Higrad/Firetec, Multiple Fuel Types: Approach, Implementation, and Idealized Scenarios

The coupled atmospheric dynamics-wildfire model, HIGRAD/FIRETEC, is extended to allow for representation of multiple fuel types within a single computational grid cell. Previously model fuel characteristics were averaged quantities over the entire cell volume. Important traits such as bulk density, moisture content, and length scale were necessarily represented by a homogeneous distribution over the cell volume. For example simulation of a fuel bed consisting of tall dry grass intermingled amongst a shorter layer of less dry duff or litter, would require a single value of average density, and mass weighted averages of fuel bed depth, moisture content and characteristic size scale. This process of averaging fuel load characteristics may produce results that less accurately represent real world fuel beds. This talk describes in detail functional extensions to the model which allow representation of multiple fuel types within a single cell volume. Results from idealized scenarios yield insights into the dynamics of wildfire within a mixed fuel bed. Moreover these results show that local effects of overlapping fuel types on wind drag, convective heat exchange, thermal radiation emission/absorption, and combustion rate, can lead to large scale changes in overall fire behavior such as spread rate, area burned, and fuel depletion.