The effect of broadleaf forests in wildfire mitigation in the WUI – A simulation study

Abstract

The increasing occurrence of large wildfires in Southern European countries calls for the adoption of more effective measures of fire prevention, to protect people and infrastructures, namely in the Wildland-Urban Interface (WUI). Previous research suggests that broadleaf forests could mitigate the effects of these wildfires due to their lower flammability. However, few attempts have been made to investigate the possibility of using broadleaf-based green firebreaks to protect infrastructures, as an alternative to current less ecologically and economically sustainable fuel reduction techniques. Here, we assess the relevance of a broadleaves fuel model in reducing fire hazard in the WUI, by analyzing a set of six Industrial Zones (IZs) in Central Portugal, severely affected by wildfires during the catastrophic fire season of 2017. We developed alternative scenarios for the spatial simulation of fire behavior, using a factorial combination of weather conditions (standard and extreme), buffer around each IZ (distances of 100 m and 500 m) and land cover (current and broadleaves fuel model). The simulations were grounded on real-world data obtained from reconstructed fire front isochrones and fieldwork. Our results suggest that replacing the flammable vegetation present in the WUI with broadleaf forests could reduce fireline intensity by up to five times, even under extreme weather conditions. This reduction occurs subtly as the broadleaf cover interface is expanded from 100 m to 500 m. Our results show that fires that exceed the suppression capacity in pine and eucalypt forests (>4 m flame length) can be effectively suppressed in broadleaf forests under extreme fire weather (1.4 m flame length) and easily suppressed in broadleaf forests in standard weather (0.8 m flame length). Due to significant changes in land use and extreme weather events, future large wildfires could occur again in Portugal. In this regard, our results corroborate the urgent need to discuss forest management in the country, which has already proven to be insufficient to prevent fire disasters in the WUI.