Effects of small scale heterogeneity of vegetation on radiative transfer in forest fire

Abstract

Wildland fires are driven by vegetation which is a medium that can be very heterogeneous at several scales. These heterogeneities from shoot to stand levels are likely to affect fire behavior. In the context of theoretical fire modelling, we investigated the effects of departure from randomness in radiative transfer. A methodology derived from approach in other turbid media for solar radiation was adapted to our problem. From several Mediterranean fuel type calculations, conditions on vegetation parameters that provide heterogeneity effects were exhibited. Fuel description was done from field measurements and plant architecture modelling. Results show that both a strong spatial variation in fuel distribution and vegetation dense enough were required to provide heterogeneity effects. The combined effect of fuel surface area, cover fraction and heterogeneity size was studied. Radiative transfer in heterogeneous maritime pines and dense shrub stands is shown to be very significantly affected by heterogeneity. On the contrary, lower effects are expected from Aleppo pine and light shrub fuel distributions. Further work will determine the appropriate resolution scale for vegetation description of each species and a way to take into account heterogeneity when no detailed information is available on fuel distribution. © 2006 Published by Elsevier B.V.