Global sensitivity analysis and scale effects of a fire propagation model used over Mediterranean shrublands

A Global Sensitivity Analysis (GSA) and an analysis of scale effects have been carried out over the equations given by Rothermel (1972), with some additional modifications. Data mainly derived from Mediterranean shrublands and a spatially close meteorological station have been used to derive probability distribution functions for the variables involved. In spite of the abundant non-linearities contained in the equations studied, scale effects found have been relatively unimportant, thus supporting the current usage of spatial averages (i.e. fuel models) in spatially distributed models based on the Rothermel equations. On the other hand, the results of the GSA clearly showed the negligible effect of the variability of three of the model variables (the low heat content, the particle density and the mineral content) on the output values. However, all other input variables had some noticeable effect over the variability of the output, and they cannot be ignored if an optimal use of the model is desired. Finally, caution is recommended if results have to be extrapolated to other types of vegetation or climate.