Contributed by Ralph Bullis, P. Geol., FGC © Sept. 2017
With such a bad wildfire season in BC and with so much disruption in the province, I suppose it’s inevitable that someone (Al Gore? CBC? The Weather Channel?) would step up and state categorically that this is all caused by humans using fossil fuels.
However, if you look up the BC government and federal government statistics on BC wildfires and plot out the past 40 years – since 1977 – and what you find is somewhat surprising. First of all, there has been a steady decrease in the number of fires over that period with the average being just over 2,100 per year. This year, up to early September we’ve had about 1,230. Yet, the number of hectares burnt is huge – almost 12,000 square km – more than the previous worst in 1958 (with about 8,550 sq. km.).
The second thing that surprised me in the data is that up until about 2002, the average number of sq. km. burnt per year was about 320 and the trend was flat (with an anomalous spike in 1982 with about 2,800 sq. km. burnt). But since 2002 we have seen a significant increase in the areas burnt – in fact the average from 2003 to 2016 is about 1,550 sq. km. or about 5 times the average up to 2002.
So what’s going on? How can the number of fires annually be steadily going down yet the amount forest being burnt increasing and the increase in burnt areas beginning about 2002?
Well, I talked this over with some friends and the suggestion arose that perhaps the insect infestations might play a role.
So, I retrieved the insect infestation data and when I plotted the pine beetle infestation numbers, it turns out that there was a rapid increase in the number of hectares infested starting in about 2000. As you can see from the attached plot, the number of hectares under pine beetle infestation climbs rapidly from less than 200,000 ha in 1999 to over 10 million ha in 2007. The good news in all of this is that the beetle infestation since then has been rapidly dying off, down to just over 300,000 ha in 2015.
So, just at the same time period when extensive areas of forest were dead or dying due to pine beetles we see an anomalous uptick in forest fire extents.
Now, the coincidence of larger fires and extensive forest kills due to pine beetles may be just that – coincidence – and there may not be a correlation. But, if it comes to a choice of blaming the extensive forest burns on climate change or on those huge expanses of highly combustible dead forest due to pine beetle infestations, I know what the scientist in me would select.