Studying Complex Wildfire Behavior Using FIRETEC

Wildfire models range in complexity from simple empirically-based algebraic models implemented in graphical form or on hand-held calculators to complex formulations that are implemented on large computers. The models of different complexities are appropriate for different applications. Many of the more complex models are not currently suitable for faster than real time applications because of their very computationally intensive nature, but their more complete nature allows them to be used to examine some of the more complex wildfire behaviors. FIRETEC is a wildfire behavior model being developed at Los Alamos National Laboratory and is based on conservation of mass, momentum, species, and energy. FIRETEC is combined with a sophisticated fine-scale atmospheric model, HIGRAD, to examine some of the complexities of wildfire behavior and its relationship to ambient winds. We are focusing on fire behaviors that result from physical phenomenon that can not be represented by simple fire models. Examples of the types of physical phenomenon that we are examining are the effects of transient wind conditions, the effects of inhomogeneous terrain, the effects of moisture on fire behavior in complex conditions, and the effects of different vertical vegetation structure on fire behavior.

Simulations performed with FIRETEC/HIGRAD show that the wildfire behavior is dependent not only on current wind conditions but also on the evolution of a wind field. We see that under certain evolving weather conditions it is impossible to predict the wildfire behavior without incorporating information about the history of the wind field. FIRETEC is being used to investigate the conditions under which it is necessary to incorporate the history of a transient wind field.

The effects of nonuniform terrain interaction with atmospheric winds on wildfires are also being examined with FIRETEC/HIGRAD. We are examining the non-local effects of terrain variations and investigating the terrain conditions where wildfire behavior models must incorporate more than just the slope at a particular location.

FIRETEC can be used to examine the complex set of conditions under which active and passive crown fires occur. Crown fire behavior is dependent on a variety of complex conditions such as canopy and understory fuel load and moisture content. However one of the most significant factors that control crown fire behavior is the atmospheric winds and their interaction with canopy and fire.

Until we reach the point where models such as FIRETEC can be used for operational purposes, we can use them to learn more about the physical processes that current operational models do not adequately represent. By studying these physical processes, we can better develop the simple models and determine situations where they are not appropriate and should be used with caution.