Here are some basics on the California wildfires from my perspective as a forest fire researcher. This won't be the blow-by-blow I would do under different circumstances, but just some basics that folks seem to be asking me that I can provide.

The fires themselves seem to be winding down. According to the report I am reading (linked above), they displaced 640,000 people, destroyed 1800 homes, and burned over 200,000 ha over 23 fires, and done over $1 billion USD worth of damage.

By Ontario standards, this is a great deal of fire. Over the past 30 years, the median area burned was about 150,000 ha, for Ontario.

California is about 400,000 square kilometres and Ontario is about 900,000 square kilometres in size. So this was both a huge amount of area burned and a larger percentage of California's area that was burned.

Forest fires occur when three elements come together: fuel, weather, and ignition. The key element in large fires such as the ones we've seen in California is weather. If the weather is hot and dry and winds are high, it is basically impossible to stop a fire.

Fire suppression crews in this context can try to ignite backfires or built fire breaks, but in hot, dry weather with high winds, the problem of 'spotting' is serious. 'Spotting' occurs when firebrands are thrown up from the burning vegetation, carried by the wind, and land in unburned forests, becoming ignition sources for new fires. Because of 'spotting', fires can 'jump' even large firebreaks.

The other issue in the California wildfires is what is called the 'wildland urban interface'. This is another fuel issue. There are aesthetic, spiritual, and cultural reasons to want homes surrounded by forests, but this can create 'fuel continuity', so that a fire can spread through the forest up to the house. Some 'fireproofing' can be done by including firebreaks and considerable distance between the building and the forest. How much of a difference these sorts of firebreaks can make is the subject of ongoing research.

The ignition does matter, as do issues like fuel buildup, in some forests (whether fuel buildup matters in Ontario's boreal forest is debated in the scientific community, but in California's forests it is generally accepted to be a factor). The key factor in these large fires is weather. With global warming, we can expect to see more large fires.