Basically, because it has a wet season and a dry season, not because of climate change.
The wet season, which begins in October, is marked by storms coming in from the west and northwest. The hills slowly become a velvety green.
Most of the vegetation dies off in the dry season, which begins in May. The hills become golden brown, dotted in some areas by Oaks, Redwoods and Pines.
Next, consider the fire triangle. A fire needs fuel, oxygen and an ignition source.
Oxygen is always available, unless you’re living on Mars. As for the fuel, see the remarks above about the dry season. Here is Mt. Poop on 05/26/18, barely visible, surrounded by wild oat in its final days, five to six feet tall (for a recent view of the same area, see this video).
The wet season ending in 2017 brought twice the normal amount of rain. There was a population explosion of everything. Small animals running all over the ranch that had never been seen before (or since). The ground was pockmarked with their holes.
Vegetation died off, leaving many seeds.
The wet season ending in 2018 accrued much less precipitation than the previous year until March, which saw rain almost every day.
Here is another photo from 05/26/18. This is the fuel.
Dead and dying chaparral add to the mix (photo dated 11/24/18).
Ignition sources include, but are not limited to, lightning, camp fires, power lines, cigarettes, off-road vehicles and trailers with safety chains dragging on the road.
Prompted by fires in 2017, Pacific Gas and Electric Company came up will a brilliant idea: shut off power to those at risk. Rural customers, on private water systems, would lose their ability to fight fires unless they had backup generators. (This was not done ahead of the Camp Fire.)
Having spent the summer and fall knocking down dead grass, I can tell you it was very thick and heavy this year. The effort stalled on 11/22/18, after receiving the first appreciable rainfall of the new wet season. Photo taken 11/24/18.
If you move the piles aside, you’ll see new sprouts (photo dated 11/24/18).
The 2019 wildfire season is now getting started, whether you’re ready for it or not.