Physical Parametrisation of Fire-Spotting for Operational Wildfire Simulators

Abstract

AbstractFire-spotting is strongly affected by mean wind and fire intensity, not only because they characterise the transport of firebrands, but, also, because they change the geometry of the flame, namely, the flame height and the flame length. Interdependencies between the flame length and the fire intensity are discussed in literature by a number of empirical relations. In the present study, the energy conservation principle and the energy flow rate in the convection column above the fire line are considered in order to establish the relation between the flame geometry and the fire line intensity in wildfires. Moreover, in opposition to literature, the derived formula allows for stating the rate of spread of the fire propagation in terms of the flame geometry factors by taking into account also the effects of the horizontal mean wind and the terrain slope. Numerical examples show that fire-spotting is strongly impacted by the flame geometry, which is specified by the fuel and vegetation, and then it cannot be neglected in the physical parametrisation of the phenomenon.