A heat transfer simulation model for wildfire spread

A new approach to fire spread simulation based on heat transfer events is described. The new simulation model is patch based with irregular patch shapes and sizes, which overcomes the influence of grid geometry on fire shape. It captures fire behaviour phenomena such as point fire acceleration and the dependence of fire rate of spread on line fire width. The new event based simulation model is efficient since the computational effort is focussed on the fire front where the majority of heat transfer takes place. It captures a wider range of fire behaviour phenomena than fire front propagation systems as it allows interaction between neighbouring parts of the fire, unlike the Huygens’ principle approach which disregards such interaction. In the simulation model, each patch represents a parcel of land with state parameters for fuel type, load and moisture, temperature and burning state. When the temperature of an unburnt patch reaches ignition temperature, it changes from a flammable state where heat received is converted into temperature change, to a burning state where fuel is converted into generated heat. When all fuel in a patch is consumed, the patch changes state to burnt. The frequency of heat transfer events between neighbouring patches, that is, the rate of heat transfer, depends on the temperature gradient and properties of the communication links connecting them. The effective conductivity of the inter-patch links are dynamic and are influenced by slope, wind speed and direction. An important step in creating the simulation model is to calibrate the internal simulation arameters, which capture the rates of heat generation, heat transfer and heat consumption, against a fire behaviour model for each fuel type present in the landscape. This creates a mapping between environmental parameters such as wind speed, direction, slope and fuel moisture and the internal simulation parameters, so that for a given fuel type and environmental parameters, the correct fire spread rate is predicted by the simulation model. Initial results given by this new heat transfer simulation model are demonstrated via simple wildfire scenarios and by using data from an extreme grass fire with actual fuel, ignition and weather data.