Wildfires are a natural part of many ecosystems globally, playing a role in forest health and regeneration. While fires have always been present, their patterns and characteristics are undergoing observable changes, presenting new challenges for ecosystems and human communities.
Shifting Patterns of Wildfire Activity
Wildfire activity globally is showing distinct changes. The frequency of extreme wildfire events, defined as those in the top 0.01% of intensity, increased 2.2-fold from 2003 to 2023, with the most extreme years occurring recently. While overall global area burned has declined, largely due to fewer low-intensity fires in African grasslands, fire intensity is worsening in specific regions, particularly in boreal and temperate conifer forests.
Individual fires are also growing larger, especially in the western United States, where the 10 years with the largest acreage burned have all occurred since 2004. This has led to a trend of fewer, but larger wildfires in the U.S., with 2015 exceeding 40,000 square kilometers burned for the first time in 25 years. The fire season has also extended, particularly in parts of the Western U.S., Mexico, Brazil, and East Africa, where it is nearly a month longer than it was 35 years ago. This lengthening is projected to continue globally.
Geographical expansion of wildfire activity is also evident, with regions previously less prone to large fires now experiencing increases. This includes areas like the Arctic, where rising temperatures contribute to increased burning. Data from Europe and Australia/New Zealand show a strong decline in area burned, while Southeast Asia, the Middle East, and boreal North America have seen increases of 3-4%.
Key Factors Influencing Wildfire Trends
Wildfire activity shifts are largely driven by climate change, fuel accumulation, and human actions. Climate change creates warmer, drier conditions, enhancing wildfire risk and extent. Rising temperatures, prolonged droughts, and changes in precipitation patterns contribute to drier soils and vegetation, making them susceptible to ignition and rapid spread. For instance, a 1-degree Celsius temperature increase in some Western U.S. forests could lead to a 600% increase in median burned area annually.
Historical fire suppression policies have altered natural fire regimes, leading to an accumulation of flammable vegetation, or “fuel,” in many forests. Denser forests with high fuel loads and drier conditions can result in more severe and extensive wildfires. Land use changes and logging practices also contribute to fuel accumulation, impacting the intensity and spread of fires.
Human activity plays a substantial role in wildfire trends, primarily through ignitions and wildland-urban interface (WUI) expansion. Approximately 84% of U.S. wildfires between 1992 and 2012 were human-started, expanding their spatial and seasonal range. The WUI, where human development meets wildlands, has grown globally by 35.6% since 2000, with 85% of this growth occurring between 2010 and 2020, increasing ignition sources and community vulnerability.
Broader Impacts of Changing Wildfire Regimes
The changing wildfire landscape has wide-ranging consequences for both natural environments and human societies. Ecologically, altered fire regimes can impact biodiversity, leading to changes in species dominance and potentially the loss of certain species. High-severity fires can hinder tree regeneration, reduce soil fertility, and increase soil erosion, harming water quality through increased sediment and nutrient runoff. Invasive species, such as cheatgrass, can further disrupt native plant communities and wildlife habitats by increasing fire frequency and intensity.
Wildfires also have significant atmospheric and climate feedback effects. They release large amounts of carbon dioxide and other greenhouse gases, contributing to air pollution and potentially exacerbating climate change. Smoke plumes, containing aerosols and particulate matter, can travel thousands of kilometers and affect air quality over vast regions and influencing atmospheric temperature structures. These aerosols can scatter or absorb solar radiation and alter cloud formation, impacting regional climate.
Human health and safety are directly affected by changing wildfire regimes. Smoke inhalation from fine particulate matter (PM2.5) can lead to respiratory and cardiovascular problems. Exposure to wildfire smoke has also been linked to increased emergency department visits for mental health conditions, including depression, anxiety, and mood disorders, with effects lasting up to seven days post-exposure. The direct threat to communities and infrastructure from intensifying fires also causes mental distress.
Economically, wildfires incur substantial costs. Federal fire suppression spending in the U.S. averaged $2.5 billion annually between 2016 and 2020. The total annual economic burden of wildfires in the United States is estimated to be between $394 billion and $893 billion, accounting for property damage, lost income, timber losses, and impacts on tourism and agriculture. These costs extend beyond immediate damages to include long-term recovery efforts and disruptions to various industries.