Updated 16 October 2020
Like so many topics in the public eye, wildfire is very complex. For anything I state, it’s not hard to find exceptions. Every biome, every climate, every terrain has different wildfire regimes.
As a result, I feel great disappointment when I see overly simplified comments in the media, in social media, and from my friends and family. This desire to over-simplify makes a lot of sense – we don’t all have time to dig deep, and it’s simply easier to accept a simple explanation that puts our mind at ease. But this is where we must actively fight our inclinations about those exceptions. Don’t dismiss them, and don’t embrace them as reality just to support a pre-existing view. My own personal assumptions about wildfire have dramatically changed in the last year and even in the last month as I’ve embarked on a crash course in wildfire ecology.
Let’s dive in.
It’s not just a California problem.
Oregon has had one of its worst fire seasons in history. Also, Oregon has shown a steadily increasing trendline (note, the citation doesn’t show 2020, which will likely rival 2012 as the all time worst). Arizona’s 5 largest fires of all time have occurred in the 2000’s. And 8 of the top 10. The two that didn’t occur in the 2000’s were in the 1990’s. Total acres burned annually in the US as a whole has steadily (and rapidly) increased. Colorado, Washington, British Columbia, and other states and provinces have also seen an uptick in recent years (last couple decades). Montana and Idaho had a 1.3 million acre fire in 2017. Yes, eastern fires show less consistency, but more on that later.
Not all wildfires are in forests.
Taking California 2020 stats, about 38% of land area burned is forest. That means 62% was in other habitats – shrubland, oak savanna, grassland, etc. Many structures burned due to shrub/scrub fires. This brings us to…
Every biome/climate combination has a unique natural fire regime.
Scrubland, based on historical records (ash records, charcoal records, tree rings, and other forensic methods) in California historically (pre European civilization) burn every 30-200 years. The Sierra Nevada foothills and mountains (mixed oak woodland transitioning to coniferous) had a pre-settlement return interval of 10-30 years. Also note one important difference: these historical fires rarely burned the forest to the ground. They were fires primarily of the underbrush – generally quick moving and low intensity.
Also, be careful when comparing to other regions in the USA because climate, terrain, vegetation types, and quantities of unfragmented wildlands also vary dramatically. Each case is different – whether it be Florida or Maine or Texas. Each scenario has to be considered individually in the context of the aforementioned variables.
I have not researched each of these, but did find that climate models indicate that Texas and Florida won’t see the generally steady upward trend in wildfire seen in Arizona, California, and west, but instead will see occasional unprecedented devastating fires on infrequent intervals.
The deadly Camp Fire that destroyed the town of Paradise largely burned over an area that burned just 10 years prior.
In fact, the area has had multiple fires since 1998. That leads us to…
“Raking, thinning, and fuel removal” is not a silver bullet.
In fact, it is more like a BB than a bullet. The Camp Fire is illustrative of the new wildfire problem we have. As stated above, normal fire return in the Sierra is 10-30 years, so the Camp Fire was not abnormal in that respect. But why did it explode so quickly? Why did burn so quickly? Obviously, understory fuel load is not the issue here since much of the area burned recently, and much of it was replanted/reforested for harvesting.
Of course, there are some specific cases where prescribed burns or thinning may reduce risk, but this is the exception, not the rule. It is true that decades of aggressive fire suppression have had negative impacts, including, in some cases, excessive fuel build-up. This also makes for an easy explanation, though also a lazy explanation. As the Camp Fire and numerous other examples show, this is far from the only factor,.
The myth that thinning solves everything ties back to the incentives of money and resource extraction, and not science. See potential explanations in the discussions on PG&E and poor reforestation practices below.
Arid western climates are more at risk from warming temperatures.
It’s a well known fact that evaporation increases with temperature increase, assuming constant humidity. Plants also release more water with higher temperature (transpiration). The two together is called “evapotranspiration”. A large oak tree can transpire 200 gallons of water a day in hot and dry weather, or 25 gallons in cool and cloudy weather. Consider those numbers in the context of millions of trees and multi-day all-time record heat. Measured temperature increases in the last 20 years have equated to an additional net deficit of up to 0.75 inches of water each peak summer month across California each year, with some estimates showing a 3 inch annual deficit simply from warming air. This isn’t considering actual precipitation, which has also been on a decline.
The biggest climate change impacts in the west are longer fire seasons, creating a longer risk exposure. Washington state’s fire season length has roughly doubled since 1970. California regularly sees fire season extending into late October and November – something rarely seen a few decades ago. In fact, 2020 may be the third year in a row that the SF Bay area has ZERO rain in October.
Wind-driven embers are what make fires spread faster.
We might envision a wall of fire advancing when we think of wildfires, but in reality, embers are blown, sometimes up to 2 miles in front of the fire wall, igniting new blazes. Wind and fires are a terrible combination, and this relates to the “human caused fires” discussed further below.
Back to the Camp Fire, embers advancing in front of the fire were the primary issue that made this fire so deadly and advance so quickly. You might think that wind driven fires are “natural”, and to a small extent, they are. However, these fires are orders of magnitude more common due to the human impact, which we’ll talk about later.
Reforested habitats (including “tree farms”) make wildfires worse.
Reforested areas have been shown to burn as rapidly or more rapidly than natural mixed vegetation with understory (much of the Camp Fire area was previously re-planted as a tree farm). This is partly because the vegetation creates wind breaks, and partly because the vegetation catches embers. These reforested areas don’t have the natural gaps and clumps, either, that create natural fire delays. They are optimized for yield for one or two species – just like farm fields. Of course, monocultures are bad for biodiversity (and also bad for long term forest health, but that is a story for another day), but in this case, it’s worse because the method makes fires worse.
