When the flames are out, danger continues: Cascading effects of wildfires

“When extreme event impacts are combined, their effect can be greater than the sum of their parts: This is exactly what we have seen in Australia with a long drought and the following fires that were only the first two links in a chain of cascading natural hazards,” says Kirsten Thonicke, a leading scientist at the Potsdam Institute for Climate Impact Research (PIK). “The fires were finally put out by heavy rain, which seemed like a good thing yet in some cases led to massive flooding. The water quickly eroded the dried-out soil exposed as a result of the fire. It washed earth, ash and burnt vegetation into rivers and lakes, in which the water quality subsequently deteriorated drastically.”

To better understand how natural hazards affect one another in complex ways, a team of scientists from PIK, the University of Potsdam, the Helmholtz Centre Potsdam GFZ and the Technical University of Berlin looked at the Manning River basin in New South Wales, southeast Australia, using satellite images as well as weather and river data.

“Wildfires are a normal natural hazard in Australia, yet, at the same time, they cause substantial economic and environmental impacts every year and play an important role in ecosystem processes – some plants require fires to sow,” says Matthias Kemter, lead author of the study from the University of Potsdam, and adds: “During 2019 and 2020, though, the Manning River catchment, like the rest of Australia, was affected by an unprecedented drought which increased the likelihood of very strong wildfires, way beyond normal. In a situation like that, it often only takes average rainfall to trigger drastic erosion, which stresses river systems and landscapes through flooding. All of these extreme hazards are likely linked to anomalous weather conditions driven by climate change.”

The hazard cascade observed in the Manning River catchment highlights that the impact of ongoing climate change on wildfires affects the likelihood and magnitude of disastrous consequences from other hazards. Also, the scientists showed that these hazards are in parts physically linked and triggered each other. 

Clearly, cascading hazards do not only exist in Australia: Last year, following Australia’s ‘Black Summer’, the western United States experienced its most-extensive fire season in 70 years, while extensive fires burned across Siberia. “Cascading effects represent an underestimated challenge in risk analysis, especially in view of the ongoing climate change,” Thonicke concludes. “Scientists and decision makers need to understand that the true cost of fire to society goes way beyond fighting only the flames - once the fire is out, the real environmental hazards start.”