Perennial forest fires in Africa fueled by aerosol reactions

Africa is on fire. This has been the case for thousands of years. The continent contains on average more than 50% of the Earth’s total land area burning, and there is no sign of it stopping; indeed, the season of forest fires in Africa, which move from one hemisphere to another, continues to increase.

The fire essentially feeds itself in a sort of feedback loop since the aerosols, induced by the perpetual fire, interact with the climate. This is a process that plays a critical role in regulating African ecosystems, enhancing wildfires and paving the way for increased fire seasons in subsequent years.

Aerosols are tiny particles that have a significant impact on Earth’s climate. They include a wide range of materials. In addition to the air pollution of human origin that we can observe (brown smog is the interaction of light with aerosols), there are many natural aerosols: salty sea spray, mineral dust, volcanic ash and smoke from forest fires. forest.

Suspended in the atmosphere, the role of aerosols in our climate is complex. But a new study led by Georgia Tech researchers demonstrates the role they play in the life cycle of wildfires in Africa. The research, published in the journal iSciencecould have significant implications for understanding the impacts of fire and climate change in Africa and other wildfire-prone regions of the planet.

“We previously thought that aerosols had a localized short-term climate impact and could be effectively removed by precipitation within a week. But in this study, we show that this is not necessarily accurate,” said Yuhang Wang, professor in the School of Earth and Atmospheric Sciences and corresponding author of a new study titled “Positive regional climate feedback improves wildfires in Africa.”

The Wang lab is working to solve the mysteries of air pollution, and the team is close to finding something with their latest research, revealing new clues in their study of wildfires in Africa, where the unique alternation between Dry and wet seasons along the equator extend the life of aerosols. .

“Basically, with the combination of wildfires and fire-induced aerosols, the impact of aerosols may be more long-term, extending across seasons,” said Wang, whose team invented the the tool she needed to carry out her investigation.

Build a better model

Several years ago, Wang’s lab developed the Regional-Specific Ecosystem Feedback Fire (RESFire) model to augment the existing, publicly available Community Earth System Model (CESM). Managed by the National Center for Atmospheric Research, CESM is an open-source global climate model that provides computer simulations of the Earth’s climate system.

RESFire enhances CESM’s fire simulation capability, helping researchers better understand complex fire-climate-ecosystem interactions, “which are not yet very well understood,” said Wang, whose team used its model CESM-RESFire to study aerosol feedback in Africa for latest research.

“We found that the extension of aerosol lifespan in Africa occurs through a positive feedback mechanism,” Wang said.

Aerosols can essentially give clouds a serious case of constipation, by absorbing vapor from the atmosphere and reducing the growth of large cloud droplets, making it difficult for clouds to produce large droplets.

“Fire aerosols are transported from hot or dry regions to humid regions,” Wang explained. “This leads to reduced precipitation and drying of fuel loads.”

The feedback mechanism

The identification of the positive fire-aerosol feedback mechanism in Africa sheds light on the climate feedback linked to wildfires on a global scale. Other studies have shown that in some coastal areas, such as the western United States, smoke from wildfires changes local fire conditions, leading to positive responses. These coastal regions have distinct fire seasons, and escalation caused by aerosol returns does not persist until the next fire season.

Africa is different. With changing fire regions and prevailing winds, positive feedback affects the current season and amplifies fires the following season. And the fire season has increased by up to 40% in Africa over the past four decades, meaning there could be changes in the distribution and variability of burned areas.

“The good news is that this mechanism is self-sustaining. It even has some resilience built into it,” Wang said. “The question is what happens in the presence of persistent global climate change. What we know is that the mechanism underlying this natural system of wildfires depends on the current state of the atmosphere.”

The positive feedback mechanism implies that a hotter, drier climate will likely lead to more persistent fires in Africa in the future, the researchers write, concluding: “The systematic feedback between fire and climate may also be present in other fire-prone tropical regions and has significant ramifications for understanding the impacts of fire and climate change on humans and plant life.