Fires 2022: understanding the dynamics of fires in Europe thanks to "pyroregions"


In Europe, the 2022 fire season was widely publicized and, in several countries, the area burned has been considered "unprecedented". But for the most part, these analyzes are not enough to support such conclusions.

A few months after these events, thanks to homogeneous data on climate and forest fires, we can recontextualize these fires of the summer of 2022: by summoning past events and analyzing how climate change could modify the activity of such events in the future.

Where does the burned area data come from?

Among the analyzes presented in the media, many are based on the EFFIS database (for European Forest Fire Information System).

This database collects burnt areas from different sources (satellites, national inventories), but suffers from major biases, in particular procedural changes in data collection over time in order to improve its quality. These biases hinder the analysis of long-term trends or the analysis of a specific year such as 2022.

Data from satellites is often used to examine continent-scale fires in because of their spatial and temporal coherence. However, it is important to recognize that these data underestimate fire activity, especially those smaller than 100 hectares which escape the detection of satellites. On the other hand, the data are homogeneous both in time and space, which allows comparisons to be made between different years and different regions.

For our work, we use thermal anomalies from MODIS satellites, available since 2001; this near real time indicator of fire activity is widely used in the scientific literature.

The 2022 fire season

By aggregating data over Europe and accumulating thermal anomalies since 1er January, we see with the help of the graph below that 2022 is above the average, but does not reach at any time of the year the maximum value observed during the last two decades.

For example, the thermal anomalies for the years 2003, 2007, 2012, and 2017 are much higher than in 2022. On a European scale, the year 2022 is thus within the historical range and is not "without previous", contrary to the impression relayed by many media.

Cumulative thermal anomalies across Europe. These daily anomalies are from MODIS Terra/Aqua sensors over the period 2001-2022 (last update August 31, 2022). They are a very good indicator of fire activity and burned areas. The gray envelope is the standard deviation (the spread of the data from the mean) and the dashed lines indicate the maximum and minimum values ​​over the historical period.
Provided by the author

What are the causes of extreme fires in Europe?

Remember that it is generally necessary three key factors for a fire to start and spread:

  • a source of ignition (in France, 95% of fire outbreaks are linked to human activities);
  • the presence of combustible material (vegetation that will feed the fire);
  • moisture content of plants and wind speed (which depend on weather conditions).

The influence of the first two factors does not change drastically from one year to the next. On the other hand, the variability of meteorological conditions largely explains the changes in burned areas from one year to the next.

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Extreme fire seasons are therefore generally associated with hot and dry climatic conditions that make the forest flammable. The co-occurrence of these conditions with a strong wind can amplify the fire risk.

These meteorological variables can be synthesized using the fire-weather indexnamed Fire Weather Index (FWI) and used by operational departments to measure the daily fire risk.

What are the fire regimes in Europe?

Locally, the occurrence of a fire is random, because it depends on human factors, which are often unpredictable. To overcome this difficulty, the fires are often aggregated on the scale of a region or a country in order to reduce this random dimension.

But the aggregation of fires in geopolitical units is not necessarily the most relevant for examining a natural risk. This is particularly true for fires in Europe, a very diverse continent in terms of climate, vegetation and human activities.

Distribution of “pyroregions” representing different characteristics of fire across the continent. Regions with more than 80% non-combustible surface (urban and agricultural surface) are shown in grey.
Provided by the author

This is why concept of “pyroregion” helps to better understand the spatial diversity of fire. A pyroregion has similar characteristics such as the size of the fires, their frequency, their seasonality or their intensity. These characteristics ultimately determine the impacts of fire on vegetation and society; they are often used to better understand the fire risk.

In a recent study, we have identified four distinct pyroregions on the scale of the European continent.

For example, the south of the Iberian Peninsula records large intense fires, but less frequent than the north of Portugal, where the frequency of fires and the area burned are the highest in Europe. In mountainous and traditionally pastoral regions, such as the Pyrenees, parts of the Alps or Scotland, the area burned can be substantial, but comes mainly from winter or spring fires (we speak of cool season fire) that rarely put ecosystems at risk.

Of course, these pyroregions do not follow administrative, ecological or climatic boundaries; they can be considered as a practical means of describing the fire regimes in space, which are relatively stable over the years.

The 2022 fire season seen through the prism of pyroregions

From June to August 2022, persistent heat waves affected parts of northwestern and central Europe, breaking temperature records and promoting fire activity.

In our work, we aggregated the fire-weather conditions (Fire Weather Index) as well as fire activity (measured by the number of thermal anomalies detected by satellite) at the pyroregion scale; we present below the deviations from the mean.

Fire-weather anomalies and fire anomalies observed in each pyroregion. Anomalies (expressed as a percentage) in fire activity (MODIS Terra/Aqua sensors) and in the fire-weather index, averaged over the June-August season compared to the historical average (2001-2021). The regression lines indicate the linear relationship between fire-weather index and fire activity at the pyroregion scale. Dotted lines indicate normal conditions.
Provided by the author

It can be said that the year 2022 is indeed "unprecedented" in the Pyroregion low-fire prone (the least affected by fires usually), with the highest number of fires detected in the last 20 years; 2022 comes second in the pyroregion cool season fire, usually subject to winter fires. On the other hand, fire activity is close to normal in the pyroregion highly-fire prone in southern Europe, the region most prone to fires.

The occurrence of fires in historically “immune” regions therefore undoubtedly contributed to the media hype during the summer.

Will climate change modify these pyroregions?

Pyroregions also provide a baseline for simulating future changes in fire regimes as the planet warms.

In another of our studies, currently being assessed, we show an increase in fire activity across the continent as a result of warming, according to previous work data.

For example, our results indicate a 50% greater increase in burnt areas in the northern Iberian Peninsula beyond a global warming of 2°C. In addition to the area burned, our analysis also reveals a sharp increase in fire frequency and intensity as well as a lengthening of the fire season, which will consequently alter current fire regimes.

These changes will lead to a spatial extension of the pyroregions most favorable to fires in southern Europe, with extensions of the order of 50% to 130% under a global warming of 2°C to 4°C. vs.

In a second scenario that we are studying, the increase in the area burned, the intensity of the fires and the lengthening of the season at risk by three additional months in certain parts of the Balkans, northern Portugal, Italy and southern France could undermine national firefighting capabilities.

This spatial extension of the risk zone could also have significant social and ecological repercussions in the absence of mitigation or adaptation measures.

Finally, agricultural abandonment and the abandonment of certain traditional practices, such as extensive livestock farming, are increasing the forest area and the quantity of biomass available for fire in southern Europe. This phenomenon, combined with urban sprawl and the development of habitat-forest interfaces, will not fail to increase our vulnerability to fires.

Luiz Felipe Galizia, PhD, Inrae; Francois Pimont, Research engineer, specialist in forest fires, Inrae; Julien Ruffault, Postdoctoral researcher on forest fires, Inrae; Renaud Barbero, Researcher in climatology, Inrae et Thomas Curt, Director of Forest Fire Risk Research, Inrae

This article is republished from The Conversation under Creative Commons license. Read theoriginal article.

Image credit: Shutterstock / evasion228 /Aubais, Gard, France - July 31, 2022: Fire in the maquis on the road between Aubais and Gallargues-le-Montueux.

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