An expert system to quantify wildfire hazards in gardens and create effective defensible space

Wildfires are causing increased house loss worldwide, especially at the wildland-urban interface. Despite the existing plethora of guidelines to help creating defensible space in a garden and protect houses from wildfire, quantifying risk remains a research frontier. We designed an assessment method based on a recent global review of defensible space guidelines and identified hazards based on fuel type, amount, and spatial arrangement. We trialled the assessment in 32 gardens located in southern Tasmania (Australia). We combined survey data using an expert system enabling calculation of hazard scores that accounts for the interaction between fuel characteristics and used sensitivity analysis to rank individual hazards based on their impact on hazard score. Gardens included a high number of plant taxa (N = 374), 72 % of which were exotic to Australia. The most common hazards were represented by material objects close to the house, as well as plant cover, garden vertical structure, and flammability of plants across the whole defensible space. Most gardens achieved an overall ‘Moderate’ (N = 15) or ‘High’ (N = 13) hazard score, with only two classified as ‘Low’ and one as ‘Very High’. Sensitivity analysis identified vegetation characteristics – cover, location, and watering status – as well as the presence of fire-protective elements as the individual variables with the highest impact on overall hazard score. The proposed method quantifies fire hazards within gardens, provides flexible solutions to support guideline implementation, and facilitates comparisons across different geographic settings.