Variations in Turbulence Characteristics of Head Fires Induced by Background Wind and Fuel Loading Levels

Abstract. Turbulence caused by wildfires can significantly alter the meteorological conditions in the fire area, which is a primary cause of the instability and unpredictability of fire behavior. Observing the differences in turbulence characteristics and propagation patterns caused by variations in fuel and background atmospheric conditions is crucial for the early warning of extreme fire behavior resulting from high-intensity fire-atmosphere interactions based on pre-fire information. This study, based on high-density measurements of fire-induced turbulence, examines how the differences in turbulence characteristics between the pre-burn, burning, and post-burn periods are influenced by variations in background mean wind speed and fuel load. It also investigates the impact on the spatial heterogeneity of turbulence characteristics, particularly their changes with increasing distance from the ignition boundary. Turbulence characteristics are quantified by parameters including instantaneous wind speed fluctuations, turbulent kinetic energy, heat flux, and momentum flux. The analysis indicates that the spatial heterogeneity of turbulence characteristics is weakened with increasing background wind speed; an increase in fuel load will result in a prolonged disturbance of atmospheric conditions by the fire; both increases in background wind speed and fuel load lead to the changes in the dominant components of certain parameters.