Prescribed vs. Wildfire Smoke Emissions Tradeoffs Analysis

Smoke from recent wildfire seasons has greatly impacted communities across the Pacific Northwest.  Climate change is leading to longer, hotter and drier summers with a marked increase in area burned by wildfires and regional smoke impacts. Although much of the media attention has been on the number and size of wildfires, the quantity and type of wildland fuels that are available to burn have important implications for how severely wildfires burn and their smoke impacts to communities. 

Mitigating Smoke with Proactive Management

Prescribed burning is increasingly recognized as one of the best strategies for reducing wildfire impacts, including the particulate matter and greenhouse gas emissions released by wildfires. Specifically, prescribed burns target accumulated dead wood, tree needles, shrubs and grasses. For a time following prescribed burns (generally 10-15 years), the reduction of wildland fuels can mitigate wildfires by making them less intense and reducing the duration and amount of wildfire smoke. 

Tradeoffs between prescribed burning programs and wildfires were recently highlighted in a  2022 report  by the American Lung Association. 

Fine particulate matter that is < 2.5 microns in size (PM 2.5), in particular, is  linked  to serious human health impacts from wildfire emissions. However, even though prescribed fires are carefully planned to minimize smoke impacts, they are increasingly difficult to implement due to  human health concerns .

In this project, we made use of an existing, large-scale dataset to evaluate prescribed fire and wildfire emissions scenarios within the interior Pacific Northwest. The Interior Columbia River Ecosystem Management Project evaluated how 20 ^th  century fire suppression and other land management practices had led to pronounced expansion of forest cover and fire hazard, particularly within historically fire prone landscapes of eastern Oregon and Washington. An early and preliminary  analysis  was conducted to model how prescribed fire and wildfires would differ in both their fire behavior and smoke production, but recent updates in tools, datasets and mapping technologies offer an opportunity to perform a more robust tradeoffs analysis than was previously possible.

We evaluated how smoke tradeoffs between continued summer wildfires versus expanding prescribed burning programs differ. 

Modeled scenarios can be used to identify strategies that greatly expand spring and fall prescribed burning and assess how investment in prescribed burning could eventually reduce summer wildfire smoke in the Pacific Northwest. 

Our project study area includes the entire Interior Columbia River Basin and makes use of aerial photo interpretation of a 10 percent subsample of watersheds using  source  imagery from the early and late 1900s. These “historical” and “current” landscapes were delineated into patches of young, maturing and old forests along with nonforest vegetation including grasslands and shrublands. We developed a repeatable, scripted crosswalk approach to assign realistic fuel characteristics based on forest and nonforest vegetation type and age.

Once we completed the crosswalk from interpreted patches within historical and current landscapes to realistic fuel characteristics, we made use of two decision support tools to compare model predictions of fire behavior and smoke production. 

 The Fuel Characteristics Classification System  (FCCS) summarizes the live and dead biomass of vegetation (often termed “fuel loading” in fire science), categorized in layers from organic soils (often called duff) to litter, downed wood, and understory vegetation, to forest canopy fuels. Wildland fuel characteristics are incredibly diverse and can range from very low loadings (e.g., dry grasslands) that generate very little smoke to very high loadings (e.g., mixed conifer forests that have been long unburned) that generate massive amounts of smoke, particularly during crown fires in which tree crowns burn along with understory fuels. 

Consume uses calculated fuel loadings from FCCS to predict fuel consumption and smoke emissions under user-specified  scenarios . 

Our first analysis focused on wildland fire management scenarios using the current subwatersheds in the Interior Columbia River Basin. Future analyses will include comparisons with historical landscapes as well. 

The following scenarios were used to evaluate if and how treatments over time may reduce smoke impacts to communities. After over 100 years of no fire in many forests of eastern Washington, the first wildfire event (scenario #1)  is expected to produce the most smoke. However, following a prescribed burn, smoke impacts of the second wildfire and second prescribed burn are reduced.

Below are two selected subwatersheds that are shown in more detail:

The tables below show the total PM2.5 for each scenario for all watersheds in the sample