Wildfires are known to occur on every continent except Antarctica, and both fossil and historical records indicate that these disasters have been a threat to human lives and shelters since our earliest days. Wildfires are particularly common in areas with long periods of hot and dry weather, but also with enough vegetative growth to provide fuel. Since global warming is predicted to increase temperatures and alter precipitation patterns, many worry that ever more human settlements will be threatened by wildfires in the future. Thus, it seems a good time to improve our understanding of the factors associated with wildfire damage, and to use this information to develop management techniques that reduce the risk of damage.
This was the aim of collaborators from Australia and the US who recently quantified which landscaping and management practices were associated with the loss of houses during a trio of Australian wildfires that occurred in 2009. They were interested in focusing on home loss not just because of the obvious value of homes, but, more importantly, because the majority of wildfire-related human deaths occur in domestic buildings--which residents often stay to defend, attempt to take shelter in, or evacuate from too late. In the Kilmore East, Murrindindi, and Churchill fires examined in the current study, for instance, 69% of the 170 documented fatalities occurred in homes.
Researchers already know that the behavior of wildfires is predominantly affected by three variables: terrain, weather, and fuel. Characteristics associated with each of these three categories were cataloged for a total of 499 houses--some of which escaped damage in the recent Australian wildfires, and others of which were not so lucky. Terrain was not found to have any effect on house damage, and the patterns associated with weather were highly predictable: more homes were lost when temperature and wind speed were high, and humidity was low. The real variable of interest was "fuel," since it is not only quite variable among homes, but is also often the easiest for humans to control.
The researchers found that houses were most at risk when they had buildings and vegetation--particularly native species, rather than exotics--within 40 m; when prescribed forest burning efforts had taken place at some distance, rather than nearby; and when houses had less private land separating them from public land, parks, or forests. These patterns are likely a result of the fact that most houses catch on fire after being exposed to embers and radiant heat generated by the burning of nearby fuel. Thus, it isn't surprising to find that modifying or removing potential fuel could "substantially reduce house loss." In this case, "substantial" could, in some cases, mean nearly halving the rate of destruction. Specifically, the scientists estimated that decreasing native vegetation within 40 m of houses could reduce house loss by 43%; removing all trees and shrubs within 100 m could reduce loss by 26%; and conducting prescribed burning efforts within 0.5 km of homes, instead of the current average of 8.5 km, could save 15% of properties.
On the whole, these results indicate that the most important goal is to increase "'defensible space,' or the area around houses in which suppression is most likely to be successful." While it's up to private property owners to follow up on many of these suggestions, government managers may also need to think about modifying their current prescribed burning techniques if they want them to benefit communities as well as wildlife. Specifically, one major finding of the current study was that the benefits of the burnings appear to be short-lived, indicating that they should be conducted more often, as well as closer to at-risk neighborhoods.
The authors caution that their results may not be applicable across all fire-prone regions; additional work should be done in order to investigate patterns in locations with different weather and floral communities. Furthermore, although the techniques reported here may be optimal for maximizing survival probabilities of homes exposed to wildfire, they may be costly or difficult to achieve--and they may have unintended negative side effects. Finally, the researchers suggest that it is worthwhile to investigate alternative management methods that could mitigate the important impact of weather; these include architectural solutions, creation of alternative shelters, and innovative suppression efforts.
Gibbons, P., van Bommel, L., Gill, A.M., Cary, G.J., Driscoll, D.A., Bradstock, R.A., Knight, Moritz, M.A., Stephens, S.L., and Lindenmayer, D.B. 2012. Land management practices associated with house loss in wildfires. PLoS ONE 7(1):e29212.
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