A perfect storm of climate extremes set the stage for devastating wildfires in Los Angeles in early 2025.
After two consecutive wet years fueled lush plant growth, an extended eight-month dry spell turned the landscape into a tinderbox. When powerful Santa Ana winds swept through, fast-moving blazes tore across 37,000 acres, consuming neighborhoods and hillsides.
Fires Fueled by Extreme Weather Shifts
In early January 2025, hurricane-force winds swept through Los Angeles County, where an abundance of dry vegetation provided ample fuel for wildfires. The previous two years had been unusually wet, allowing grasses and chaparral to flourish in the region’s mountains and foothills. However, the last eight months of 2024 brought warm, dry conditions that turned this growth into highly flammable fuel.
On January 7, wildfires ignited in the hills of Pacific Palisades and Eaton Canyon, spreading rapidly. Strong Santa Ana winds pushed the flames downhill into residential areas, and the two fires quickly expanded, burning 37,000 acres (150 square kilometers). Most of the damage occurred within the first 24 hours, a hallmark of “fast fires” — intense, wind-driven blazes that typically erupt in autumn or winter when vegetation is extremely dry.
The Role of Hydroclimate Whiplash
Researchers at the University of California, Los Angeles (UCLA) noted that several factors contributed to the severity of the fires, including a buildup of vegetation between 2022 and into 2024, followed by very warm and dry conditions in summer 2024. The rapid swing from wet to dry—dubbed “hydroclimate whiplash”—can amplify the risk of wildland fires and has become more common in the 21st century.
From 2022 to early 2024, Southern California received above-average precipitation, said Gavin Madakumbura, a postdoctoral researcher at UCLA. The 2022-2023 water year, which runs from October through September, saw unrelenting atmospheric rivers that delivered torrential rain to California. Much of the 2023-2024 water year was also wet, and rainfall totals for both periods, measured in downtown LA, were nearly twice the long-term average (1877-2024).
Vegetation Growth and Fire Risks
The ample rain allowed vegetation to build up, which is apparent in the map above. It shows a satellite-based index of plant health, or “greenness,” over the meteorological summer before the fires. This metric, known as the Normalized Difference Vegetation Index (NDVI), is based on data collected by the Landsat satellites.
The map indicates that many parts of Los Angeles County were 30 percent greener than average in summer 2024 (compared to a record from 1991 to 2020). That July, the National Interagency Fire Center warned that “herbaceous fuel loadings” were above normal throughout California, and in some hilly areas, were twice the normal amount.
A Sudden Shift to Extreme Dryness
Conditions shifted in the last half of 2024. According to Madakumbura and colleagues, the Los Angeles region received no significant rain between May 2024 and early January 2025, which dried out the accumulated vegetation. On January 4, 2025, the Los Angeles Times reported that the downtown area had only one instance in the previous eight months when rainfall exceeded a tenth of an inch—the threshold considered helpful for reducing wildfire risk by keeping plants from drying out. That made it the second-driest May to January on a record that goes back to 1877.
The landscape’s dryness was made worse by heatwaves that struck the U.S. Southwest in June and July 2024, either breaking or tying temperature records in several cities in California.
Unprecedented Dry Soil Conditions
The map above shows moisture relative to normal in the top 40 inches (100 centimeters) of soil, in the “root zone,” on January 7, 2025, the day the Palisades and Eaton fires ignited. The data are from NASA’s SPoRT (Short-term Prediction Research and Transition) Center at Marshall Space Flight Center. The soil moisture in much of Southern California was in the bottom 2 percent of historical records (1981-2013) for that day.
Tracking Fire Risk with NASA Data
“This is historically low soil moisture,” said Jonathan Case, a meteorologist with NASA SPoRT who has studied how moisture conditions can contribute to fire risk.
SPoRT’s Land Information System (SPoRT-LIS) provides 3-kilometer resolution gridded soil moisture products in near real-time to support regional and local modeling and is used by the U.S. Drought Monitor to track drought conditions across the country.
NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey and soil moisture data from NASA’s Short-term Prediction Research and Transition (SPoRT) Center.
