A week after more than a dozen devastating wildfires erupted across Northern California, the first hopeful news began to emerge that firefighters were getting many blazes under control and some evacuation orders might be lifted.

On Monday the California Department of Forestry and Fire Protection (Cal Fire) reported that 14 large wildfires had destroyed more than 213,000 acres, torched 5,700 structures and taken 41 lives – making it the most deadly week of wildfires in the state’s history.

So what made these fires so severe and what can communities do to protect themselves from future fires?

Perfect Storm of Weather

October is the last, and often the worst, month in California’s fire season as it marks the tail end of the dry season.

“We don’t know what triggered the ignition, but once a fire ignited the real story is that there was receptive vegetation everywhere that could carry that fire,” said Yana Valachovic, a county director and forest adviser for the University of California Division of Agriculture and Natural Resources.

On October 8, when the series of blazes began, there had been a red flag warning, which is an indication from officials of extreme fire danger often prompted by the combination of low humidity, dry vegetation and strong winds.

“We had a north wind, it also brought on low humidity, and things were just right for wildfires and that allowed the fires to grow so rapidly and move toward the homes,” said Jaime Williams, a public information officer with Cal Fire. “That’s why so much devastation occurred. Everything aligned for a perfect storm, if you will.”

While this confluence of factors is not unexpected in October, it was “extreme fire weather,” said Valachovic. And the driving force of the fire was wind that gusted up to 70 miles per hour and pushed embers a mile head of the fire, she said. “It’s a lot like being in a horizontal hailstorm of coals.”

Drought and Management Impacts

Since California endured five years of drought, much attention has been given to the more than 100 million trees that died in the Sierra Nevada and the wildfire risk they pose. But there has been tree mortality in the Coast Range, as well, said Valachovic, which contributed to the 2015 Valley Fire in Northern California’s Lake County.

“We’ve had a lot of vegetation that has been really stressed – some of it has died,” she said. There has been more focus on trees and not as much on dead shrubs and other woody vegetation and accumulated dead materials. “Even though we had a pretty wet winter it takes a while to get all that dead material to decompose. I don’t think it’s helping to have had four or so years of drought,” she added.

It’s not just dry, but also hot. California just finished its hottest summer on record and an increase in both hot and dry conditions is something scientists have said the state is likely to see more of with climate change. And those are conditions that will help drive more severe wildfires.

How California manages its wildlands is also important.

The Tubbs Fire, which swept through suburban Santa Rosa, reducing neighborhoods to ash, seems to have begun from an ignition in grassland area and then moved to scrubby coast woodlands that contain live oak and manzanita, said Valachovic. There are forests where there is “fuel continuity” and fire can move from the ground to the tree canopy.

The density of vegetation may also be a factor in California fires, she said. “The basic message is that the landscapes of California have become much too dense and that has resulted in too many straws sucking out the only available water there is,” she explained. “We need to figure out how to reduce that density and that will have a lot of benefits overall and it should result in more water availability and resilience to wildlife.”

The density of California’s forests and a call for a change in management was the subject of a recent report from the Public Policy Institute of California, which called for more mechanical thinning and prescribed burns to better manage forests for wildfire.

Rethinking the Wildland-Urban Interface

Because of the high winds and dry conditions and the fact that the fires spread quickly during the night, many people had just minutes to try to escape the fires. But under different conditions, where people have hours or days to prepare for a wildfire, there is a lot that can be done to protect homes, said Valachovic.

Leaves in gutters, vegetation close to a house and leaf debris or other flammable material around homes can quickly spread fire as embers are blown in the wind. In this case, with the high velocity of the winds, vents in homes designed to let moisture out likely let embers into homes, which then caused fire to spread from the inside to the outside of the home and then from home to home in more densely settled neighborhoods, Valachovic said. Large shopping centers surrounded by parking lots and not vegetation may have burned because the HVAC systems in those buildings sucked embers inside the buildings, she said.

“Fortunately we don’t always have this fire weather,” she said. “Most fires ignite during more moderate conditions where there is a lot you can do. But if you continue to have susceptible vegetation everywhere it becomes harder to control those fires.”

The aftermath of these fires will likely also have officials rethinking which areas are at risk for wildfire and better strategies for living in the “wildland-urban interface” – areas adjacent to wildlands that are at risk of fire.

One of the most photographed areas of destruction has been Santa Rosa’s Coffey Park neighborhood, where hundreds of houses were obliterated by the fire. And blowing embers, not sweeping flames, is the likely cause, a Los Angeles Times article surmised. The Times reported that the neighborhood was not officially mapped as being an area of high hazard (which was 5 miles away) and therefore wasn’t subject to the same fire-resistant building regulations.

“With a lot of hazard mapping, once you get into a density of development, it’s mapped urban and it’s considered unburnable,” Max Moritz, a fire specialist with the University of California’s Cooperative Extension, told the Times. “From its core, our whole approach to fire behavior modeling, we are not talking about burning in urbanized environments.”

Valachovic said that surrounding homes with a 5ft noncombustible zone can help in many fires, which could include a watered lawn, hard surfaces, gravel, pavers, concrete or more bare earth.

“Landscapes in California are designed to burn and we just happen to be in the way of that,” she said. “And we are heavily building out the wildland-urban interface and that is putting us into more conflict. There is a lot more we need to do in terms of community preparedness, fuels management and managed wildfire – all of it will have to come into play.”