Canadian wildfires persist because of a combination of underground smoldering in carbon-rich soils, a fire season that has grown longer by more than two weeks since the 1960s, and drought conditions that keep fuels dangerously dry. Some fires never actually go out at all. They burrow into deep peat layers, survive beneath snow through the winter, and reignite on the surface when spring arrives.
Zombie Fires That Survive the Winter
The most surprising reason Canadian wildfires keep burning is that some of them literally overwinter underground. Known as holdover fires or “zombie fires,” these occur when surface flames die out but smoldering combustion continues deep in peat-rich soil. The smoldering front creeps through organic material slowly, generating enough heat to stay alive but not enough to produce visible flames. When snow falls, it actually insulates the underground burn, trapping warmth in the soil and allowing the fire to persist for months.
When temperatures rise in spring and the ground dries out, these buried embers work their way back to the surface and rekindle. A fire that appeared to be fully extinguished in October can produce new flames in April or May, sometimes kilometers from where it was last seen. This is one reason fire agencies report “new” fires in areas that burned the previous year. They aren’t new at all.
Detecting these fires during winter is extraordinarily difficult. Satellites that use infrared imaging can spot typical wildfire temperatures, but persistent cloud cover, snow, and frozen soil interfere with every available sensor. Microwave instruments that measure soil moisture fail when the ground is frozen. Researchers at the Naval Research Laboratory have attempted to combine multiple satellite wavelengths to find overwintering fires and have so far been unable to identify reliable signatures. That means zombie fires can smolder undetected for an entire winter before surprising communities in the spring.
Why Peat Burns So Differently
Canada’s boreal forest sits on top of vast peatlands, some of the largest on Earth. Peat is partially decomposed plant material that has accumulated over thousands of years, packed into dense, carbon-rich layers that can extend meters below the surface. This fuel behaves nothing like the trees and brush people picture when they think of wildfires.
Smoldering combustion in peat is fundamentally different from flaming fire. It burns at lower temperatures, spreads more slowly, and is far less dependent on moisture to keep going. While flaming fires need relatively dry fuel to sustain themselves, smoldering reactions can persist in much wetter conditions. That’s what makes peat fires so hard to extinguish. Water applied to the surface doesn’t necessarily reach the smoldering front deep in the soil.
Two factors control how deeply peat burns: moisture content and density. Denser peat actually supports deeper burning because it holds more combustible material per unit of volume. The only reliable check on this process is high soil moisture. When peat is both dense and wet, it resists deep burning. But during drought years, that moisture barrier disappears, and fires can consume organic soil layers that took centuries to form. Research on boreal peat combustion found that moisture and density together explained about 79% of the variation in burn depth, making drought the single most important factor in whether a peat fire stays shallow or becomes a deep, long-lasting problem.
The Carbon Cost of Underground Burning
What makes smoldering soil fires particularly consequential is how much carbon they release. A study published in Biogeosciences estimated that during Portugal’s 2022 fire season, belowground smoldering accounted for roughly 52% of all CO₂ emissions from wildfires. That means the fires burning invisibly underground released as much carbon as all the visible, flaming surface fires combined. Peat and organic soil matter alone were responsible for about 35% of total fire emissions measured in CO₂ equivalents.
Canada’s peatlands store an enormous share of the world’s terrestrial carbon. When those stores burn, they release carbon that was locked away for millennia, and unlike a forest that can regrow in decades, peat accumulates at a rate of roughly one millimeter per year. Carbon released from deep peat burning is effectively irreplaceable on any human timescale.
A Fire Season That Keeps Getting Longer
The Canadian fire season has expanded significantly over the past half century. A national analysis spanning 1959 to 2015 found that the season now starts about nine days earlier and ends roughly seven days later than it did in the late 1950s. That’s more than two additional weeks of fire weather each year. Over the same period, large fires have been getting larger.
This expansion is driven by warmer temperatures, earlier snowmelt, and longer stretches of dry weather. Canada’s northern regions are warming two to three times faster than the global average, a phenomenon known as Arctic amplification. Warmer springs mean snow disappears sooner, exposing dead grass and forest litter to drying conditions weeks before green vegetation emerges. Warmer summers pull more moisture out of soil and living plants. The result is a landscape that is primed to burn for a longer portion of the year.
Drought Sets the Stage
Persistent drought across parts of Canada has compounded the problem. Agriculture and Agri-Food Canada’s drought monitoring shows regions like Ottawa receiving approximately 25% less precipitation than average. When precipitation deficits persist across multiple seasons, they don’t just dry out surface fuels. They lower water tables, drain moisture from deep peat layers, and reduce the natural firebreaks that wet areas normally provide.
Southern Alberta and southeast British Columbia entered 2026 with significant snow-free areas and exposed grasslands well ahead of the typical schedule. A warm, dry stretch kicked off fire weather tracking unusually early. In early February, a roughly 275-hectare fire was burning northwest of Calgary, a size that is uncommon for that time of year in Alberta. These early-season fires are a direct consequence of inadequate snowpack and persistent dryness.
Why Not All Fires Get Fought
Canada is the second-largest country on Earth, and much of its boreal forest is remote wilderness with no roads, no communities, and limited economic value. Fire management agencies use a priority system to decide which fires to suppress and which to monitor. Residential areas, high-value commercial forests, and recreational sites get the most protection resources. Fires burning in remote wilderness parks or forests with limited economic value are often allowed to burn naturally, unless rare habitat or culturally significant areas are threatened.
This triage approach is a practical necessity. Canada simply doesn’t have the resources to fight every fire across millions of square kilometers of forest. In severe fire years, even priority areas can be overwhelmed when dozens of fires ignite simultaneously. Fires in remote areas can burn for weeks or months, contributing to haze and air quality problems hundreds of kilometers downwind, without anyone actively working to put them out.
What the 2026 Season Looks Like
Forecasters currently rate significant fire potential as normal across most of Canada for early 2026, but several warning signs are already visible. British Columbia’s interior and parts of Atlantic Canada extending into southern Quebec are expected to receive below-normal precipitation. The dry signal over British Columbia is likely to spill into southern Alberta, worsening already dry conditions there. April precipitation is forecast to be relatively scarce across most of the country, limiting the spring moisture that normally slows the onset of fire season.
The North American Seasonal Fire Assessment notes that despite the unusually early fire activity, conditions haven’t yet crossed the threshold for an above-normal outlook. But forecasters are watching closely. Warmer and drier than normal conditions are expected to continue in multiple regions, and any fires that overwintered underground from the previous season could add to the early-season fire count in ways that are difficult to predict or prevent.