Empirical models of initial attack fire behaviour reduction by skimmer airtankers in Ontario’s boreal forest

Background Airtankers are used during wildfire initial attack suppression to reduce fire behaviour and enable ground suppression, yet there is little empirical evidence on how suppression from airtankers reduces fire behaviour. Aims To quantify the relationship between airtanker suppression effort (i.e. number of water drops) and fire behaviour reduction for two commonly used skimmer airtankers (Canadair CL-415 and DHC-6 Twin Otter) in Ontario’s boreal forest. Methods Probabilistic models were developed to estimate the likelihood that airtanker suppression reduces fire behaviour to a smouldering state as a function of suppression effort using 17 years of operational observations recorded by air attack officers. Key results The probability of fire behaviour reduction increased with greater suppression effort. CL-415 airtankers required fewer drops than Twin Otters to achieve similar reductions, with differences most pronounced at more severe fire behaviour levels. Suppression from CL-415 airtankers showed that aerial suppression can be effective when active crowning is observed. Conclusions Aerial suppression meaningfully reduces fire behaviour across a range of conditions but often requires greater suppression effort than predicted by theoretical models. Implications Results provide empirically derived suppression effectiveness models that can support airtanker deployment decisions, dispatch optimisation and suppression system simulation under current and future fire regimes.