Semi-empirical Model for Fire Spread in Chamise and Big Sagebrush Shrubs with Spatially-Defined Fuel Elements and Flames

摘要

Current operational fire spread models are mostly based on experimental results from dead, low moisture fuel beds and thus do not perform well when modeling fire behavior in live shrubs. A previously-developed semi-empirical shrub combustion model was improved and expanded to treat live chamise and big sagebrush. Fire spread in live chamise and big sagebrush shrubs was measured in an open-roofed wind tunnel, which was used as the basis to develop the current model. Shrub geometry was modeled by coupling a Lindenmayer-systems (L-systems) approach with terrestrial LiDAR scan data. Wind speed was held constant at 1.4 m/s. Species specific correlations for physical properties and combustion characteristics of individual fuel element were incorporate in this model. Modeling results compared well with measured time-dependent fire behavior. Variations in local fuel density affected flame spread more than the overall fuel bed density. This model is an innovative approach to simulate shrub combustion via flame propagation at individual fuel element scale with a fairly low computational cost.