Deadly and destructive fires are sweeping through the Los Angeles areaand strong winds literally fan the fire.
By Wednesday afternoon, four fast-moving fires had killed two people, injured many and destroyed more than 1,000 structures, while threatening another 28,000 and forcing at least 70,000 people to evacuate.
Here’s how winds make wildfires more dangerous and harder to fight.
What kind of winds are they and why are they so strong?
Santa Ana winds are strong winds that blow from dry inland areas toward the coast, mostly in the colder months, for several days to a week.
The National Weather Service says Santa Ana’s winds reached 129 km/h in some areas around LA early Wednesday, and could reach 160 km/h in the mountains and foothills.
Wind gusts of up to 95 km/h are expected through Thursday, the LA County Fire Department said Wednesday.
These winds come from the dry desert regions of Nevada, Utah, Idaho, and southeastern Oregon, and become even drier as they descend the mountains.
Peter Mullinax, a meteorologist with the weather service’s office in College Park, Md., called what the region is experiencing “extremely critical fire weather,” due to a combination of strong winds on the highest terrain and extremely low humidity.
The mountain fire, which broke out earlier this week in California’s Ventura County, has spread to more than 80 square kilometers and required the evacuation of about 10,000 people.
How does wind affect the spread of fire?
The faster the winds, the faster the fire spreads. Rule of thumb used by wildland firefighters is that fires spread 10 percent faster than the 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 for this.
- Wind helps supply the fire with air and oxygen.
- It also flattens and bends the flame towards the dead wood and other fuel in front. This can preheat and blow sparks and embers into these new, dry fuel sources, causing spot fires.
- The direction of the wind is what most determines the direction of fire spread, according to the National Meteorological Service.
- Wind also dries vegetation, turning it into more flammable fuel.
Lindon Pronto, senior fire management expert at the European Fire Institute, said the Santa Ana winds’ ability to dry vegetation to its lowest moisture content of the year was one of its “really dangerous effects”.
“The fuel itself becomes extremely accessible to the fire and can engulf and spread the fire very quickly,” he told Reuters.
This increases fire risk and worsens fire conditions already caused by climate change.
Sylvia Dee, an assistant professor and climate scientist at Rice University in Houston, said climate change has created increasingly hot and drier conditions across the region, “and that creates a kind of fire box.”
How does this affect firefighting efforts?
As of midday Wednesday, 1,400 firefighters were on the ground, but aerial efforts were hampered by the fact that it was too windy for firefighting aircraft to fly, the Associated Press reported.
Winds can cause turbulence, especially in mountainous terrain, or even damage the aircraft if they are too strong.
