Relationship between the slope and some variables of fire behavior

Abstract

The topographic features influences fire regime and fire behavior jointly with the remaining environmental variables. The fire regime characteristics can vary due to fine scale topography and variation in stand history according to topographic features. The fire often influences severity with smaller areas of high severity on lower mesic slopes and larger areas on upper xeric slopes. Several researches confirm the severity of wildland fire. Topographic variables were relatively more important predictors of severe fire than either climate or weather variables. Predictability of severe fire was consistently lower during years with widespread fires, suggesting that local control exerted by topography may be overwhelmed by regional climatic controls when fires burn in dry conditions. This was an indoor study conducted at Forest Fire Laboratory, of Departamento de Engenharia Florestal, Universidade Federal de Viçosa (DEF/UFV), Minas Gerais State, Brazil. It was used a combustion table apparatus with a dispositive to simulate six slopes (0º, 5º, 15º, 25º, 35º and 45º). It was measured the flame length to correlate with the fire line intensity. Five replications were used for each slope, both in uphill as the downhill. The fuel bed was formed by a grass Melinis minutiflora Beauv. common in Brazilian grassland. The average values of dry fuel load for each slope were 0.561 kg, uniformly distributed on a platform area of 1.0 x 1.0 meter. The fire line intensity was calculated according to Byram (1969). The relative humidity mean in the downhill and uphill burn day was 48.8% and 57.8% respectively. The result showed that there was increases in the fire line intensity when compared downhill with the uphill slope from range 5 to 45 degrees. The increase was 2.7 times higher in the 45-degree slope compared with the lowest slope. This study will establish a factor for increasing the height of the flames and the fire intensity increased as the surface slope. In all replicates of downhill burning was observed a shorter length of the flames at the beginning and the end portion of plot while on uphill the flame length was shorter only on last plot portion. The flame length was a crescent relationship from 0 until 45 slope degree, represented by Y=1.1136+0.0675X-0.0012X2, with a R2 of 0.9362 for uphill and a polynomial representation of Y=1.0923X + 0.101X – 0.0046X2 - 5E-05X3 with a R2 of 0.8304 for downhill.