Wildfire Causes
What causes wildfires?
While most wildfires of the past were sparked by lightning, the vast majority of modern wildfires are caused by human activity in some form. According to the US Federal Emergency Management Agency (FEMA) reports from 2014-2017, 50.8% of wildfires were caused by human activity. More recent estimates put this number at up to 85%.
Natural Cause: Lightning
Wildfires started by lightning mostly occur in “wildland” defined as land that has not been developed. Extreme weather like high heat, low humidity, and high winds lead to perfect conditions for “dry lightning”, lightning with no rain. These are also prime conditions for wildfire spread. Most wildland fires in the western US occur in the the summer when heat is high, rain is minimal, and dry vegetation is abundant.
Human Causes
The most common human causes of wildfires are industrial equipment malfunctions, discarded cigarettes, arson, uncontrolled prescribed burns, unattended campfires or burning debris, and vehicles.
How have humans contributed to this increase?
Historical Wildfire (Mis)Management
Most Indigenous Peoples of North America utilized frequent controlled fires for land and pest management which were critical for ecosystem health. These cultural burning practices were outlawed with settler colonialism and replaced with total wildfire suppression with the goals of preventing all wildfires and stopping their spread as quickly as possible. This directly led to the “wildfire paradox”, the fact that when more small fires are suppressed, dry fuel builds up ultimately leading to bigger fires. Now, the USDA Forest Service has adopted a “let burn” policy for small fires, but the policies of the past and and present still contribute negatively to today’s wildfires.
Increased Wildland-Urban Interface (WUI)
Human civilizations continue to rapidly encroach on undeveloped areas leading to an increase in the “Wildland-Urban Interface,” or the area where human-made life intermixes with wildland. This increases the risk of human-caused sparks igniting larger forest fires, poses unique challenges for firefighters, and means even small fires risk thousands of livelihoods.
Explore the map below. This shows wildfire risk to homes in the top 10 riskiest states in the US. You can compare the populations of individual counties to their risk to see how many people are being affected. This expansion of the Wildland-Urban Interface means that millions of homes in the US are directly at risk.
Click on a county or past wildfire to see the details. Past wildfire events are clustered in riskier areas. Also, wildfires that impacted more buildings are clustered in areas with higher populations.
Climate Change
The greatest contributor to increasing wildfires is climate change from fossil fuel emissions. This has led to warmer average temperatures and more frequent droughts and heat waves, ideal conditions for longer, hotter, and more destructive wildfires. It also contributes to the climate-fire feedback loop: more fossil fuel emissions mean a warmer planet leading to more wildfires contributing more carbon dioxide to the atmosphere.
Now that we know some of the main causes of increased wildfires, let’s look at its major effects.