Fires are deadly and destructive making their way through the Los Angeles areaand powerful winds literally fan the flames.
By Wednesday afternoon, four rapidly spreading fires had killed two people, injured many more and destroyed more than 1,000 structures, while endangering 28,000 more and forcing at least 70,000 people to evacuate.
Here's how winds make wildfires more dangerous and harder to fight.
What types of winds are these and why are they so strong?
Santa Ana winds are strong winds that blow from dry areas inland towards the coast, usually in the colder months, for several days to a week.
The National Weather Service says Santa Ana wind speeds reached 70 mph in some areas of Los Angeles early Wednesday and could reach 100 mph in the mountains and foothills.
As the Los Angeles County Fire Department reported on Wednesday, wind gusts of up to 95 km/h are expected through Thursday.
These winds originate in the dry desert regions of Nevada, Utah, Idaho, and southeastern Oregon, and become even drier as they descend from the mountains.
Peter Mullinax, a meteorologist with the weather office in College Park, Maryland, called what the region is experiencing “extremely critical fire weather conditions” caused by a combination of strong wind gusts in the highest areas and extremely low humidity.
A mountain fire that broke out earlier this week in California's Ventura County has grown to more than 80 square kilometers and forced the evacuation of about 10,000 people.
How does wind affect the spread of fire?
The faster the wind, the faster the fire spreads. Rule of thumb used by firefighters from green areas is that fires spread at 10 percent of wind speed. For example, a wind speed of 25 km/h would allow a fire to spread at a speed of 2.5 km/h.
There are several reasons.
- The wind helps supply the fire with air and oxygen.
- It also flattens and bends the flames towards the dead wood and other fuel in front of you. This can preheat and blow sparks and embers into new, dry fuel sources, causing spot fires.
- The National Weather Service says wind direction largely determines the direction of fire spread.
- Wind also dries out vegetation, turning it into more flammable fuel.
Lindon Pronto, senior fire management expert at the European Fire Institute, said the ability of Santa Ana winds to dry vegetation to the lowest humidity of the year is one of their “really dangerous effects.”
“The fuel itself becomes extremely flammable and can catch fire and spread fire very quickly,” he told Reuters.
This increases fire risk and worse fire conditions that are already caused by climate change.
Sylvia Dee, an assistant professor and climate scientist at Rice University in Houston, said climate change has made the region generally warmer and drier, “and that creates kind of a powder keg.”
What impact does this have on firefighters' actions?
By noon Wednesday, 1,400 firefighters were on the ground, but air operations were hampered by the fact that it was too windy for firefighting planes to fly, the Associated Press reported.
Winds can generate turbulence, especially in mountainous areas, and even damage aircraft if they are too intense.