There's a lot of data on this subject. BuzzFeed News recently had an article about how fires have changed over the past decades: https://www.buzzfeednews.com/article/peteraldhous/california...

And for the HackerNews-y type, they even made all the data and R code for the visualizations publicly available: https://buzzfeednews.github.io/2018-07-wildfire-trends/

It is hard to pin the increase on any one cause - it's a confluence of factors. Here's a perspective piece by a few well regarded experts: https://www.theguardian.com/environment/2018/aug/07/californ...

One of those experts is Daniel Swain, who has an excellent Twitter account which posts a lot more data: https://twitter.com/Weather_West

If we're talking climate change, you'd need to go back tens of thousands / millions of years to see if recent fires are out of the norm, with recent being defined as 10,000 years or so.