Is global warming behind the recent smoky period in Western Washington? – Is it good?

Imagine if you were a journalist assigned to write a story about the potential link between global warming and wildfires in the west. You will definitely want to ask the following questions:

first. Has the burned area west of the Cascade peak increasing over time? If global warming is to blame, one would expect more westward wildfire trends over the past few decades when warming was greatest.

2. Have meteorological factors associated with fires in the west tend to increase over the past decades? Furthermore, do climate model projections indicate increases over time in these key parameters?

In the case of a fire in the west, the main parameter is a strong easterly (from the east) wind. All major fires in the west are associated with such winds. Another (minor) factor is late summer and dry fall, the season for virtually all fires in the west.

The Yacolt Fire of 1902 was the largest western fire in 120 years. Trusted journalists and climate activists should ask and answer these questions. And it turns out that The best answers to these questions clearly indicate that global warming does not and will not increase such western wildfire events.

Let’s look at the truth.

Is there a wildfire trend in the west?

Below is a diagram of the burned site west of the Cascade Peak in Washington. There were BIG fires in the early 20th century (Yacolt, 1902; Dole Valley, 1929). After that, almost nothing until the 1951 Olympic Peninsula Flame was much smaller. Then another fire “drought” to another small fire during the Olympics (Paradise fire 2015), which followed this year’s modest fires.

Do you see evidence of a trend toward more fires west in Washington? I do not. And that alone should be enough to dampen any claims of greenhouse warming fueling the fires in the west.

Essential meteorological requirements for Westside fires

The western forests are generally not prone to large fires. The reason is obvious: these are relatively humid environments, with heavy rainfall totals on windward slopes during the cool season. They are characterized by a moist, green canopy.

The period from June to September sees little rain in a normal year and slow drying of the surface in summer, as well as melting of snow and ice at mid and higher altitudes. During the summer, there is usually an inshore current from the Pacific Ocean that keeps the temperature moderate and the air relatively humid. An inhospitable environment for western fire.

During most of the summer and fall, the air that permeates western Washington is cool and humid.

As long as the flow is in the west (from the west) there is very little chance of a large wildfire in the west. So, the NEED ingredient for fires in the west is a STRONG winter wind.

Repeat that statement 3 times. That’s the important thing.

The Easter monsoons encourage wildfires in the West in a number of ways. First, it replaces cool, moist oceanic air with very dry, warm air east of the Cascades. Relative humidity can be reduced from 50-80% to less than 10%. Dry conditions are great for fire, helping to quickly dry surface fuels – this makes them much more flammable.

Second, as the winter runoff descends the western slopes of the Cascades, it is warmed by compression, making the humidity even lower. The very warm and dry air over the mountain slopes enhances the possibility of fire.

Third, strong winds can supply more oxygen to the fire (which they need) and can blow hot embers before the fire, helping them spread faster.

Fourth, strong winter winds can START fires, such as knocking down power lines or pushing branches onto power lines.

I have a National Science Foundation project to look at the western wildfires in Washington and northern Oregon and I (and my students) have studied EVERY major fire in the west. EVERYONE OF THEM is associated with strong winter winds.

Given these important insights, what will global warming do to the strong winter winds in our region?

The answer: global warming (aka climate change) will WEEK the winter winds, working AGAINST more fires.

To reach this conclusion, we applied a set of many high-resolution, regional climate simulations. As illustrated in the figure below (from a peer-reviewed paper), an increase in greenhouse gases (such as CO2) leads to weaker winter winds (in this case near the top of Central Falls). Washington).

Number of days with strong winter winds from 1970 to 2100, based on high-resolution climate model projections

The reduction of strong winter winds coupled with global warming makes complete sense physically.

Global warming favorably warms the interior of the continent over the slow-warming coastal region. Warming contributes to a decrease in preferential pressure on the interior. Strong winter currents are associated with higher pressures inland relative to the coast, and therefore, preferential warming inland will DRIVE winter runoff.

So the best science, from modeling to physical reasoning, shows that wildfires that cause runoff from the East will be WEEKLY under conditions of climate change. Contrast with recommendations on Seattle Times and elsewhere.

Is autumn drier?

Although winter winds are an important requirement for wildfires in the west, dry conditions are clearly helpful. The Westside bushfires have occurred during periods of normal rainfall when winter runoff is strong and sustained, but previous dry conditions have shortened the time it takes to dry the fuel to the surface. This year has been extremely dry – the driest summer/early fall – and this allowed last week’s strong winter winds to rapidly intensify pre-existing fires and start new ones. .

So let’s get to the basic question: will late summer/early fall rainfall decrease on the western slopes of the Cascades and in western Washington in general?

The answer is no.

This is a graph of August-October precipitation over the last century for the western slopes of the Cascades (and the eastern slopes of the Olympics) taken from the NOAA Climate Division dataset. There is no long drying process – if anything the rainfall increases a bit. Plotting other areas or individual stations west of Washington produces a similar uptrend.

What do climate models predict for the future of fall rainfall as the Earth warms? As shown below, precipitation INCREASE.

Key point

Contrary to claims by the Seattle Times and some types of activists, there is no reason to expect an increase in the size or frequency of westward wildfires in the future. No increasing trend was observed in the wildfire area west of the Cascade Peak. Global warming will weaken the strong winter runoff, a key meteorological factor associated with autumnal wildfires in the west. Furthermore, there is no evidence that autumn rainfall decreases in the region, and climate models suggest that such rainfall will in fact increase.

____________

To listen to my podcast, use the link below or access it through your favorite podcast service.

Some of the main podcast hosts: