A QUALITATIVE COMPARISON OF FIRE SPREAD MODELS INCORPORATING WIND ANDSLOPE EFFECTS

Wind velocity and slope are two critical variables that affect wildlan d five rate of spread, The effects of these variables on rate of sprea d are often combined in rate-of-spread models using vector addition, T he various methods used to combine wind and slope effects have seldom been validated or compared due to differences in the models or to lack of data. In this study, rate-of-spread predictions from the Canadian Fire Behavior Prediction (FBP) system, McArthur's Mark V forest fire d anger meter, the Rothermel empirical model, and the Pagni and Peterson physical model were compared with spread rates observed in a designed laboratory experiment in which wind velocity and slope were varied, M ethods of combining wind and slope developed by Albini, McAlpine, and Rothermel were applied to two forms of Rothermel's model. Rothermel's model (original and modified) coupled with Albini's method and Pagni's model predictions closely reproduced the observed shape of the rate-o f-spread response to wind and slope, Rothermel's method and McAlpine's method worked well in all cases except in upslope spread with opposed flow. However, Rothermel's model failed to predict a nonzero rate of spread in fuel beds with moisture contents of 35%. Possible causes of overprediction by McArthur's model and the FBP model included: (1) app lication of equations derived from full-scale fives to laboratory-scal e fives, (2) improper selection of fuel type to represent artificial f uel beds, and (3) inaccurate estimation of wind velocity 10 m above th e vegetation surface using a logarithmic profile.