Research Paper Summary: Spikes in UK Wildfire Emissions Driven by Peatland Fires in Dry Years
- Rob Beeson
- Jun 12
- 7 min read
The research paper “Spikes in UK wildfire emissions driven by peatland fires in dry years” focusses on the impact of wildfires on carbon released into the air in the UK from 2001 to 2021, looking especially at peatlands.
The study found that fires in peatlands are the main reason for carbon emissions from fires in the UK, particularly during dry years.
These fires release large amounts of carbon stored in the soil, which then takes hundreds of years for the environment to absorb back. Looking ahead, if global temperatures rise by 2°C, carbon emissions from peatland fires could go up by over 60%, even if the size of the burned areas doesn't increase.
This poses a major challenge to the UK's goal of achieving net-zero emissions. The study highlights a clear need for better ways to manage and prevent wildfires in peatlands.
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Why Peatland Fires Release So Much Carbon
Big Impact: Peatland fires release a much larger share of the UK's total carbon emissions from fires than their size might suggest.
Between 2001 and 2021, an estimated 800,000 tonnes of carbon were released from peatland fires.
These fires often contributed up to 90% of all carbon emissions from fires in the UK each year.
Carbon in the Soil: On average, about 70% of all carbon released from UK fires comes from burning carbon stored in the soil. In some years, this can even reach 81%.
Packed with Carbon: Even though fires in other areas like moorlands might cover a bigger area, peatlands release the most carbon because their soil is incredibly rich in stored carbon.
Long-Term Problem: When peatlands burn, the carbon lost takes centuries to be absorbed back into the ground. This makes protecting them vital for slowing down climate change.
How Weather Drives Big Spikes in Emissions
Year-to-Year Changes: The amount of carbon released by fires varies a lot from one year to the next. Sudden big increases in emissions are clearly linked to very dry years.
Linked to Fire Weather:
The total area burned in summer and autumn is connected to a measure called the Fire Weather Index (FWI).
Burned areas in winter and spring are linked to the Initial Spread Index (ISI).
The FWI for a year was also directly linked to the amount of carbon released from soil.
Extreme Years: The year 2003 was particularly bad, with both soil carbon emissions and the Fire Weather Index being nearly eight times higher than the average, and more than 200% higher than the average for 2001–2021. Other years with high emissions included 2007, 2009, and 2019.
Soil Wetness Matters: How deep peat burns, and therefore how much carbon is released from the soil, is largely controlled by how much moisture is in the peat. Drier conditions cause fires to burn deeper, leading to much greater carbon loss.
The estimated depth of peat burnt varied between 0.9 cm (when wet) and 8.0 cm (when dry).
In wet years, like 2012 and 2014, there were much lower, or even no, carbon emissions from soil. This shows a strong link between moisture levels and fire activity in peatlands.
More Fires and Longer Fire Seasons
Growing Number of Fires: The number of fires in the UK has been steadily increasing each year from 2014 to 2021.
The number of fires doubled from 114 in 2020 to 234 in 2021.
Fire Season Gets Longer: The time of year when fires occur has also stretched out.
Between 2011 and 2016, fires were recorded in 1 to 4 months of the year.
But between 2017 and 2021, fires were recorded in 6 to 9 months of the year.
The longest fire seasons were seen in 2020 and 2021.
Scotland Most Affected: This lengthening of the fire season is most noticeable in Scotland, where peatlands cover about 23% of the land and account for about 45% of the total burned area in the UK.
What to Expect with Climate Change
More Emissions with Warmer Climate: If global temperatures rise by 2°C, predictions for future soil moisture show a significant increase in carbon released from UK peatlands.
This is because warmer conditions would cause peat to dry out, leading to deeper burns and an over 60% increase in fire-driven carbon emissions just from deeper burns.
The estimated average yearly emissions under these future conditions would be 18.3 kilotonnes of carbon, up from 11.1 kilotonnes historically (2001-2021).
Estimates are Low: The study's estimates for future emissions are often cautious and may be lower than what actually happens. This is because they assume the total area burned or where fires occur won't change, and they don't fully account for shallow peats or areas that might become drier due to drainage.
