Crossing the threshold of a fire can quickly make flames dangerous

Crossing the threshold of a fire can quickly make flames dangerous

Experimental fire in Lope National Park in Gabon. Credit: Anabel Cardozo

Global climate change has already exacerbated the risk of fire and is likely to fuel even more change, as accelerating feedback has catastrophic consequences for both biodiversity and the human population. However, accurate forecasting of the risks and impacts of shrubs and forest fires worldwide is still ongoing.

In a new study, a team of Yale scientists and colleagues from South Africa, Gabon and the United States have set more than 1,000 prescribed fires in grassy savannas, an ecosystem in which more than 80% of the world’s spill activity occurs. Using the results of experimental fires, they tested a model that will help climate scientists predict exactly when and where changes in the expected frequency and intensity of fires are likely to occur and how they will affect global climate change.

They announced the results on June 20 in the magazine Notices of the National Academy of Sciences.

“Areas like the American West and the African savannahs can suddenly go from a non-flammable state to one in which everything burns, or vice versa,” said senior author Carla Staver, an associate professor of ecology and evolutionary biology at Yale. “Predicting when this threshold will be exceeded is crucial to understanding the impact of fires that they have now and will have in the future.”

Yale’s team, led by Anabel Cardoso, a former doctoral student at Staver Laboratory and now at the University of Buffalo, set fires in the Kruger National Park in South Africa and other savannas in Africa and the United States. They then measure variables such as grass biomass, moisture levels, air temperature and humidity, and seasonal variables as it rains.

Crossing the threshold of a fire can quickly make flames dangerous

Observation of the spread of fire from above shows how completely a landscape burns under favorable conditions. Credit: Anabel Cardozo

Their findings, they say, show that the spread of fire is similar to the transmission of infectious diseases and can be modeled in the same way that public health officials predict disease outbreaks. Like infectious diseases, fires require a source of “ignition” (someone who is initially infected with the disease), a minimum of fuel to burn (enough people in the population who are vulnerable to infection) and favorable environmental conditions for rapid spread. a disease that is highly contagious and a sensitive population that does not try to minimize transmission).

“And as a person who has been infected before, an area that has burned down acquires ‘immunity’ to future fires until enough fuel grows again,” Staver said. “Climate change affects this immunity because some places burn more and others stop burning. In both cases, biodiversity and ecosystem function are compromised.”

Fires thrive when humidity levels are low, temperatures are high, and humidity is moderate to low. All of these conditions can be exacerbated by climate change, say the authors. When environmental conditions reach a certain threshold in terms of available fuel and dryness, the risks of intense fires and dangerous fires can increase rapidly.

“Thresholds are like switches. Once switched, everything changes quickly. It’s not gradual,” Cardoso said. “The risk of fire does not go from ‘low’ to ‘dangerous’ in small steps. Rather, it can go from “low” to “all-burning” without any warning signs. “

Credit: Yale University

Land managers with experience in fire management intuitively understand these fire thresholds and how quickly fire conditions can change from safe to dangerous. However, many models used by scientists to predict current and future global effects of fires do not fully take into account these thresholds and how much carbon is released during these burns, which can make it difficult to accurately predict future fire risks, the authors say. . .

Interestingly, the impact of global change – especially drought – and the increase in livestock grazing have actually reduced the amount of fuel available for fires in some African savannas. However, other parts of the globe, including the American West, are at much greater risk of catastrophic fires as fuels dry out more.

“The switch can work in both directions,” Staver said.

The loss of ancient grazing animals has caused a global increase in fires

More info:
Quantification of ecological restrictions on the spread of fires in grassland ecosystems, Notices of the National Academy of Sciences (2022). DOI: 10.1073 / pnas.2110364119.

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Yale University

Quote: Crossing the fire threshold can quickly turn flames into dangerous (2022, June 20), extracted on June 20, 2022 from .html

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