r.ros - GRASS manual
Author: GRASS Development Team
Description: r.ros: Generates three, or four raster map layers showing the base (perpendicular) rate of spread (ROS), the maximum (forward) ROS, the direction of the maximum ROS, and optionally the maximum potential spotting distance for fire spread simulation.
Keywords: raster, fire, spread, rate of spread, hazard, model

## NAME

r.ros - Generates rate of spread raster maps.
Generates three, or four raster map layers showing the base (perpendicular) rate of spread (ROS), the maximum (forward) ROS, the direction of the maximum ROS, and optionally the maximum potential spotting distance for fire spread simulation.

## KEYWORDS

raster, fire, spread, rate of spread, hazard, model

## SYNOPSIS

r.ros
r.ros --help
r.ros model=name [moisture_1h=name] [moisture_10h=name] [moisture_100h=name] moisture_live=name [velocity=name] [direction=name] [slope=name] [aspect=name] [elevation=name] base_ros=name max_ros=name direction_ros=name [spotting_distance=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

### Flags:

--overwrite
  Allow output files to overwrite existing files
--help
  Print usage summary
--verbose
  Verbose module output
--quiet
  Quiet module output
--ui
  Force launching GUI dialog

### Parameters:

model=name [required]
  Raster map containing fuel models
  Name of an existing raster map layer in the user's current mapset search path containing the standard fuel models defined by the USDA Forest Service. Valid values are 1-13; other numbers are recognized as barriers by r.ros.
moisture_1h=name
  Raster map containing the 1-hour fuel moisture (%)
  Name of an existing raster map layer in the user's current mapset search path containing the 1-hour (<.25") fuel moisture (percentage content multiplied by 100).
moisture_10h=name
  Raster map containing the 10-hour fuel moisture (%)
  Name of an existing raster map layer in the user's current mapset search path containing the 10-hour (.25-1") fuel moisture (percentage content multiplied by 100).
moisture_100h=name
  Raster map containing the 100-hour fuel moisture (%)
  Name of an existing raster map layer in the user's current mapset search path containing the 100-hour (1-3") fuel moisture (percentage content multiplied by 100).
moisture_live=name [required]
  Raster map containing live fuel moisture (%)
  Name of an existing raster map layer in the user's current mapset search path containing live (herbaceous) fuel moisture (percentage content multiplied by 100).
velocity=name
  Raster map containing midflame wind velocities (ft/min)
  Name of an existing raster map layer in the user's current mapset search path containing wind velocities at half of the average flame height (feet/minute).
direction=name
  Name of raster map containing wind directions (degree)
  Name of an existing raster map layer in the user's current mapset search path containing wind direction, clockwise from north (degree).
slope=name
  Name of raster map containing slope (degree)
  Name of an existing raster map layer in the user's current mapset search path containing topographic slope (degree).
aspect=name
  Raster map containing aspect (degree, CCW from E)
  Name of an existing raster map layer in the user's current mapset search path containing topographic aspect, counterclockwise from east (GRASS convention) in degrees.
elevation=name
  Raster map containing elevation (m, required for spotting)
  Name of an existing raster map layer in the user's current mapset search path containing elevation (meters). Option is required from spotting distance computation (when spotting_distance option is provided)
base_ros=name [required]
  Output raster map containing base ROS (cm/min)
  Base (perpendicular) rate of spread (ROS)
max_ros=name [required]
  Output raster map containing maximal ROS (cm/min)
  The maximum (forward) rate of spread (ROS)
direction_ros=name [required]
  Output raster map containing directions of maximal ROS (degree)
  The direction of the maximal (forward) rate of spread (ROS)
spotting_distance=name
  Output raster map containing maximal spotting distance (m)
  The maximal potential spotting distance (requires elevation raster map to be provided).

## DESCRIPTION

r.ros is part of the wildfire simulation toolset. Preparational steps for the fire simulation are the calculation of the rate of spread (ROS) with r.ros, and the creating of spread map with r.spread. Eventually, the fire path(s) based on starting point(s) are calculated with r.spreadpath.

r.ros is used for fire (wildfire) modeling. The input is fuel model and moisture and the outputs are rate of spread (ROS) values. The module generates the base ROS value, maximum ROS value, direction of the maximum ROS, and optionally the maximum potential spotting distance of wildfire for each raster cell in the current geographic region. These three or four raster map layers serve as inputs for the r.spread module which is the next step in fire simulation.

