Southern California state officials issued a flash flood warning on Sunday—the most severe flood advisory—for Malibu, the Palisades, and Los Angeles County.

Still reeling from a wave of wildfires over the past two weeks, the region now faces a heightened risk of life-threatening damage to homes and vehicles, with the added danger of mudslides.

The storm disrupted Southern California’s extended dry spell. Before the weekend, downtown L.A. had recorded just 0.16 inches of rainfall since October. Then, on Saturday evening alone, it saw 0.11 inches, nearly two-thirds of what had accumulated over the previous three months.

Jack Dvorsky takes a photo of his parents, Miriam and Daniel Dvorsky, as they take a break from sifting through the burned ruins of their family home, in Los Angeles, California, U.S., January 24, 2025. REUTERS/Ann Saphir

The areas most affected by recent fires are particularly vulnerable to flash floods for a few key reasons. Under normal conditions, vegetation helps absorb rainwater, reducing the risk of flooding. However, when wildfires strip away plant life, the exposed soil forms a water-resistant layer due to accumulated ash and debris. Instead of being absorbed, rainwater runs off the surface, increasing the likelihood of flash floods—even with relatively modest rainfall.

Despite intermittent rain, much of Southern California remains in a state of severe to extreme drought, according to the U.S. Drought Monitor.

To understand the potential severity of flash floods, one needs only look at history. The worst U.S. flash flood occurred in Davenport, Iowa, a city already prone to flooding due to its location along the Mississippi River. With no floodwalls or levees in place, Davenport was left vulnerable. On August 1, 1993, after a powerful storm, the river crested at a staggering 22.63 feet (6.90 m). Highways and infrastructure suffered extensive damage and four people died. The event later became known as the “Great Flood of 1993.”

Southern California flood warning

The Des Moines Water Works plant is surrounded by flood waters, Friday, July 16, 1993, Des Moines, Iowa. The plant has been contaminated and unable to supply water to the city for six days. (AP Photo/Jeff Davis)

For Southern California, the flood risk isn’t going away anytime soon. Experts predict heightened vulnerability for the next two to five years, depending on local vegetation’s recovery and ability to help regulate rainfall absorption. In the meantime, residents must remain vigilant, particularly during thunderstorms, and be aware of the looming threat of mudslides, which can carry debris, destroy property, and pose serious safety hazards.