In the shrublands, invasive grasses introduced 200+ years ago have taken over, and are ever expanding due to both fire and grazing. Grazers, like cattle, eat the native vegetation too (i.e. oaks, manzanitas, sage, etc), and allow the grasses with their shorter life cycles to spread to new areas. These grasses burn quickly and easily.
Human Caused Fires Makes Everything Worse
Now, consider that the narrative in the mainstream has been “log more, thin more, remove fuel” (see above). So it might seem counterintuitive to say that more human started fires is bad. After all, these fires are burning fuel, which should make the land safer. But as discussed above, fuel removal is far from a silver bullet, and worse, still, human start fires at the absolute worst times – times when natural fires would be rare.
Let’s step back and consider – what starts fires naturally? Lightning. Normally, lightning doesn’t happen on days where it is 100 degrees with exceptionally dry dewpoints of 40 degrees (especially in the coastal ranges of the west, but yes, this does happen vary rarely in the Sierra Nevada range). But human fires do start in these conditions, regardless of the location, and this allows them to spread more rapidly and become hotter and more devastating. These hot, dry days are usually associated with brisk down-sloping winds, too.
And let’s consider the devastating PG&E (electricity utility company) fires in California. Their power transmission lines were implicated in several of the most severe fires of the mid/late 2010’s, and upwards of 1000 fires total. Making this especially bad, these fires occurred during uniquely Californian wind events. The wind event that triggered the transmission line failures that sparked the fires is also what caused these fires to advance so quickly. Again, a natural wildfire regime rarely has this issue, because these wind events are NOT associated with lightning.
Of course, you might be saying that the August 2020 California wildfires were largely caused by lightning. This is true, and that was a once every 50 or 100 year event (some say even longer!) Maybe related to climate change, maybe not, we just can’t say. I call it bad luck.
But even when we eliminate the lightning fires of 2020, we see the same long-term trend of human-initiated fires during the worst fire weather days. In fact, nearly 85% of wildfires in the USA are started by humans, whether it be utilities, hunters, campers, kids playing, or even a 23,000 acre blaze caused by a gender reveal party.
Models of Climate Change Impact Match Observation.
Yes, climate change is exceedingly complicated. All the models show some of the complexity – some areas will get wetter, some drier. Some hotter, and yes, a sparse few places will even get colder. Hurricanes, droughts, and other extreme events will be more common over long periods of time. Much of the western USA is projected to get hotter and drier with longer fire seasons, so that certainly means more explosive fires.
Some mid-latitude areas will get more tropical rains. But that also means that while fires might reduce in those areas, in the rare years where tropical impacts are down and drought occurs, fires will be worse. This is a case where we really have to rely on the models and the trends, and not over-react to specific events. So far, both the models and trends match.
Climate Is Not Linear.
While many of our trends are scarily consistent, worsening each year, regional climate is not as linear. Things like El Nino/La Nina, the Pacific Decadal Oscillation, the Atlantic Multidecadal Oscillation, and other ocean-driven long term patterns will serve to amplify – or blunt – the impacts at times. These trends are generally understood and somewhat predictable, and should be considered in the context of their amplifications or cancelling effects. Taking a few examples, western wildfires correlate strongly with the PDO. Texas wildfires correlate with La Nina.
Fires are also worse because the human impact is worse.
There are more communities at the wildland/urban interface (WUI) than ever before. Areas that used to be considered lower risk are now moderate risk because of the speed and intensity of current generation fires. And we make all of it worse by having misaligned incentives and not implementing simple risk mitigations.
On the incentives side of the equation most towns and cities are driven to expand there tax base. There are many underlying reasons for this – economic expansion, increased services, increased power, etc. When combined with wealthy land developers who hold a lot of sway, it is easy to see why more developments are placed in the WUI. Currently, the long term risks of fire or other natural disasters are not adequately incorporated to this development-centric equation.
Almost all focus is on “defensible space” and non-flammable roofs. This is an important start for a fire safe property, but defensible space doesn’t protect against blowing embers from a mile away. A metal roof helps. removing flammable objects from your defensible space helps. But what about the pile of leaves and pine needles in your gutter? Or at the corner of your house? Or the soffit vent that allows embers to enter the attic? Two things solve these problems – an ability to close off attic and crawl space vents; and exterior sprinkler systems. Many communities across the world use exterior sprinklers, but it is still rare in the USA. But there are many stories of single buildings escaping unscathed because of a $1000 investment in external sprinklers.
What is the bottom line?
- Frequent fire is normal. Some biomes are seeing too much fire, while others are still seeing about the same frequency.
- The intensity and size of our current fires is not normal, across nearly every biome.
- Intensity, size, and frequency largely correlate with the human-triggered nature of the fires. Natural triggers rarely correspond with high wind events or peak heat days. We need to reduce human causes.
- Fuel build-up is not the primary issue, and in fact, rarely an issue in the California fire cases, as well as many others in the west.
- We need smarter land rehabilitation. Reforestation needs to be naturalized, and include an understory. Active restoration, at-scale, of scrubland is needed.
- We need smarter solutions at the wildland/urban interface. Exterior sprinklers on structures can be implemented to save entire communities.
- We need to start taking climate change seriously, since it adds increasing pressure to much of the USA, even if not all areas see the same linear increase.
- These improvements will take years, if not decades, to make a noticeable difference. We need to be in it for the long haul.