Deadly wildfires on the edge of Los Angeles are the result of two years of wet conditions, a year of drought and hurricane-force Santa Ana winds, University of Virginia experts said.
Several fires have combined to burn nearly 40,000 acres, destroying thousands of structures and killing at least two dozen people.
The National Weather Service issued red flag warnings and high wind warnings across Southern California on Monday and Tuesday with “particularly dangerous situation” warnings for most of the fire-affected area.
“Dryness is the major factor, and this fire was exacerbated by the winds that are occurring right now,” said Venkataraman Lakshmi, John L. Newcomb Professor of Engineering in UVA’s Department of Civil and Environmental Engineering. “The dry conditions have reduced the vegetation water content and as a result, the vegetation is very susceptible to burning.”
“The two previous years were very wet, with almost double the average annual rainfall. In these water-limited ecosystems, that leads to greater growth, more leaf growth and leaf litter, which desiccates under the hot, dry winds,” Larry Band, UVA’s Ernest Ern Professor of Environmental Science, said.
The Palisades fire, the largest of the four active blazes, began west of Los Angeles and north of Santa Monica. It burned toward Malibu and to the Pacific Ocean, while the Eaton fire burned parts of Pasadena and Altadena. Smaller fires, now mostly contained, also burn in the area.
Little to no rain has fallen in the area since last summer, with late autumn and winter being the usual wet seasons for the region. The National Drought Mitigation Center’s data shows the area around Los Angeles morphed from normal conditions in October to severe drought by Jan. 7. The same source shows this year’s soil moisture content in the region being the dryest since 2015.
Venkataraman Lakshmi, the John L. Newcomb Professor of Engineering in UVA’s Department of Civil and Environmental Engineering, left, and Larry Band, UVA’s Ernest Ern Professor of Environmental Science. (Contributed photos)
The area’s natural vegetation adds to the danger, UVA experts say.
“The native vegetation is chaparral, a family of species that are fire-adapted, burn periodically and resprout. They dominate local ecosystems, as the fires keep out competitors,” Band said. “The chaparral survives the dry, hot Mediterranean climate summers by secreting a resin that coats their leaves, reducing water loss. The resin is very volatile and burns hot.”
Airborne firefighters in a helicopter drop water on the Palisades fire. At least two dozen people have died in wildfires in the Los Angeles metropolitan area. (Photo by Cal Fire)
Band said Santa Ana winds are common in the fall and into early winter, but there is usually some rain during the winter wet season.
“The winds themselves can drop the relative humidity to a few percent, further drying out and making more fire-prone the chaparral and the leaf litter that accumulates on the ground,” Band said.
The combined dry climate and flammable flora have created fires and firestorms before. In October 1978, the Agoura-Malibu and Mulholland Canyon fires burned more than 500 homes and killed three people. The Agoura-Malibu fire grew into a firestorm, a fire so intense it creates its own wind system.
