Source Code for the EMBYR Wildfire Simulation Model

William W. Hargrove and Robert H. Gardner

EMBYR is an acronym for ``Ecological Model for Burning the Yellowstone Region'' EMBYR was designed to simulate wildfires, the subsequent pattern of vegetation, and then the next generation of burn patterns. The EMBYR simulation is intended to explore the landscape ecology of burn patterns over large spatial scales and long periods of time. As such, pixel-by-pixel simulation accuracy is not emphasized; however, extensive effort has been made to obtain the right answer at landscape scales. EMBYR is not a firefighting tool;nevertheless, the model may be of some value for such uses.

We have come to view wildfire as a stochastic phenomenon. Particular historical fires represent one realization from a spectrum of possible statistical behaviors. Firefighters often share this view of wildfire. They speak about unrealized fire behavior in the past, and predict alternative fire behaviors in the future. While the EMBYR model parameters could be adjusted to reproduce a particular historical wildfire exactly, it is more important to reproduce any wildfire relatively well on average.

In keeping with this philosophical view, EMBYR can generate "Risk Maps", which are constructed from many replications of a single simulated fire. Cells which burned in many of the replications are colored black, while cells which burned in only a few simulations are colored white, with gray levels in intermediate cases. Such a Risk Map portrays the statistical suite of possible wildfire behavior in a single map.

Terms of Use and Distribution

The EMBYR source code package is distributed under the same terms as the Gnu Copyleft agreement Copyleft basically says that anyone who redistributes the software, with or without changes, must pass along the freedom to further copy and change it.

There are two additional requests that we make beyond those of the Copyleft agreement: (1) please notify us of improvements made in the code, and allow the improved versions to be distributed here, and (2) papers resulting from the use of the EMBYR simulation or code should cite the two papers listed below:

Hargrove, W.W., R.H. Gardner, M.G. Turner, W.H. Romme, and D.G. Despain. 2000. Simulating fire patterns in heterogeneous landscapes. Ecological Modelling 135(2-3):243-263. Click here to download preprint in pdf format or in Postscript format.

Gardner, R.H., W.W. Hargrove, M.G. Turner, and W.H. Romme. 1996. Climate change, disturbances, and landscape dynamics. Pages 149-172 In: B. Walker and W. Steffen (eds.) Global Change and Terrestrial Ecosystems. International Geosphere-Biosphere Programme Book Series - Book #2. Cambridge University Press, Cambridge, Great Britain. 619 pgs.

The first paper describes in detail the workings of the EMBYR model. The second describes results from a set of 1000-year wildfire simulations of Yellowstone (10 replicates each) under a nominal, a dry, and a wet future weather scenario.

If you agree to all of the above terms, click here to download the EMBYR distribution package in gzipped tar format.

The EMBYR code is written in FORTRAN 77, and is contained within a main visualization routine written in C by Forrest Hoffman. EMBYR is a stand-alone simulation, and is not dependent on any GIS package. However, it is designed to work especially well with the GRASS GIS system. EMBYR is event-driven, meaning that the simulation immediately jumps forward to the next future ignition when the last burning cell goes out. The EMBYR model also has variable time-steps. This allows finer temporal resolution while simulating the burning of high-quality fuels. There are many explanatory comments throughout the code.

System Requirements for EMBYR:

Unix/LINUX environment
XPM extension to X windows installed
C compiler
FORTRAN compiler

The XPM X PixMap library, is used by EMBYR for visualizing maps of the burn on screen during the simulation. The XPM X PixMap library was written by Arnaud LeHors.

XPixMap (XPM) consists of an ASCII image format and a C library. The format defines how to store color images (X Pixmap) in a portable and powerful way. The library provides a set of functions to store and retrieve images to and from XPM format data, being either files, buffers (files in memory), or data (included files).

While XPM is not an X Consortium standard, it is already a de facto standard. It is used in many applications both commercial and non-commercial. There is a mailing list to talk about XPM. This is

You may already have the XPM extension installed on your machine. Several computer manufacturers distribute the XPM library, as contributed software, on the platforms they sell. Several flavors of the LINUX operating system also come with the XPM extension already installed.

Compiling the EMBYR Model

Two Makefiles are provided: one for compilers supporting function prototyping, and one without function prototyping. Copy the appropriate Makefile to Makefile, then type:

make fire

The Makefile also supports compilation of debugging and profiling objects. The name of the executable is fire. If you make platform-specific changes to the Makefile, please return it to me so that I can include it in the distribution. There is no point in others duplicating your work.

File Names and Extensions Associated with the EMBYR Model

File Name or Extension Associated Function in EMBYR
*.i array sizes
*.h header files
*.matrix model parameters
*.cmp color maps
*.scr demo scripts
*.fuel fuel maps
*.elev elevation maps
wx.* or weather.* weather sequence files
ign.* or ignition.* ignition locations and times

Running the EMBYR Model

The EMBYR model has many options, and some of these are mutually exclusive. The simulation can generate its own fuel layer, continuous or gradient, or it can read a fuel and elevation layer prepared from a GIS. The model can generate random or fixed ignitions, or it can read a sequence of spatial ignitions through time. Weather can be static throughout the simulation, or EMBYR can read a changing weather sequence through time. At present, weather conditions are uniform across the fuelscape.

Simply running the executable begins a cascade of questions from the model which query the user to set up the options for the simulation run. Responses to the questions direct the subsequent questions, changing the way that the option tree is traversed. This verbose interaction mode is a good way to become familiar with the wide array of EMBYR options. After all questions are answered, the simulation begins.

Because answering all of the input questions for each run would be tedious, EMBYR writes a script file, fire.scr, containing the input answers from the last run. Thus, the last simulation can be repeated by issuing the command:

fire < fire.scr

To change a few input settings, it is not necessary to wade through all of the input questions again. Instead, simply edit the fire.scr script file directly, and then rerun the simulation using the modified script file. Mnemonic comments within the script file aid in such editing process.

A number of demonstration .scr script files are included in the distribution, and running these ``canned'' demos is a good way to test the installation, as well as to see the capabilities of the EMBYR model. Intermediate and final burn maps can be output in several formats, including XPM and GRASS.

Click here to see EMBYR used to simulate the Forest Lake fire in Yellowstone in 1981.

Image Gallery of EMBYR Results

These images show individual simulations of historical fires that occurred in Yellowstone during the 1981 fire season. Rather than fitting parameters for each fire individually, these results were obtained from a single parameter set which was optimized over all fires. Most images show a composite with the actual perimeter of the historical fire in red, a single simulation of the burn, and a risk map showing the statistical behavior of the simulated fire. The Greater Yellowstone Area after the 1981 fire season is shown in the image at the top of the page.

Sulphur/Astringent fire

Two Ocean fire

Witch fire

Pelican fire No historical perimeter available.

Creek/Mountain fire No historical perimeter available.

Turbid/Basin/Divide fires It is as important to simulate such historically small fires correctly as to get the large events right.

For additional information contact:

William W. Hargrove
Oak Ridge National Laboratory
GIS and Spatial Technologies Group
Computational Physics and Engineering Division
P.O. Box 2008, M.S. 6274
Oak Ridge, TN 37831-6274
865-241-2748 voice
865-241-3870 fax
Robert H. Gardner
Appalachian Laboratory
301 Braddock Road
Frostburg, MD 21532
301-689-7125 voice
301-689-7200 fax

William W. Hargrove (
Last Modified: Thu Sep 21 13:34:41 EDT 2000