Wildfires: “Climate change is providing the fuel”

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Ms. Böhnisch, this summer we’ve seen devastating forest fires raging across the world. What factors need to come together to enable these fires to happen?

Andrea Böhnisch: The groundwork may already have been done back in the winter, as was the case in Spain and France: The winter was relatively wet and mild, which allowed lots of vegetation to grow and build up early in the year. Large swathes of this vegetation then died off when the first heat waves of the summer hit. When heat and drought conditions combine, high temperatures in the atmosphere result in greater evapotranspiration, causing the soil and vegetation to dry out even more. When lots of biomass dies in conditions like this, there’s a huge amount of material that will burn.

If there’s then also wind that will fan the flames and allow fires to spread massively, the risk of large fires is very high. In research, we refer to a combination of multiple individual events such as this as a compound event. So typical fire weather that presents a high risk of intense fires would be hot, dry and windy. All that’s needed then is a spark to ignite the fire.

Why climate change contributes to wildfires

What impact is climate change having on the problem?

First and foremost, climate change is impacting the weather because it’s changing the meteorological conditions that exist before and after the fires. You could say it is providing the fuel. As well as higher temperatures in general, we’re also seeing a proliferation of certain weather conditions that occur in the summer months in particular: This is when areas of high pressure become almost stuck over regions of Central Europe for many days or weeks or slowly make their way from Western to Eastern Europe. This sometimes leads to the formation of heat domes: As the air sinks, it keeps getting warmer and this promotes higher levels of evapotranspiration, which can create a self-reinforcing system that produces even drier and warmer conditions, including in the soil.

In addition, climate change is altering the patterns of precipitation in many regions: We’re seeing drier summers and wetter winters. If they’re then milder as well, because the climate is generally getting warmer, the scenario we’ve already discussed will ensue: More vegetation can build up early in the year and this will then die off during dry hot summers and form flammable biomass.

So climate change increases the chances that a spark will in fact lead to a fire and there may be more frequent fires - but this is not inevitable because there also needs to be a trigger for a fire to occur.

The risk of wildfires in Germany

To what extent is climate change increasing the risk of large wildfires in areas where they have not previously occurred on this scale?

From a climatological perspective, we can say that the weather patterns and climate conditions that are more likely to create fire weather are becoming more frequent. This will also happen more often in Germany. But this isn’t enough to be able to predict the level of risk accurately. That’s because this also depends on the type of vegetation and on how healthy ecosystems like forests are. I think you need to differentiate at a smaller scale.

In general, regions that manage to retain water and moisture in the soil are more resistant to fire. This doesn’t mean that they are incapable of burning under any circumstances, but they’re under nowhere near as much threat as a completely parched landscape that contains lots of flammable material.

As we’ve seen in Bavaria this summer, it is also difficult for firefighting teams to access the seats of fires, especially in mountainous areas. Helicopters and aircraft are then needed to fight fires in rough terrain. Another issue is that the ecosystems in Germany and of course the management of them are also not necessarily well set up to deal with fires. In Bavaria, for example, I would describe the problem on this scale as a new phenomenon.

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What lies in store for Europe and Germany: Should we expect that large-scale wildfires will simply be part of our lives during future summers?

Yes. The climate is set to get much hotter and will also tend to be drier, which means that the climatic conditions in summer will increasingly promote a high risk of wildfires. In Germany, this will greatly affect the west and southwest in particular. In Bavaria, it will be mainly the north, but also the Alpine region, that will be affected by these climatic conditions.

It is apparent that compound events, for example simultaneously hot, dry and windy weather, are tending to affect wide swathes of Europe and the risk of fire is occurring synchronously in different regions. This may be relevant when it comes to capacities available across Europe for fighting fires or even access to water for firefighting given the widespread shortage of water, such as the water shortage we’re seeing right now.

Another new phenomenon in Europe are indications that fire storms can form in the hot air as it rises: The fires create their own weather, propelled dynamically by the fire.

How can societies adapt to these risks?

The meteorological risk and its impact on vegetation are one thing. However, there’s another aspect that can be influenced more directly because fires need triggers to spark them off. And in heavily used landscapes like in Europe, these triggers are unfortunately very often linked to people, their actions and their infrastructure.

In the future, people will need to coordinate across Europe and observe how countries that already have a significant problem with fires manage to deal with the issue. It’s about having structures, plans for managing ecosystems, but also about how people living in at-risk areas behave. Anyone can be the spark that ignites the fire.

Dr. Andrea Böhnisch conducts research on drought, heat and compound events at LMU’s Faculty of Geosciences.