A research co-led by the Desertification Research Center (CIDE, CSIC-UV-GVA) describes the mechanisms that make large fires possible
Climate appears as one of the main triggers by favoring fuel flammability, drought conditions and the effectiveness of ignitions.
An article recently published in the journal Frontiers in Ecology and the Environment of the Ecological Society of America (USA) sets out the ingredients and mechanisms necessary for large wildfires to occur. Four ingredients are required: ignition, fuel, drought and appropriate weather conditions. The study establishes a model showing how these four ingredients are related, and argues that climate change increases the ideal conditions for large fires. The work is co-led by the Desertification Research Center (CIDE), a joint center of the Spanish National Research Council (CSIC), the University of Valencia and the Generalitat Valenciana.
The paper proposes a model that describes how large wildfires occur. This model establishes that large fires occur when three thresholds are crossed simultaneously: ignition, fuel availability and drought. According to the study, these three thresholds decrease and are more easily crossed with certain meteorological conditions, such as dry winds (for example, westerlies in the Valencian Community) and high temperatures (favored by climate change).
Once these three thresholds are crossed, fires are generated that can be of great magnitude (mega-fires), generate their own dynamics (the so-called ‘firestorms’), and exceed the firefighting capacity of firefighters. “These conditions have occurred on several occasions in the Valencian Community, and it is foreseeable that they will be amplified in the coming years as climate change progresses,” says Juli G. Pausas, CSIC researcher at CIDE and co-author of this study with Jon Keeley, of the U.S. Geological Survey.
Weather conditions appear as a trigger for fires to occur in a given ecosystem, as they lower the thresholds for the other three ingredients. According to this study, climate change in the form of drought and high temperatures means that fewer ignitions and less fuel are needed to start large forest fires. In the same direction is the fact that more and more tropical hurricanes are reaching the coasts of the Iberian Peninsula, which favors the spread of fires.
“It is important to keep in mind that ignition and weather conditions conducive to fires are not enough for large fires; extensive and flammable biomass is also needed,” explains the CIDE researcher. The availability of this ‘fuel’ is affected by the topography, the type of vegetation, its structure and human use of the forest, among other factors. “A certain continuity of fuel is required for large fires to be generated, and in the Valencian Community, as well as throughout the Mediterranean basin, this continuity is generated mainly by rural abandonment, by the reduction of agriculture and grazing,” says Pausas.
Managing the triggers of major fires
Thus, climate change not only affects fire behavior (making them more intense), but also influences the increase in fire size and duration, as well as the temporal window in which large fires can occur. Among the conclusions drawn from the study that may be useful for managing the triggers of these large fires, the authors suggest that avoiding just one of these key factors for a large wildfire to start (ignitions, drought, or fuel continuity) could significantly reduce the likelihood of wildfires occurring.
"It is important to reduce ignitions in areas where wind plays a preponderant role in generating large fires. On the other hand, generating fuel discontinuities, the so-called mosaics, is more relevant in ecosystems where drought is key to fires," reveals Pausas. The researchers propose that, when modification of these factors is not possible, fire danger zones should be designated where human activity is minimized, as is now done in areas near active volcanoes or in areas prone to flooding.
Reference:
Juli G Pausas, Jon E Keeley, Wildfires and global change, Frontiers in Ecology and the Environment, DOI: https://doi.org/10.1002/fee.2359
CIDE Communication
