From Fundamental Knowledge on Forest Fires

to behavioural description and prediction

A. SIMEONI and P.A. SANTONI

ERT “Feux”, SPE – CNRS UMR 6134, Università di Corsica, BP 52,

20250 Corti, Corsica, France. Phone: 00 (33) 4 95 45 01 61,

fax: 00 (33) 4 95 45 01 62, e-mail: simeoni@univ-corse.fr

The problem of forest fire modelling can be tackled in two ways. The first one concerns the models of knowledge [1] that allow to increase the fundamental knowledge and the understanding of forest fires. Such models try to describe the physics involved in fire spread in the finest way. The second one concerns the description of the fire behaviour in order to make predictions. Such models deal with the description of some macroscopic properties of the fire, as front shape and rate of spread. The more detailed are based on a physical description of the fire, but in a simpler way than the first ones.

These two aspects of modelling are strongly linked together. Indeed, to describe the fire spread in a simple way, it is necessary to understand well its behaviour. So, excepted if a statistical description is chosen, a fundamental knowledge is essential in order to make the appropriate assumptions and simplifications to create the model of behaviour.

Our research team has chosen this last approach. Indeed, our aim is to propose a management tool which provides the necessary information concerning the spreading of a wildland fire (rate of spread, fire front geometry and temperature field). In light of this, we have developed a semi-empirical model of fire spread across a fuel bed which is unsteady and two-dimensional along the ground shape [2]. This model should be used as a tool to help the fire fighters to make the appropriate decisions and the forest managers to make their working plans.

The model describes correctly the different configurations of slope and wind at laboratory scale through pine needle fuel beds. To reach this goal, we had to improve it by making the appropriate simple description. To proceed, we used a multiphase model as reference of modelling [1], as it describes the physics involved in forest fires in the finest way. Our approach consists in reducing it [3], for example to obtain a simplified flow that allows to improve the description of fire under wind conditions [4]. To complete our approach, we study in detail each phenomenon that we need to include in our model, in order to increase our fundamental knowledge to be sure that we make the appropriate simplifications.

In our talk, we will present our modelling approach and an application to wind effect description, as well as some perspectives brought by this approach.

[1] Larini, M., Giroux F., Porterie B., and Loraud J.C. A multiphase formulation for fire propagation in heterogeneous combustible media. Int. J. of Heat and Mass Transfer, 41 (1997) 881-897.

[2] Santoni, P. A., Balbi, J. H. and Dupuy, J.L. Dynamic modelling of upslope fire growth. Int. J. of Wildland Fire. 9 (1999) 285-292.

[3] Simeoni, A., Santoni, P.A., Larini, M., and Balbi, J.H. Proposal for Theoretical Improvement of Semi-Physical Forest Fire Spread Models Thanks to a Multiphase Approach: Application to a Fire Spread Model Across a Fuel Bed. Comb. Sci. and Tech. 162 (2001) 59-84.

[4] Simeoni, A., Santoni, P.A., Larini, M. and Balbi J.H. Reduction of a multiphase formulation to include a simplified flow in a semi-physical model of fire spread across a fuel bed. Int. J. of Thermal Sci. 42 (2003) 95-105.