People started a staggering 84 percent of all wildfires in the United States, a new study reveals.

In the comprehensive, first-of-its-kind analysis of wildfire data over a 20-year period, the remaining 16 percent of fires started naturally or via lightning.

Human-Ignited Fires In Focus

University of Massachusetts professor Bethany Bradley and her coauthors probed 1.5 million wildfires occurring from 1992 to 2012, findings that human-induced fire season was triple the length of lightning-induced season and added 40,000 wildfires annually on average.

These fires accounted for nearly half or 44 percent of burned areas, they added.

According to the team, humans are expanding fires into more sites and environmental conditions than lightning can reach. They “create sufficient ignition pressure for wetter fuels to burn” and grew the so-called fire niche — which measures ignition sources, fuel mass and dryness — into places with “historically low lightning strike density,” the authors wrote.

The study, which focused on wildfires that required firefighters to be suppressed and not ones allowed to burn in remote areas, also found that fighting wildfires in the country has cost more than $2 billion in recent years.

“Fires are burning earlier in the spring in the Southeast and later in the fall in the West,” co-lead author Jennifer Balch of University of Colorado added in a USA Today report.

In the previous decade, a series of costly, fatal, and massive fires seared in western United States, and states such as Oregon, Washington, California, and Colorado saw some of the biggest wildfires ever documented.

What’s Left To Do Now?

Contrary to popular belief, human-induced wildfires are surprisingly common far into the spring and fall, and that lightning-induced ones primarily occur in the mountainous west and nearly exclusively in the summer.

July 4th also emerged as the most common day for human-induced fires, with over 7,700 total fires started on that day over the two-decade period of the study. The top five reasons behind human-ignited fires: burning debris, arson, equipment use, campfires, and children.

The team suggested national and regional policy initiatives to focus on reducing the human factor in wildfires. They also noted that the wildland-urban interface, or houses that intermingle with natural locations, is anticipated to double by 2030 and will therefore increase fire vulnerability.

For Thomas Swetnam of the University of Arizona, an expert not involved in the study, the “very well done study” detailed not just how people lengthen the fire season but also how climate change primarily drove lightning-caused fire trends in the West.

Balch channeled hopes to reduce human-influenced fires in the medium term and also target more sustainable living in the long term to prevent and control fires.

The findings were discussed in the journal PNAS.

Wildfires happen when certain conditions conducive for a fire are met. A too-dry environment, for example, would not offer enough vegetation to fuel the fire. But researchers believe that due to global warming, there will be more chances for these disasters to occur, and changes that would provide the perfect fire conditions would climb by 35 percent.

And it’s no longer just parts of the United States and Australia that are prone to these events, but also Mediterranean regions that are typically not vulnerable to wildfires.