Heavy Rain Raises Risks of Flooding Across California Burn Scars

Local officials in Southern California are warning residents that they should prepare for flooding as heavy rain continues to inundate the region. Evacuation warnings have already been issued in some parts of southern California as the threat increases. Here is a look at what is happening in the Golden State.

Burn Scar Areas Vulnerable to Flash Flooding Through End of Week

While there is no doubt that California could use the moisture, an atmospheric river that has set up over the West Coast is causing its own set of issues. The concern for flooding is the most pronounced in recent burn scar areas, particularly in communities such as Palisades and Altadena due to their steep slopes. The flooding could serve as a double whammy for a part of the country still reeling after January's deadly wildfires.

The heavy rain will raise the threat of flash flooding, mudslides, and debris flows throughout the wildfire-ravaged areas of Southern California. Debris flows can carry a number of hazardous elements, including rocks, trees, mud, vehicles, and even structures. Toxic runoff is another concern if the water picks up the leftover chemicals and other irritants left behind by the fires.

It has been a relatively docile wet season for California up until this week. Metro areas such as Los Angeles have picked up little to no rain until now despite this being the time of the year when the region sees the bulk of its moisture. The ongoing drought conditions were largely to blame for the historic wildfires last month.

Understanding the Dangers of Burn Scars

The Palisades Fire and the Eaton Fire left behind massive burn scars. As a fire rips through an area, it brings down trees and vegetation, leaving large "scars" of barren land. Areas that were once rich with full trees and bushes have been reduced to dry soil and ashes.

The lack of vegetation poses its own set of threats when the rainy season kicks in. The lack of trees and vegetation caused by a fire can often leave an area vulnerable to other threats, especially when the rainy season begins. It is important to remember that burned earth behaves more like concrete or pavement rather than soil. Any rain that falls across these scars can raise the chances of flash flooding, debris flows, and mudslides.

Because so many of these burn scars are still littered with burned materials and chemicals, too much rain can also send dangerous runoff into populated areas. This toxic runoff can make its way down to the area beaches.

Wildfire activity can also change the overall composition of the soil. The soil is not able to absorb moisture as easily, causing it to behave as a repellent. This means that even light to moderate rainfall amounts can generate a torrent of flooding. Soil damage is severe enough in some places burned by January's fires that it could take several years for the vegetation to grow back.

The first major rain event that moved through Southern California after the historic wildfires caused several mudslides. Forecasters are warning that this week's rain will be even heavier, resulting in a greater threat of mudslides, landslides, and toxic flows.

In addition to the normal complications caused by flooding, the force of the roaring water and debris can damage vulnerable infrastructure in its path. The fires damaged a multitude of roadways, bridges, and buildings. It will not take a forceful flow of water to bring down some of these structures.

Residents are being asked to prepare for the persistent rain. Free sandbags have been available to members of the public at many of the area fire stations. The U.S. Army Corps of Engineers is also on the scene working alongside the Los Angeles County Department of Public Works to clear up the leftover debris from the fires.

Officials have also installed concrete barriers in some vulnerable areas to guard against the flooding impacts. Sandbags have also been placed around storm drains to keep them from being clogged with flowing debris. Search-and-rescue teams are also on standby to assist with the evacuation process if needed.

Looking at the Forecast