Coastal forests catch fire

Fires are burning in coastal BC. This in itself is not a big deal, but the thick smoke in the air and local airtime devoted to the topic affirm its novelty. At least two fires in the (typically) wet Coastal Western Hemlock biogeoclimatic zone went from a few hundred hectares to several thousand in one afternoon and evening this past weekend; both fires were near the Whistler-Pemberton area, west and north of the Pemberton icecap glacier. Although the fires and their impact are not yet understood, the fire extents suggests that we may be experiencing a once-in-a century (or more) type of weather (and fire) event, the type of burning that defines a a 100 year (or 200, or 500 year) fire cycle. On the other hand, with our changing climate, this may become a more regular occurrence: our grand coastal temperate rainforests may now (or soon) be under the influence of something closer to a 50 year, or less, fire cycle.

But I really wanted to write about fuel typing and fire behaviour. Fire behaviour modelers have struggled with what to do with west coast forests for years. They don’t burn easily, but when they do, it’s a big event. Mind you, it’s not the spread rate that is notable but rather the smoke emissions, and sometimes the fire intensity – there’s just a lot of biomass there, and when it dries out and burns, it’s a lot of combustion. When modeling fire behaviour in these stands, I tend to use the C-5 FBP fuel type model (developed in red and white pine stands in Ontario); although C-5 is kind of a weak-kneed fuel type (suggesting relatively slow-spreading, low intensity fires), the model nonetheless tends to overpredict fire behaviour in coastal forests most of the time. It’s just kind of hard to get fires going underneath the thick canopy that holds moisture so well. The fire behaviour of the past weekend hasn’t changed my mind on this – I think the C-5 rate of spread model may still be reasonable (or overpredict somewhat in most cases). Rather, the fuel consumption estimates from the model (and consequently fire intensity) may be underpredicted. Let’s call it a hunch. I wonder if I can get any data on this.