospatial
Hundreds of geospatial analysis tools, especially strong on terrain and LiDAR point clouds.
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SAGA GIS
SAGA Development Team
Advanced spatial analysis, especially on elevation models and terrain.
Get it from the vendorThe bottom line
TRIGRS is a well-known research tool for mapping rainfall-induced landslide hazard. It needs GIS preparation and comfort with the command line, but it is free and fully transparent.