"The model is basically trying to describe areas and their likelihood for a structure to ignite," Dave Sapsis, a Cal Fire researcher who specializes in mapping and research models, told KQED in 2019. "How likely is the fire? And what is the nature of the fire?"
Sapsis says it's important to remember that the Cal Fire-defined risk zones are showing only a probability.
"Estimating a burn probability is an estimate. It's like estimating the weather. We do the best we can based on the tools we have," he says.
And, as recent fires have tragically demonstrated, living outside a higher-risk zone doesn't mean that you're safe.
Extreme winds drove much of the damage in Paradise during last the November 2018 Camp Fire and in the North Bay during the October 2017 fire siege, and current fire maps don't take that factor into account.
(Cal Fire was expected to release new draft maps to test in winter 2019/2020 that took new risk factors into account. So far, they have not been made public.)
Original 2019 story continues below
New Maps to Assess Weather and Development
Sapsis says that fire modeling technology is improving all the time, and that the new models Cal Fire is testing are taking into account dry, windy weather.
"We're just now getting the capacity to estimate at a realistic scale what these areas, footprints, if you will, of these dry windy events are ... and what the magnitudes of these events are," Sapsis says.
Those kinds of weather conditions are tricky to map, Sapsis says, because you want to take into account those very destructive types of fires, but also need to consider a longer, 50-year period.
Fire “hazard” is a measure of how a fire will behave, based on the physical conditions. But the risk, or how much damage a fire can do, depends on the built environment.
The new maps are meant to show "where fires could go," not where they could start, Sapsis says.
For instance, development patterns can change how fire spreads. In urban areas, fires can move quickly through dense neighborhoods where homes are tightly spaced.
"You don't want to zone that house based on what's there, but what could potentially be there," Sapsis says.
Cal Fire hopes to start testing its new draft maps this winter. The agency expects to release official maps next summer for "state responsibility areas" -- the parts of California areas that it's responsible for protecting. After that, Cal Fire will work with local governments to develop new maps for those areas, too.
Note: KQED has simplified these maps for online display. For more detail, please see Cal Fire's official county maps for both state and local responsibility areas.