For example, a fire in Flow Country in 2019 was estimated by the model to burn 1.8-2.0 cm deep, but real measurements in the field showed burns of about 8 cm in natural peatlands and as much as 25 cm in drained areas. This suggests the model's estimate of 96 kilotonnes of carbon for that event could be as high as 195 kilotonnes in reality.
Huge Impact: The projected 61% increase in carbon emissions from soil under a 2°C global warming scenario would release about 3.8 million tons of carbon dioxide annually. This is like adding the average yearly emissions from 133 commercial airplanes, 820,800 passenger cars, and 414,000 homes.
What We Still Need to Learn and Do
Burned Area vs. Emissions: The research shows that the total area burned by fires doesn't always directly match the total amount of carbon released. While moorlands and heathlands might have larger burned areas, the years with the highest overall emissions are those where the most carbon is lost from peatlands.
Better Measurement Needed: There's a major gap in research when it comes to accurately measuring the carbon lost from ecosystems that used to be too wet to burn. This is especially important for understanding the full effect of climate change on carbon emissions.
Protecting Peatlands is Key: Protecting peatlands from fires is seen as an affordable way to slow down climate change by preventing future emissions. This highlights how crucial fire management is for reaching net-zero goals.
Northern Peatlands at Risk: Peatlands in northern areas, including those in the UK, are becoming more vulnerable to high emissions because temperatures are rising quickly.
Important Facts and Figures
UK Peatland Carbon Storage: UK peatlands store an estimated 3.2 billion tonnes of carbon.
Peatland Coverage: Peatlands cover 9% of the UK's land area and make up about 13% of the world's blanket bogs.
Historical Emissions (2001-2021):
Average yearly carbon emissions from fires: 44.8 kilotonnes of carbon.
Total carbon released from peatland fires: 0.8 million tonnes of carbon.
Peatland fires accounted for about 25% of the total average burned area.
Carbon from soil made up about 70% of all UK carbon emissions from fires on average.
Major Emission Spikes:
2003: 337 kilotonnes of carbon (nearly 8 times the average), with 300.8 kilotonnes from soil carbon.
2019: Total emissions between 16.5 and 20.6 kilotonnes (from aboveground vegetation) and 96.5 kilotonnes from soil carbon.
Projected Emissions (if global warming reaches 2°C):
61% increase in peatland carbon emissions.
Projected average yearly carbon dioxide release: ~3.8 million tons.
Projected total carbon emissions (if burned area stays the same as historically): 1031–1163 kilotonnes of carbon.
Burn Depths:
Average measured burn depth in UK peatlands: ~8 cm.
Model estimated burn depths for soil carbon: 0.9 to 8.0 cm.
How the Study Was Done
The study used a detailed method to estimate carbon losses from UK fires between 2001 and 2021.
Data Used: The researchers combined high-resolution maps showing peatland areas, vegetation types, and farmland. They also used information on soil moisture levels and data on where and when fires happened.
Emission Model: A computer model was used to calculate fire emissions, specifically set up for UK environments.
Aboveground Emissions: Carbon released from burning plants and trees above ground was estimated using existing models and by calculating how much carbon was in different types of vegetation and how completely it burned.
Soil Carbon Emissions: These were calculated based on how deep the peat burned, how much carbon was in the peat, and what portion of the peatland caught fire. The burn depth was figured out based on soil moisture content using a mathematical rule, which was adjusted to match actual observed burn depths in the UK (capped at 8.0 cm for cautious estimates). A cautious estimate for how completely the peat burned was also used (0.5).
Weather Data: Fire Weather Index (FWI) and Initial Spread Index (ISI) data were used to see how fire activity was linked to weather conditions.
Future Predictions: To predict future emissions, the study used projected changes in soil moisture from UK climate forecasts for a 2°C global warming scenario. They applied the soil burn depth calculations without changing the total burned area or fire locations, to specifically look at how changes in soil moisture alone would affect emissions.
Conclusion
This research clearly shows that UK peatlands are hugely important for the country's carbon balance. Their susceptibility to wildfires, especially when the climate is drier, poses a major threat to efforts to fight climate change.
The predicted large increase in carbon emissions from peatland fires due to global warming underlines the urgent need for better peatland protection and fire management strategies. This is essential to prevent massive carbon losses that would be very hard to reverse.
The findings also serve as a warning sign for other peatlands in similar climates around the world that are facing similar climate change impacts.
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