A Spread Simulation Demands a Gridded Landscape of Fuel, Canopy and Terrain
A single spread equation runs at a point. To grow a fire across country, a simulator needs the same inputs everywhere, supplied as aligned raster layers on one grid: a fuel model number per cell, elevation, slope and aspect from a terrain model, and canopy layers — cover, stand height, base height and bulk density — for the crown-fire test. In the US these are packaged as a landscape file and distributed nationally at 30 metre resolution. Two facts matter more than the file format. First, the grid resolution is a modelling choice with consequences: a 30 metre cell cannot represent a road, a stream or a fuel break narrower than 30 metres, so the model will happily spread a fire across a barrier that in reality would stop it. Second, the layers are a snapshot, often years old, while the fire is happening today; a stand that burned last season is still forest in the file. After this Concept you can list what a spread simulator must be given before it can run and name the two ways a landscape file misleads it.
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A single spread equation runs at a point. To grow a fire across country, a simulator needs the same inputs everywhere, supplied as aligned raster layers on one grid: a fuel model number per cell, elevation, slope and aspect from a terrain model, and canopy layers — cover, stand height, base height and bulk density — for the crown-fire test. In the US these are packaged as a landscape file and distributed nationally at 30 metre resolution. Two facts matter more than the file format. First, the grid resolution is a modelling choice with consequences: a 30 metre cell cannot represent a road, a stream or a fuel break narrower than 30 metres, so the model will happily spread a fire across a barrier that in reality would stop it. Second, the layers are a snapshot, often years old, while the fire is happening today; a stand that burned last season is still forest in the file. After this Concept you can list what a spread simulator must be given before it can run and name the two ways a landscape file misleads it.
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