Wildfire Risk Increases for Western US Due to Wet and Cold Conditions – Do You Accept It?

news7g04/23/2023

4 3 minutes read

Wildfire Risk Increases for Western US Due to Wet and Cold Conditions – Do You Accept It?

There is a high probability of wildfires in the western United States next summer and early fall, but not due to the hot and dry weather.

In fact, the opposite. A cool, wet winter has created an increased wildfire threat by creating large amounts of combustible grass.

A threat stretched from eastern Washington to southern California.

East Washington Near Thorp, WA, July 2022

When most people think of wildfires, they usually refer to wildfires. However, grass fires are just as important in the West, if not more so. Furthermore, burning grass plays an important role in many wildfires.

Many of the most damaging fires in the western United States have a large contribution of grass. For example, the town of Malden in eastern Washington, which was destroyed in September 2020, and the 2018 Camp Fire around Paradise, CA.

The distribution of seasonal grasses in the West is shown below (indicated in green). There are A LOT of grasslands throughout eastern WA and OR, as well as central and southern California. And many forest areas have understory consisting of grass and other seasonal vegetation.

The American West has a Mediterranean climate, with rainfall in winters and dry summers (yes, this includes Washington State). Precipitation during winter encourages seasonal grass growth followed by a warm/dry period in summer, resulting in significant amounts of combustible fuel in midsummer. All that is needed is a source of ignition and strong winds, leading to a fast-spreading fire.

Studies show that rainfall is most important around November (supporting early germination and growth) and in March/April (providing moisture as the sun strengthens encouraging rapid plant growth) ).

Interestingly, western grasslands and grasslands have become much more flammable over time, as non-native, flammable grasses like cheatgrass have spread throughout the West. This is NOT due to global warming. And today there are more sources of ignition, including a massive increase in electrical infrastructure and population at the urban/wildland interface.

To get a visual idea of how important grass fires are, here’s a map of historic fire sites for central CA. Lots of big fires far away from the mountains. Importantly, broad grass near and in forested slopes can play a major role in initiating and spreading wildfires.

Widespread wildfires have also been found in grassland areas around eastern Washington State (see below).

Situation this year

The percentage of normal precipitation for the current water year (October 1 to present) is shown below. Most of California is wetter than usual as well as southeastern Oregon and the eastern slopes of the Cascades. Surprised that the eastern slopes of the Cascade are wet? Blame the easterly, offshore currents for making the rest of the region arid!

Crucially, higher-than-normal rainfall continued throughout this pivotal month in California, Oregon and yes, the slopes east of the Cascade.

All this moisture has encouraged the overgrown grassland growth around the West.

Would you like to see some proof?

Here are two NASA MODIS satellite images for southern California: the first is from today and the second is from two years ago (2022), also on April 21.

Look closer. Much greener today. When that thing dries….because it WILL dry…. there is a potential risk.

But let’s be more quantitative about the wildfire threat.

A great USDA website called Fuelcast.net uses rainfall and other data, processed with machine learning, to predict how much dead fuel (mainly dead grass) will be later this summer ( see below). As noted by grassland/range expert Dr. Matt Reeves, when dead fuels stand up to about 800 pounds per acre, the threat of wildfires is enormous.

As is evident below, much of eastern Washington, eastern Oregon, and especially California will reach that level.

Bottom line: there is a significant grassland/pastoral bushfire threat this summer after the dry West, as it always does.

There is a lot of talk in the media and others that wildfires in the West are mainly the result of heating and drying caused by global warming. The truth is perhaps a little more nuanced and complex. Cool and wet winters and early spring can significantly increase wildfire threats.

___________________-

The program and information about the Northwest Weather Conference is online. If you want to attend, you must register (on the website). Some speaking positions remain open to those interested in presenting.