When hurricane-force winds whipped through Los Angeles County in early January 2025, the hills had ample fuels available to feed a wildland fire. Back-to-back wet years in California led to grasses and chaparral accumulating in the mountains and foothills. Then, warm, dry weather in Los Angeles during the last eight months of 2024 left the vegetation primed to burn.
On January 7, blazes spread quickly in the hills of Pacific Palisades and Eaton Canyon. Santa Ana winds pushed the fires down hills and into neighborhoods, and the two fires eventually covered 37,000 acres (150 square kilometers). Most of the fire spread in the first day after ignition, a characteristic of “fast fires.” These destructive events are usually propelled by strong winds and burn in the autumn or winter when fuels are exceptionally dry.
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).
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.
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.
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.
“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. Story by Emily Cassidy.
