A powerful rainstorm moving down the California coast could dump more than an inch of rain over multiple burn scar areas in Los Angeles County today, including those of the Eaton and Palisades fires. County officials have issued evacuation warnings and orders for these areas due to the risk of flash flooding, mudslides, and debris flows.
The storm, which started in the Pacific Northwest, brought heavy rain to parts of Southern California late Monday night. National Weather Service forecasters expect it to continue impacting the region through Tuesday. The coasts and valleys could see rainfall totals of up to 1.50 inches (3.8 centimeters), while the foothills and mountains receive up to 4 inches (10 cm).
The risk of flooding, mudslides, and debris flows is especially high in and below burn scars—areas charred by recent wildfires. In January, the devastating Eaton and Palisades fires consumed nearly 40,000 acres (16,000 hectares) in LA County.
“As today’s storm intensifies, I cannot emphasize strongly enough the importance of heeding evacuation warnings and orders,” LA County Board of Supervisors Chair Kathryn Barger said in a statement. “These alerts are issued to protect lives. Conditions can change quickly, and once debris flows begin, it may be too late for emergency crews to reach you.”
How wildfire elevates flood risk
Burned soil can be as water-repellant as pavement, according to the NWS. As plants burn, they release a waxy substance that melts and solidifies on the top layer of soil, causing it to become hydrophobic. At the same time, fire also burns plant stems and leaves that slow rainwater’s contact with the ground, as well as roots that stabilize the soil.
As a result, it takes much less rainfall to produce a flash flood, debris flow, or mudslide in a burn scar than in an area unaffected by wildfire. A good rule of thumb is: If you can look uphill from where you are and see a burnt-out area, you are at risk, the NWS states.
The Eaton fire burn scar stretches some 14,000 acres (5,600 hectares) across Altadena and Pasadena, while the Palisades fire scar encompasses nearly 24,000 acres (9,700 hectares) in and around the Pacific Palisades and Malibu. Other areas that could see significant impacts from today’s storm include the Hawk, Hurst, Kenneth, Sunset, Lidia, Bridge, Canyon, Hughes, and Franklin burn areas, according to LA County.
Compounding catastrophes
Officials expect these wildfire-affected areas to experience moderate debris flows and mudflows, with the potential for some streets to become completely blocked by debris. This may also endanger some structures depending on the location and terrain.
Exactly how this storm will affect communities in burn scar areas remains to be seen, but the risks underscore the lasting impact of wildfire on the landscape and public safety. Californians have become well acquainted with this phenomenon in recent years. Just last week, remnants of Hurricane Priscilla triggered flooding and debris flows in Pine Valley, which was impacted by the Forsyth fire in June.
As climate change increases the frequency and severity of both wildfires and rainstorms, their compounding impacts will only escalate. This is already straining emergency resources in California and the Pacific Northwest, with no real solution in sight as global temperatures continue to rise.