A lot of it is fuel, though that's increasing due to both a century of near-total suppression, which began around 1910-1920, with an "out by 10" policy -- the idea that any fire should be completely suppressed by 10am -- explicitly stated by 1935:
- Human factors: encroachment on the wilderness interface, ignition sources, building codes, transport routes, etc., effect both frequency and impacts. Many fires are of natural origin, thought that's only about 15%. How much that percentage has changed since 1930 I don't know.
NB: general information and perceptions, though they should stand up.
That's similar to a long conversation I'd had with a retired forestry worker in 2007. Chance encounter on a road trip, he talked about the idiocy of total suppression policy at the time. Unfortunately, not citable, though it was a very memorable discussion.
