Researchers have been using models to predict and study wildfire behavior for approximately fifty years. These models range in complexity from simple algebraic models that may be 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 based on environmental conditions of the modeled fires, the completeness of the available fuels and weather data, the computational resources available,and the time urgency of the results. 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 a transport formulation and is therefore capable of accounting for time and space history. We are using FIRETEC in conjunction with a sophisticated fine-scale atmospheric model, HIGRAD, to examine some of the complexities of wildfire behavior that are difficult to study with simpler 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 efects of different vertical 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 inhomogeneous terrain 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. Recently we have been using FIRETEC to look at the effects of moisture on wildfire behavior. The qualitative effects of moisture on many aspects of wildflres has been known for many years, but models like FIRETEC give us tools to examine wildfire responses to moisture quantitatively and in greater detail. 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. © University of Idaho 2000. Abstract reproduced by permission.