Overwinter holdover fires



Holdover fires are not a new phenomenon, and the BC Wildfire Service has experience responding to them.  

What are overwinter holdover fires?

In some fuel types, existing wildfires can move underground and slumber throughout the winter months and resurface the following spring. These fires – also known as overwinter fires – burn deep underground into the organic matter on the forest floor.  

When snow begins to fall and the ground freezes, these fires become dormant, meaning their heat signatures become less easily detectable. This makes it difficult for wildfire crews to locate and action hot spots until they flare up. Through the winter, visible heat signatures and visible fire activity are infrequent and difficult to detect due to overcast, foggy and/or snowy conditions. 

Holdover fire activity is typically limited to unburnt fuel within the existing fire perimeter from the previous year. As local weather conditions warm and dry in the spring, the heat smoldering underground has the potential to ignite these previously unburnt surface fuels within the perimeter and may result in visible smoke. If conditions continue to warm and dry, any additional unburnt fuel in the area may ignite. This could increase the fire activity of the resurfaced holdover fire and may result in visible flames and smoke.  

Gusting surface winds have the potential to carry burning embers, or firebrands, from the resurfaced holdover fire beyond the main fire perimeter and result in spot fires. This is how holdover fires have the potential to become large, active wildfires again in the spring. 

Why are we seeing more?

Across western Canada, including B.C., Alberta, Yukon and the Northwest Territories, continued extreme drought and warm, dry weather conditions have fuelled significant fire behaviour. B.C. has been experiencing unprecedented drought for more than two years, particularly in the northeast where water basins have received minimal rain or snow for a year.  

Due to this ongoing drought, record low snowpack, and the extensive area burned during the 2023 wildfire season, many holdover fires were not extinguished. This allowed them to persist in the organic material under the frozen ground and snow cover through the winter. Regions with boreal ecosystems, characterized by deep peatlands such as those in the northeast, provide an ideal environment under drought conditions for fires to holdover through the winter burning underground. This is demonstrated in the image below.

G. Rein, Smouldering Fires and Natural Fuels, Chapter 2 in: Fire Phenomena in the Earth System – An Interdisciplinary Approach to Fire Science. 

Fire seasons resulting large areas burned and followed by dry overwinter and spring conditions will result in more holdover fires, as it is impossible to suppress thousands of kilometres of fire perimeter. 

How are overwinter holdover fires managed?

The BC Wildfire Service has moved to year-round (rather than seasonal) operations to strengthen our planning, prevention and preparedness, as well as our response and recovery efforts. 

Fires that remain active into the winter are classified as Under Control, based on a combination of suppression activities and local weather conditions. This status indicates that the wildfire is not expected to spread outside of pre-established boundaries. We monitor these fires for smoke and heat signatures, which could indicate new growth.  

Over the winter, the BC Wildfire Service manages holdover fires by establishing fire guards where needed to protect people and infrastructure, as well as actively monitoring holdover fires and reporting on these fires publicly. When activity resurfaces and further wildfire response is needed, response tactics and priorities are established as conditions allow. 

Monitoring through the winter months

The BC Wildfire Service monitors holdover fires through the winter to detect hotspots within the perimeter. A combination of satellite and aircraft-based remote sensing techniques are used to map the locations of potential holdover fires. However, these technologies struggle to detect smoldering ground fire, especially when it’s covered by frozen ground. The sensors can be calibrated to detect weak heat signatures, but this often results in numerous false positives. The true extent of holdover fires cannot be confirmed until validated on the ground. 

To address this technological limitation, the BC Wildfire Service assumes holdover fires could exist within the perimeter of any wildfire that was not fully extinguished in the previous season. We identify segments of these fire perimeters that could pose risk to neighbouring values. This allows the organization to focus remote sensing and aerial/ground patrol efforts in the right places to ensure the earliest detection of holdover fires in high-priority locations. 

BC Wildfire Service also relies on the public to report columns of smoke to 1 800 663-5555, *5555 on a cell phone or via the BC Wildfire Service mobile app. 

How we respond to holdover fires

Because these fires often burn in remote locations and typically stop emitting detectable heat signatures over the winter, they can be difficult to find. When the weather changes and crews are able to detect them, they can still be challenging to extinguish.  

The areas impacted by large-scale wildfires can be highly hazardous for firefighting personnel, with ash pits and significant potential for danger trees. Persistent, ongoing drought can allow fires to burn deep underground in rooting systems, causing massive amounts of root failure in all tree species. This significantly challenges suppression efforts and exposes crews to increased risk of falling trees. For more information on these challenges, see impacts of drought on forests in northern British Columbia. 

When a holdover fire resurfaces, it is usually contained to a very small part of the previous season’s fire perimeter. Because the actively burning area is much smaller than the past year’s burnt area, it is designated a new fire number on April 1 of the current fire season to accurately report a new fire size that reflects the current situation.

Our focus is early detection and suppression in areas along the edges of fire perimeters, as unburned fuels in these areas have the potential to ignite and prompt fire growth. We maintain preparedness by studying forecasts, analyzing trends and accounting for conditions that affect soil moisture, fine fuel dryness, vegetation growth and overall fuel availability. We continue to monitor these areas and will respond to any fire activity that has the potential to impact neighbouring values. 

When it is likely that incoming weather conditions will expose areas where holdover fires are still carrying heat, resources are proactively deployed to the area of concern. Crews use a combination of direct and indirect attack methods, as conditions allow, to respond to the holdover fires that resurface in the spring. We work in partnership with local governments, First Nations, industry and contractors to respond to holdover fires as they reemerge. 

As we move into the summer months, we will continue to monitor known holdover fires and prepare for the potential impacts of drought conditions in regions that saw larger fires in the previous season. Crews and resources will be strategically deployed to areas with the greatest fire risk. 

What have we learned and how will we address holdover fires moving forward?

The BC Wildfire Service and impacted communities began discussions around post-wildfire land-based recovery while wildfires were still burning in the 2023 season. These discussions helped us identify values near holdover fires and talk about potential actions with local leaders. 

We are continuously learning and working to enhance how we respond to emergencies in a rapidly changing world. The BC Wildfire Service’s Predictive Services Unit—a multi-disciplinary team of fire behaviour specialists, weather forecasters and IT and data analysts—leads our work to incorporate new tools and technologies that can help with challenging problems like earlier detection of holdover fires. Our Research and Innovation team works with academic and business communities to identify and develop new tools and techniques related to wildfire management.  

The way we respond to wildfire, including holdover fires, impacts everyone, and we will continue to work with all land users, First Nations and local governments to establish shared priorities and coordinate our response. The question of how to create a more resilient land base into the future is a broad one that includes BC Wildfire Service prevention, mitigation and recovery work, other Ministry of Forests initiatives as well as the work of FireSmart BC and others.  

The reality of fire on the landscape in B.C. demands a response broader than one single agency or government; what is required is a whole-of-society approach. Crucially, members of the public are our best asset in the detection of wildfires, including holdover fires. If you see smoke, fire or any dangerous activity that could lead to a wildfire, report this to 1-800-663-5555, *5555 on a cell phone or via the Report a Fire function on our mobile app.  

Wildfire resiliency is a shared responsibility. Learn more about the work underway in B.C. and what you can do to help prepare your property and community:

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Contact:

Provincial Fire Information Team
BC Wildfire Service | Ministry of Forests
250-312-3051
FIREINFO@gov.bc.ca 

Connect with the Province of B.C. at www.gov.bc.ca/connect.