The use of the GIS into the Forest Fire prediction. The Simulation Model

The mastery of strategies of forests fire-fighting passes compulsorily by deep knowledge of forest fire phenomenon. One of the efficient means of apprehension of the forest fire, is to dispose of a tool that is capable to inform us about the behavior of fire before its apparition according to the given climatic conditions. In this context, the simulation remains an effective tool for the prediction of the fire behavior. It permits to determine with a relative confidence degree, susceptible zones to be ravaged by the fire during a determined period. The objective of this work is the study of mechanisms of forest fire progression by the elaboration of an automatic tool capable to pattern suitably a fire forest, its parameters, its propagation and its behavior in a given region. Through out this study, it will make conspicuous the considerable property (perhaps unavoidable) the Geographical information Systems (GIS), in combination with techniques of simulation in the apprehension of a problematical " fires forest " [DAG 94]. This resides in the power of the GIS to modelling all phenomenon presenting a geographical character. The interest that presents such a survey for operators in charge of the management of a forest fire (Fireman department, services of forests, local collectivities, etc.) is double. It permits to define to the long term a homogeneous and coherent politics of forest fire prevention, whereas the system permits to verify the adequacy of amenities and presents infrastructures of wrestling against the fire with the reality of a disaster [DAG 97]. It also allows to determine, in the perspective of the beginning of a fire, means to put in work for a coordination of intervention teams and a strategy that remains efficient, of wrestling against the fire progression II / Problematic: A lot of countries confronted to problems of forest fire seized the interest to resort to modern techniques of science to control and to master the forest fire that is source of permanent danger for the nature, the environment and the man's security. Countries as Canada, USA, France, Germany, Austria, etc., have started during the years 70 the study and the development of relative computer systems to a thematic " forest fires ". In the panoply of developed tools, models of propagation represent an appreciable part. Indeed, to fight a forest fire efficiently, a fire passes cumpulsorily by the understanding of mechanisms governing its propagation. Among techniques used for the propagation phenomenon study, the simulation holds a preponderant place. III / The simulation: The simulation of a phenomenon, is the operation that consists to study its behavior in situations generated by virtual data, to master it better in the real cases. The simulation permits to foresee the evolution of the phenomenon, once conditions of its manifestation are present. However, the simulation can never substitute itself for the reality, even though it permits to approach it. The process of simulation has for objective to reinforce the degree of confidence of the good working of the system put in place and no to validate it. In the case of a fire forest, the simulation is connected to the conception of an automatic process capable to inform us about the propagation of fire according to criterias defining a given climatic and environmental state [LEN98]. Values of these criterias describe a virtual situation connected to a real experimentation condition. It is right to confront results obtained with confirmed statistics that are able to bring the necessary corrections for a good calibration of the process. The description of forest fire situation requires the collection of data land (relief, vegetation, dwelling, electric networks,...) and the collection of climate data (wind, humidity, temperature,...). We speak then of parameters of definition of forest fire IV / Parameters of forest fire definition : The forest fire integrates the ambient air and draw its fuel in the plantable setting. Wind constitutes its principal vector. The shape of the land where it appears, contributes to its development and extension. In this context, the main factors intervening in the evolution of a forest fire, are according to SHERLIS [SHE96] and MISSOUMI [MIS97] strength and the direction of wind, the degree of inflammability of the plantable setting, the importance and the orientation of the slope and the starting point of fire. IV.1 / wind: It represents one of the fundamental factors (probably the main) in the process of evolution of fire. Its force, influences directly the fire propagation velocity and its direction determines the orientation of fire. The measurement of the wind is a climatological information provided according to two data: speed in km/h and orientation in a cardinal direction. IV.2 / vegetable cover : The vegetable species have a different sensitivity towards fire. Indeed, the "Alep Pine" differently burns (more or less quickly) than the "Oak cork" or the "the Eucalyptus". This sensitivity of the vegetable species with respect to fire is characterized by two indicators which are the degree of inflammability (DI) and the index of combustibility (IC). These indicators can be obtained, once the spieces of vegetation correctly specified. In our case, the identification of spieces is released by techniques of Remote Sensing from satellite images. IV.3 / relief: Fire acts differently on a ground according to whether it is flat or presenting very marked asperities (broken relief). A coherent process of simulation, must take into account the direction and the degree of the slope. The relief is generally represented by a Digital Terrain Model (DTM). Its generation rises from the altimetric data of ground such as the slope and the elevation. IV.4 / the starting point of fire: Lastly, any forest fire emanates from a starting point which is advisable to specify. The algorithms of calculation of the area devastated by fire in the process of simulation takes as initial point, the starting point of fire. The geographical co-ordinates of the starting point must be known. V / Presentation of the study: Our study, will initially presents a short overview of the existing models of propagation per simulation. It will note the contribution of a Geographical Information system (GIS) in the development of a model of forest fire simulation. The recourse to the GIS is justified by the geographical nature of the data relating to forest fire, such as data of ground, relief and ground occupation, and by the capacities of the GIS to integrate suitably all the parameters intervening in fire. Moreover, the tools of the graph theory and mathematical models necessary for simulation, are usual components in the GIS tools. V.1 / Model of simulation of propagation of forest fire: A model of propagation of forest fire, if it wants to be rigorous and precise, must integrate all factors of definition of the fire. Several models exist throughout the world characterizing the propagation of forest fire. Nevertheless, three classes of models appear according to the level of integration of the factors of propagation of fire. These models are identified much more with the space forms generated by simulation. Thus we find the pseudo-conical models, concentric models, and the polygonal models. V.1.1 / Concentric Model [ PAR90 ]: In this type of model, the prevalent parameter is the force of the wind. In fact, the process of simulation takes into account only the factor forces wind associated with the starting point with fire. The result obtained by this type of model is a series of concentric circles representing an approximation of the zones touched by the fire and which extent is a function of the evolution in time. "FIRES" developed by the laboratory of bio-forestry of the UQAT (Université du Québec A Trois Rivières) [QUE 91], is undoubtedly the first prototype of this type of model. It was developed in Canada, for the account of Park-Canada, organization responsible for the forests and green parks of Canada. It was tested during several years in the province of the "Territory of North", where it gave mitigated results [GAU 93]. The model of simulation is articulated around a simple approximation where the starting point of fire constitutes the center of the circle and the ray is determined by: