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Lightning fires threaten northern forests

9 November 2023
In the summer of 2023, vast areas of Canada’s forests were on fire. Many of these fires were ignited by lightning. In a new global study, researchers now reveal that this was not a coincidence as they uncovered insights into the growing danger posed by lightning-induced fires to temperate and boreal forests. The study shows that most fires in these forests are caused by lightning strikes and that lightning will likely increase in these regions with climate change.

Researchers at VU Amsterdam, together with colleagues from the Netherlands, the United Kingdom and China, found that most fires are lit by humans, for example in tropical savanna regions and Europe. However, lightning fires clearly dominate the more remote temperate and boreal forests. Until now, we did not know where in the world people or lightning are the predominant ignition source for wildfires. The study is the first to provide a global map of the distribution of human and lightning fires on Earth. The findings are published in the journal Nature Geoscience.

Lightning fires
‘’What many people may not be aware of is that lightning is the most common ignition source for fires in remote temperate and boreal forests” says Thomas Janssen, research associate at VU Amsterdam. These forests store large amounts of carbon, which is released in the form of greenhouse gases during the fire. The research reveals that 77 % of the burned area in intact forest regions outside the tropics is due to lightning fires, and the number of strikes is expected to increase by 11 to 31 % per degree warming with ongoing climate change.

Can we control fires?
The researchers mapped the contribution of lightning versus human ignitions as fire causes across the globe. A very important map, as it shows where we can directly control fires by limiting ignition and managing vegetation. Most fires in tropical savannas and Europe are for example ignited by people. In these regions it must be possible to mitigate the negative consequences of fires by limiting the number of ignitions and managing fuels. Also, another recent study, co-authored by Sander Veraverbeke, associate professor in Climate & Ecosystems Change at VU Amsterdam, laid out where fuels have an important control on fire occurrences. Fuel management could reduce negative impacts of fires in for example tropical savannas and European forests. This won’t stop the lightning in remote forests; to halt further increases in these lightning fires, global climate action is the only solution.

Temperate and boreal forests at risk
“Temperate and boreal forests are globally important as they, together with tropical forests, represent some of the few intact forests left on our planet”, says Veraverbeke. “They are often biodiversity hotspots and store large amounts of carbon in trees and soils.” By using satellite observations and computer models, the research team also found that forest losses from fires in northern regions are already among the highest on Earth. “When these forests do not fully recover after fires, the carbon that was stored in these forests is emitted and remains into the atmosphere, where it can further accelerate climate change.” This could initiate a potentially vigorous feedback loop. In earlier research, Veraverbeke and colleagues had already found that climate change leads to more lightning in high latitude regions. This finding was now further confirmed.

The contributions of the VU authors Thomas Janssen and Sander Veraverbeke to the two studies were funded by the Dutch Research Council through a Vidi grant and the European Research Council through a Consolidator grant under the European Union’s Horizon 2020 research and innovation program.