Relationships between building features and wildfire damage in California, USA and Pedrógão Grande, Portugal

Background Buildings in communities near wildlands, in the wildland–urban interface (WUI), can experience wildfire damage. Aims To quantitatively assess the relationship between building features and damage, a building wildfire resistance index is developed and validated with the 2013–2017 CAL FIRE (DINS) database from California, USA, and the 2017 Pedrógão Grande Fire Complex post-fire investigation from Portugal. Methods Three statistical dependence tests are compared to evaluate the relationship between selected building features and damage. The Wildfire Resistance Index (WRI), range: [–1, 1], is proposed and validated as a rating for building wildfire susceptibility. Key results The most correlated features to wildfire damage are the presence of vent screens and deck materials in California, and exterior walls material and deck materials in Portugal. For Portugal, as WRI increases by 50%, linear regression estimates a 48% decrease in proportion of highly damaged buildings, and a 42% increase in proportion of low damage buildings (R2 of 0.93 and 0.90, respectively). A total of 65% of California buildings with WRI = 1 were destroyed, compared to average 85% for WRI ≥−0.33. Conclusions The WRI quantifies the wildfire damage experienced by buildings in two diverse WUI regions. Implications The WRI could be used as an estimator of wildfire damage but it needs further development.