National Wildfire Coordinating Group

Nelson Model

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The Nelson dead-fuel moisture model

The ‘Nelson model’ for Dead Fuel Models is a physical-based model that contains equations for heat and moisture transfer (Nelson 2000). Besides internal water, it also takes into account water at the surface through the processes of adsorption, desorption, rainfall, condensation, and evaporation. Inputs to the Nelson model include air temperature, relative humidity, solar radiation, and amount of rainfall since the last observation. Outputs include moisture content and temperature of the fuel stick at the times corresponding to the weather data inputs. The theoretical model was converted into a finite-difference numerical model, so as to be usable in practice.

Nelson Dead Fuel Classes

Time Lag Stick Radius
1 hour 0.08 in (0.2cm)
10 hour 0.25 in (0.64cm)
100 hour 0.8 in (2.0cm)
1000 hour 2.5 in (6.4cm)


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