Predicting how fire risks can go from fine to inferno

Fire risk as already changed as a result of global climate change and is likely to fuel even more change as feedback loops create disastrous consequences for both biodiversity and human populations.   Yet accurately predicting the risks and impact of fire globally is still a work in progress.

 

A team of Yale scientists and their colleagues in South Africa, Gabon, and United States set more than 1,000 fires in grassy savanna ecosystems where more than 80 percent of world’s fire activity occurs. Using the results, they tested a model that will help climate scientists to more accurately predict when and where changes to the fire regime are likely to occur, and how they will impact global climate change. They report the results June 20 in the journal Proceedings of the National Academy of Science.

 

“Areas such as American West and African savannahs can suddenly switch from a nonflammable state to one where everything is burning, or vice versa,” said senior author Carla Staver, associate professor of Ecology and Evolutionary Biology at Yale. “Predicting when that threshold will be crossed is crucial to understanding the impact fires have now and will have in the future.”

 

The Yale team led by Anabelle Cardoso, a post doc in Staver’s lab who is now at the University at Buffalo, set fires in Kruger National Park, in South Africa, and other savannas in Africa and the US, and measured variables such as grassy fuel biomass and moisture levels and air temperature and humidity as well as seasonal variables such as rainfall.

 

What they found is that fire spread is analogous to the spread of an infectious diseases and can be modeled the same way that public health officials predict disease outbreaks. Like infectious diseases, fires like require an ignition source (someone who initially contracts the disease), a minimum of fuel to burn (enough people in the population who are vulnerable to becoming infected), and advantageous environmental conditions to spread quickly (a disease that is very contagious and a susceptible population that is not engaged in minimizing transmition).

 

“And like a person previously infected, an area that has burned gains ‘immunity’ to future fires until sufficient amount of fuel re-grows,” Staver said. “Climate change affects this immunity because some places burn more and some stop burning. In both cases, biodiversity and ecosystem function is compromised.”

 

Fires thrive when moisture is low, temperatures are high and humidity is moderate to low.  All of these conditions can be exacerbated by global climate change, the authors say. When environmental conditions reach a certain threshold of available fuel and dry conditions, the risks of intense fires and dangerous fires can increase quickly, they found.

 

“Thresholds are like switches. Once it’s flipped, 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.”

 

Land managers who help manage fires intuitively understand these fire thresholds and how quickly fire conditions can change from safe to dangerous. However, many models used by nscientists to make predictions of the current and future global impact of fires don’t fully account fire thresholds and the release of carbon which could make it difficult to accurately predict future fire risks, the authors say.

 

 

Intriguingly, the impacts of global change, especially drought and increases in livestock grazing, have actually reduced the amount of fuel available for fires in some African savannahs.  However, other areas of the globe such as the American West are at far greater risk of catastrophic fires because fuels are drying out more.

 

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

 

The work of Staver’s lab with savanna fires are captured in this video produced by the Faculty of Arts and Sciences.

 

 

 

 

 

 

 

---

---