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2017 was the year of fire in California! As of this writing, catastrophic fires are still raging near Los Angeles and the damage is mounting. Deadly fires are not unique to California; in fact, Australia has a history of particularly devastating fires. And climate change is going to provide all of the ingredients for more fires in the future: more fuel, more effective ignition, as well as the conditions to keep fires burning. If you thought that the fall of 2017 was an apocalypse, wait for the future!

Box Canyon Fire
Box Canyon Fire 2017
Credit: Flickr, IvyMike [CC BY 2.0] (Creative Commons)
Fire in Northern California
Fire in Northern California, October 2017

In October 2017, fires spread across several Northern California counties just north of San Francisco, including the famous wine country in Napa and Sonoma. There were 250 fires that raged for days in very dry and windy conditions. These fires charred some 245,000 acres, caused the evacuation of 90,000 people and led to 44 fatalities. A total of 8900 structures and $8 billion in property were lost.

Fire damage in Santa Rosa
Santa Rosa fire damage
Credit: Flickr, California National Guard [CC BY 2.0] (Creative Commons)
Fire damage Sanata Rosa
Fire damage Santa Rosa
Credit: Theresa Havton, UCLA Medical School

Moving on to December 2017, fires extended from Santa Barbara north of Los Angeles to just north of San Diego to its south. A single burn, the Thomas fire is now larger than New York City and Boston combined! The large blazes in southern California have consumed more than 300,000 acres, destroyed over 1000 buildings and led to more than $2 billion if property loss.

The 2017 fire season in California was the worst on record, however, these are not the most devastating fires in Earth’s recent past. Black Saturday Bushfires in February 2009 in Victoria, Australia were fueled by extraordinary heat and strong winds. At the peak of the inferno, there were some 400 blazes. Conditions leading up to the fires were extraordinary. Mercury hit 116 degrees in Melbourne in a heat wave that started the week before the fire, and in the peak of the summer drought, the dry brush was perfect fuel. On the fateful Saturday, the first fire was started by arson. Falling power lines and lightning ignited other fires. Fires consumed some 1.1 million acres, destroyed whole towns, caused some $4.4 billion in damage, and killed 173 people. Most of the damage was done in the first few days, but the blazes raged for weeks. One of the astounding aspects of the fires were observations by firefighters of sideways mini tornadoes, technically called horizontal convective rolls. As the air at the surface warmed and rose, it was forced to move in a corkscrew pattern oriented parallel to the ground. This created bands of alternating fast and slower surface winds. Fast winds surpassed 30 mph and ignited huge swaths of land in a catastrophic fire. There are terrifying stories of people getting swept up in the flames trying to escape the inferno on tiny mountain roads.

Fire on the 405 freeway near UCLA
Fire on the 405 freeway, near UCLA
Credit: An Yin

So how is increased fire activity related to climate change? Fire is very much a part of the ecosystem in places like Australia, California, South Africa, and Southern Europe. Even before people were around, fires ignited by lightning occur regularly in environments with dry seasons, as nature’s way of germinating drought-resistant species and fertilizing the soil. But people have made fire events much more common. First, many fires are started by arson. Clearly, heat and drought are good for fire, and as we have seen, both of these ingredients will increase in the future as a result of anthropogenic climate change. But the other key aspect of fire is fuel and that is supplied by precipitation and active growth of vegetation. Climate change is likely to cause more variability in temperature and precipitation that will create more contrast between drought and wet years. This will lead to greater fire risk. The heavy rains in California in the winter of 2016-2017 caused significant growth of vegetation in uncultivated hills and canyons surrounding residential areas and this dried out in the hot and dry 2017 summer. Then, once the warm fall Santa Ana winds arrived, the recipe for disaster was all ready.

There has been significant debate about how to lessen the impact of fire in the future. Clearing of brush in populated areas has led to the establishment of invasive plant species that grow very rapidly and provide fuel when they die back in the dry season. So many communities are replanting native plant species and using animals to clear out areas overwhelmed by invasives. Controlled burns are a highly effective way of reducing long-term fire risk. But sadly, highly destructive wildfires are part of California’s future.

As are mudslides. The huge Thomas fire destroyed so much vegetation that held hillslopes in place. They were followed in early January by major rains that led to torrents of mud from hills into valleys. The catastrophic mudslides killed at least 20 people and caused massive property damage. Fire and mud are intricately related.

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Homes and streets of a neighborhood affected by the Santa Barbara County mudslides in Santa Barbara, California, Jan. 9, 2018.
Credit: U.S. Coast Guard