Don‘t take your eyes off burnt soil!

International Soil Day

This Monday is the 5th of December. It is International Soil Day, and therefore it is more than adequate to address burnt soil as the big issue it represents.

A common thing, is to worry about all of the damage a wildfire is going to cause while it happens. For example, all the different animal species that can end up harmed or even dead, the plant specimens that are destroyed and especially humans or goods that can get affected by the fire. Something that is not as usual as what previously mentioned, is the question: What happens to the soil? Maybe we do ask ourselves this question but, do we do it correctly?

Every year, wildfires burn millions of hectares of land, to be more exact, 448 million hectares. An interesting fact is that almost two millions of the burned hectares correspond to Europe and to the United Kingdom. Also, due to the future rise of global temperature and therefore drier climate, the fire risk is increasing and so is the soil erosion.

What happens after a wildfire?

After a wildfire, there are some things that are considerably important to notice; the soil seepage is reduced. Therefore, the probability of flooding and the creation of debris rivers grows. Floodings represent a big threat to the nearby towns and also to the ecosystems. The soil is less protected due to the loss of the vegetation layer that has been destroyed. And most importantly, the destabilization of the chemical balance of the soil due to the high temperatures. Combustion also has a big impact.

All these consequences and their degree of severity are strongly connected to two factors: the burn severity level and the geographical regions. If the burn severity levels are high, on-site erosion increases considerably as well as off-site impacts. Despite being regarded as an important hydrological and geomorphological agent, post-fire erosion assessments are mostly evaluated using model-based soil erosion assessments. They made them using much larger spatial scales; for example European or Global scales. These models take into consideration several post-fire erosion drivers. However, most of them fail to address burn severity and vegetation recovery among other factors. Therefore, the entire soil erosion budget, normally fails to be addressed.

Soil erosion after the fire

After a wildfire, the area that is affected can‘t normally be used, this leads to the abandonment of the area. Something that is also common is the appearance of periodic droughts and economic and social losses. The absence of appropriate land management also plays a big role. All of this combined, make soil degradation worsen. After the first year since the wildfire happens, according to data, 19,4 million Mg of additional erosion are lost when compared to the unburned conditions data. Moreover, after five years post-fire the final sum reaches the 44 million Mg of additional erosion. This ongoing erosion, leads to the fact that 46% of the burnt areas end up not showing any sign of full recovery over the time period of five years.

With the help of post-fire mitigation techniques, all the different impacts will hypothetically increase up to 63 to 77%. This would make it possible for the soil erosion levels to be almost the same as the pre-fire levels in only a time period of 4 years.

The main goals should be implementing and creating objectives. The final aim is to reduce post-fire degradation as identified in the European Union Soil, biodiversity and forest strategies.