Coupled atmosphere-fire simulations of the FireFlux experiment: Impacts of model resolution on its performance

Even though the scales and intensities of grass fires are not as great as forest fires, grass fires can present serious threats to firefighters and communities. Due to their very high spread rates they may be difficult to confine, and when they run out of control they can severely affect communities located within grassland environments. The ability to forecast grass fire spread could be of a great importance for agencies making decisions about prescribed burns. The regular spot forecasts may not provide enough information to predict spatial fire behavior, especially in terrain where meteorological conditions are not uniform. Coupled atmosphere-fire models are good candidates for providing realistic fire spread forecasts, but their usefulness is limited by the time required for completing the coupled atmosphere-fire simulations. In this study we analyze the sensitivity of a coupled-atmospheric model with respect to the sizes of the atmospheric and fire model grid meshes. Based on observations of the plume properties recorded during the FireFlux experiment (Clements et al. 2007), we try to establish the optimal model configuration that provides realistic results for the least computational expense. We investigate the limitations in the model and propose possible solutions that could accelerate simulations, while allowing for realistic rendering of fire behavior. The model used in his study extends WRF-Fire in WRF 3.3, and it is available from openwfm.org. It combines the Weather Research and Forecasting model (WRF) with a fire code implementing a semi-empirical surface fire behavior model that calculates the rate of spread of the fire line based on fuel properties, wind velocities from WRF, and terrain slope.