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Source: https://outdoors.stackexchange.com/q/20386
License name: CC BY-SA 3.0
License URL: https://creativecommons.org/licenses/by-sa/3.0/

<p>Forest fires seem to be more numerous and larger, and the forest fire season is getting longer.  Some of these fires are caused by arson.  For example, from <a href="https://www.usatoday.com/story/news/2018/08/09/arson-charges-against-suspect-californias-holy-fire/948126002/" rel="noreferrer">USA Today</a>: </p>

<blockquote>
  <p>The man suspected of igniting the Holy Fire in Southern California was
  charged on Thursday with three counts of felony arson, among other
  offenses.</p>
</blockquote>

<p>The Carr Fire, another large 2018 fire, was caused accidentally by a spark from a motor vehicle.  According to <a href="https://www.cnn.com/2018/08/04/us/carr-fire-week-wrap/index.html" rel="noreferrer">CNN</a>:</p>

<blockquote>
  <p>... on one road near Redding, California, when a tire failed last
  month on a trailer and its rim scraped the asphalt, the result was
  catastrophic for an entire region.</p>
  
  <p>The sparks that shot out July 23 from that minor incident, California
  fire officials said, ignited what is now the sixth-most destructive
  wildfire in state history.</p>
</blockquote>

<p>Improperly attended campfires have caused major forest fires, although my limited search did not turn up a campfire as the cause of a major forest fire in 2018.  </p>

<p><strong>In the past few years, what have been the immediate causes of major forest fires in the US and Canada?  Suggested breakout: arson, vehicles, campfires, other human causes, lightning, other natural causes (if any). Canada and the US should probably be listed separately.</strong>  </p>

<p>"Several years" is intentionally vague; it depends on what data is available.  Let's say several years means two to ten.  "Major forest fires" is also vague.  I suggest Class F and Class G fires, or perhaps just Class G fires, as defined by <a href="https://www.nwcg.gov/term/glossary/size-class-of-fire%C2%A0" rel="noreferrer">The National Wildfire Coordinating Group</a>:</p>

<blockquote>
  <p>◦Class E - 300 acres or more, but less than 1,000 acres;</p>
  
  <p>◦Class F - 1,000 acres or more, but less than 5,000 acres;</p>
  
  <p>◦Class G - 5,000 acres or more**</p>
</blockquote>

<p>If someone has a better definition for a major fire, please use it.</p>

<p>Note that I am not asking about what may be the ultimate causes such as climate change or fire management policies.     </p>