Detecting Temporal Changes in the Seasonality of Forest Fire Risk in Canada

Lightning-caused fires account for approximately 45% of the ignitions and 80% of the area burned by wildfires in Canada.  How climate change may be impacting the risk of lightning-caused forest fire ignitions is therefore of significant concern.  Whether or not the peak ignition risk is increasing over time and/or the “fire season” is becoming longer each year are of particular interest.   We developed a flexible suite of statistical models that can be used to investigate these questions and we applied them to fire ignition data for the years 1961-2003 in the province of Alberta and 1963-2009 in the province of Ontario.  The fitted models suggest changes in fire ignition risk patterns in both provinces.  In Alberta, the fire season appears to be both starting earlier and ending later.  In Ontario, no significant changes in the timing or the length of the fire season were identified.  However, in a portion of northwestern Ontario in which most fires are actively suppressed, a shift towards an increased risk of fires during the fire season was observed.  We will also discuss what length of data is required to be confident when results suggest significant trends.