Comparing 1970s-2000 to 2000-2016, the fire season of the latter is 17 days longer, and the window for highest risk of severe fire 9 days longer.
Earlier snowmelt also contributes, especially in combination with a longer warm season.
So, even though we can expect that more large fire is likely due to our legacy of forest management practices, forest aridity is a key driving factor of fire and it has increased substantially over the past decades.
climate change has increased the aridity of forests, the probability of fire, the probability of severe fire, and in many places, decreased the probability of tree regeneration post-fire. And a lot of research supports this.