Crossing the threshold of a fire can quickly make fires dangerous

Crossing the threshold of a fire can quickly make fires dangerous

Crossing the threshold of a fire can quickly make fires dangerous

An experimental fire in the Lopé National Park in Gabon. Credit: Anabelle Cardoso

Global climate change has already exacerbated fire risk and is likely to fuel even more change, as accelerating feedback loops have disastrous consequences for biodiversity and human populations. Yet accurately predicting the risks and impact of bush and wildfires globally is still a work in progress.

In a new study, a team of Yale scientists and colleagues from South Africa, Gabon and the United States set more than 1,000 prescribed fires in savannah grasslands, an ecosystem where more than 80% of global fire activity. Using the results of the experimental fires, they tested a model that will help climatologists more accurately predict when and where changes in predicted fire frequency and intensity are likely to occur, and how they will have a impact on global climate change.

They report the results on June 20 in the newspaper Proceedings of the National Academy of Sciences.

“Regions such as the American West and African savannahs can suddenly go from a non-flammable state to an all-burning state, or vice versa,” said lead author Carla Staver, associate professor of ecology and biology. scalable at Yale. “Predicting when that threshold will be crossed is crucial to understanding the impact that the fires are having now and will have in the future.”

The Yale team led by Anabelle Cardoso, a former postdoctoral associate in Staver’s lab who is now at the University at Buffalo, set fires to Kruger National Park, South Africa, and other savannahs in Africa and in the United States. They then measured variables such as grassy fuel biomass, moisture levels, air temperature and humidity, as well as seasonal variables such as rainfall.

Crossing the threshold of a fire can quickly make fires dangerous

Monitoring fire spread from above shows how well a landscape burns under favorable conditions. Credit: Anabelle Cardoso

Their findings, they report, indicate that the spread of fire is analogous to the transmission of infectious diseases and can be modeled in the same way that public health officials predict epidemics. Like infectious diseases, fires require a source of “ignition” (someone who initially contracts the disease), a minimum of fuel to burn (enough people in the population likely to be infected), and favorable environmental conditions to spread quickly (a highly contagious disease and a susceptible population that does not seek to minimize transmission).

“And like a previously infected person, an area that has burned gains ‘immunity’ to future fires until enough fuel regrows,” Staver said. “Climate change affects this immunity as 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 high, and humidity moderate to low. All of these conditions can be exacerbated by climate change, the authors say. When environmental conditions reach a certain threshold in terms of available fuel and dryness, the risk of intense fires and dangerous fires can increase rapidly.

“Thresholds are like switches. Once activated, everything changes quickly. It’s not gradual,” Cardoso said. “Fire risk does not go from ‘low’ to ‘dangerous’ in small increments. Rather, it can go from ‘low’ to ‘everything is 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 the current and future global effects of fires do not fully account for these thresholds and the amount of carbon released during these burning events, which could make it difficult to accurately predict future events. future fire hazards, according to the authors. say.

Curiously, the impacts of climate change – particularly drought – and an 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 higher risk of catastrophic fires as fuels dry out more.

“The switch can work either way,” Staver said.

The loss of former grazers has sparked a global rise in fires

More information:
Quantify environmental limits to the spread of fire in grassland ecosystems, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2110364119.

Provided by Yale University

Quote: Crossing Fire Threshold Can Quickly Turn Blazes Dangerous (June 20, 2022) Retrieved June 22, 2022 from

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