Using observed fires to study changes in fire season timing across Ontario, Canada

Background A lengthening fire season could lead to more fires and more intense fires. This can pose challenges to fire management logistics and budgets when making staffing decisions such as seasonal contracting of crews and equipment. Aims We investigate where and at what rate the length and timing of the wildfire season is changing across Ontario, Canada. Methods The province is partitioned into grid cells. A new algorithm that uses observed wildfires is developed to identify the timing of the start and end of each year’s fire season. These are analyzed to quantify trends in the fire season over time and space. Key results Fire season length is increasing across much of northern Ontario, with earlier human-caused fire start dates and later lightning-caused fire end dates. Median rates of increase are about 0.5 days/year in the northwest and 0.25 days/year in the northeast. Conclusions Our findings corroborate past studies showing that Ontario’s fire season is changing but provide more spatial insight as to where. Implications Should such trends continue, this could impact the province’s long-term level of protection process, such as the definition of its official fire season start and end dates and seasonal and long-term resourcing decisions.