Modeling Wind Adjustment Factor for a prescribed burn plan. An application to Mediterranean stands in Southern Europe

Abstract

Wind speed, which is significantly affected by terrain and vegetation, is one of the most crucial factors in terms of fire spread. Fire simulators compute wind speed as open 10-m wind speed multiplied by the Wind Adjustment Factor (WAF). In forested sites, the sub-canopy wind speed plays a fundamental role in low intensity fire or prescribed burn, and therefore, in prescribed burn plan. This research aims to estimate a WAF model based on in-stand wind speed at 2-m above ground and forest characteristics. We use Chi-square Automatic Interaction Detection to classify WAF according to the most influential stand variables.Fifty-seven sampling sites were established for WAF training and testing. WAF ranged from 0.03 to 0.84, showing significant differences due to stand characteristics. Our findings showed that canopy cover is the variable with the greatest influence on WAF. On the one hand, the non-linear WAF model reached a coefficient of determination (R2) of 90 %. On the other hand, a decision tree performed four decision nodes based on canopy cover, stand height, and stand density. These approaches propose a novel method to the identification of WAF for fuel treatment and prescribed burning implementation, avoiding the errors that could be generated using fixed WAF for each fuel model. The proposed model can be used to simulate the effect of different canopy management alternatives, both fuel treatments and timber harvesting, in wind speed at 2-m height.