The r.ros module and two related modules r.spread, and r.spreadpath can be used not only for wildfire modeling but also generally to simulate other events where spread of something is involved and elliptical spread is appropriate.

The calculation of the two ROS values for each raster cell is based on the Fortran code by Pat Andrews (1983) of the Northern Forest Fire Laboratory, USDA Forest Service. The direction of the maximum ROS results from the vector addition of the forward ROS in wind direction and that in upslope direction. The spotting distance, if required, will be calculated by a separate function, spot_dist(), which is based on Lathrop and Xu (in preparation), Chase (1984) and Rothermel (1991). More information on r.ros and r.spread can be found in Xu (1994).

The output parameter is a basename (prefix) for all generated raster maps and each map gets a unique suffix:

- `.base` for the base (perpendicular) ROS (cm/minute)
- `.max` for the maximum (forward) ROS (cm/minute),
- `.maxdir` for the direction of the maximum ROS, clockwise from north (degree), and optionally
- `.spotdist` for the maximum potential spotting distance (meters).

So, if the output parameter is `blackforest_ros`, r.ros creates `blackforest_ros.base`, `blackforest_ros.max`, `blackforest_ros.maxdir`, and (optionally) `blackforest_ros.spotdist` raster maps.

If only one or two of the options moisture_1h, moisture_10h, and moisture_100h are given, the module will assign values to the missing option using the formula:

    moisture_100h = moisture_10h + 1 = moisture_1h + 2

However, at least one of them should be given.

Options velocity and direction must be both given or both omitted. If none is given, the module will assume a no-wind condition.

Options slope and aspect must be also given together. If none is given, the module will assume a topographically flat condition. Option elevation must be given if -s (spotting) flag is used.

## EXAMPLES

Assume we have inputs, the following generates ROSes and spotting distances:

    r.ros -s model=fire_model moisture_1h=1hour_moisture moisture_live=live_moisture \
        velocity=wind_speed direction=wind_direction \
        slope=slope aspect=aspect elevation=elevation output=ros

## NOTES

1. r.ros is supposed to be run before running r.spread module. The combination of these two modules forms a simulation of the spread of wildfires.
2. The user should be sure that the inputs to r.ros are in proper units.
3. The output units for the base and maximum ROSes are in cm/minute rather than ft/minute, which is due to that a possible zero ft/minute base ROS value and a positive integer ft/minute maximum ROS would result in calculation failure in the r.spread module. As far as the user just use r.ros together with r.spread, there is no need to concern about these output units.

## REFERENCES

- Albini, F. A., 1976, Computer-based models of wildland fire behavior: a user's manual, USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, Utah.
- Andrews, P. L., 1986, BEHAVE: fire behavior prediction and fuel modeling system -- BURN subsystem, Part 1, USDA Forest Service, Intermountain Research Station, Gen. Tech. Rep. INT-194, Ogden, Utah.
- Chase, Carolyn, H., 1984, Spotting distance from wind-driven surface fires -- extensions of equations for pocket calculators, US Forest Service, Res. Note INT-346, Ogden, Utah.
- Lathrop, Richard G. and Jianping Xu, A geographic information system-based approach for calculating spotting distance. (in preparation)
- Rothermel, R. E., 1972, A mathematical model for predicting fire spread in wildland fuels, USDA Forest Service, Intermountain Forest and Range Experiment Station, Res. Pap. INT-115, Ogden, Utah.
- Rothermel, Richard, 1991, Predicting behavior and size of crown fires in the northern Rocky Mountains, US Forest Service, Res. Paper INT-438, Ogden, Utah.
- Xu, Jianping, 1994, Simulating the spread of wildfires using a geographic information system and remote sensing, Ph. D. Dissertation, Rutgers University, New Brunswick, Jersey (ref).

## SEE ALSO

g.region, r.slope.aspect, r.spread, r.spreadpath Sample data download: firedemo.sh (run this script within the "Fire simulation data set" project).

## AUTHOR

Jianping Xu, Center for Remote Sensing and Spatial Analysis, Rutgers University.

## SOURCE CODE

Available at: r.ros source code (history)

Latest change: Monday Feb 09 18:47:00 2026 in commit: fe51d3824fc8d5aa0e1ced4d9110214dc0192676

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