Sustained heat, lack of rain, abundant fuels.
When I think of hazards and California, my mind used to primarily go to earthquakes. Well, the last significant earthquake was 1994 Northridge.
Since then there has been a drought of earthquakes and more recently rain in California. They did have a good year of rain/storms last year, but with record heat waves, it does not take much to be brought directly back to extremely dry conditions.
Thus, today when people think of California and disasters, they are more likely to think of wildland fires and those that are now entering the wildland interface where urbanization and the wild meet.
See this article, Why are California's wildfires so intense and what can be done?
Note, these are usually not forested areas. Clear cutting is not the solution and while carbon might have created the problems we are having today and may worsen them more in the future, we will likely have to fall back on climate adaptation strategies for prevention. Separating people and the built environment from the hazard. Employing more fire-resistant materials in our building practices, and other such measures are the practical steps we can start taking today.
And, don't forget the fire insurance! I expect premiums will start going up for everyone — to pay for losses, and they should go up for structures that exist in more fire hazard areas. People won't like it — but they made choices when they bought homes or built homes where they did.
I shared last year that my son-in-law's parents lost their home to a forest fire in Montana. Fires had come close many times in the past, but this time it consumed their home of many years. Living in the wild/forest is a choice, and as I told my children growing up, with choices sometimes come consequences.
Claire Rubin shared the fire link above.