From Cliff Mass’s Weather Blog
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There is an obvious contradiction regarding wildfires and climate in the western United States that few people talk about. The area of wildfires is low, although summers are warm and dry for most of the region.
This year has been one of the most benign wildfire years in a long time for the entire West Coast. The graph of California wildfire area since 1987 (see below) shows that the area burned in 2022 is quite low, similar to the situation 30 years ago.
Interestingly, this low-fire zone situation persisted despite the fact that the west coast states experienced warmer and drier weather than usual.
Consider the difference this year’s summer temperatures (June 1 to October 15) from normal (average 1990-2010)–see below. Warmer than usual for the entire coast! You would expect more fires right?
What about rainfall and drought? Well, people love watching the NOAA Drought Monitor, whose November 1 graphic shows a terrible drought in California and eastern Oregon, and a mild drought in the rest.
You would think this would encourage massive wildfires!
But it didn’t.
How is this possible?
It turns out that the occurrence of a forest fire is much more complicated than the simple relationship between wildfires, temperature, and rainfall described in some media and by some politicians.
Confirm this by plotting the average temperature, rainfall, and wildfire area in Washington from 2002 to this year (below).
2022 has the warmest summer (June to October) of the entire period so far.
And this summer is much drier than usual… the driest summer in 15 years!
However, the forest fire area is very low… again, how could this happen?
The relationship between wildfires and weather/climate is more complex than is often described
The link between climate and wildfires is much more nuanced than some have suggested. And that means the link between global warming and wildfires is not as clear-cut as is often claimed.
For example, strong winds are an essential ingredient for starting and spreading wildfires. And strong winter winds (such as those that propagated the recent Bolt Flame near Skykomish) are particularly important for wildfires west of topographic barriers in the region.
The absence of strong easterly winds this summer and fall has helped put out the fires this year. And recent research suggests that global warming could REDUCE such winds for the entire West Coast, reducing the likelihood of fires starting and spreading. You won’t hear about that in the Seattle Times.
Most West Coast fires are man-made, with poorly maintained electrical infrastructure being the primary cause. Significant efforts have recently been put in place to prune trees near power lines, harden electrical infrastructure, and shut down power lines when strong winds are forecast. This seems to be helping.
Warmer temperatures and drier conditions do not necessarily increase fire risk significantly. The West Coast has a Mediterranean climate with very dry summers. Even a normal summer allows surface fuels (such as grass and other light vegetation) to dry out enough to ignite. Once you cross the drought threshold, being a little drier makes a little difference.
And there are many other factors that affect wildfire areas beyond weather and climate. For example, poor forest management and fire suppression for 75 years created forests that led to a catastrophic fire. Invasive combustible grasses have increased fire threats, as well as increased human ignitability. The new directives “let it burn” are increasing the fire. On the other hand, once there is a fire, the area is less likely to burn for a while.
In short, the relationship of a bushfire area to weather or climate is complicated with many other important – if not more important than… factors other than climate.
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