Southern California is bracing for potentially severe weather this week as a strong atmospheric river is expected to hit the region, raising concerns about damaging debris flows. Rainfall is anticipated to begin Wednesday morning, with the most significant impact expected early Thursday and continuing through Thursday night into Friday morning. Meteorologists forecast substantial precipitation, with coastal and valley areas possibly receiving between 2 to 4 inches, while mountains and foothills could see 4 to 8 inches or more.
The National Weather Service has indicated a 60% chance of this intense rainfall occurring in Santa Barbara and San Luis Obispo counties, while Los Angeles and Ventura counties face a 40% chance, an increase from the previous 30% forecast. While this rain could provide relief after a devastating winter fire season, it also poses a serious risk of landslides, a recurring issue for many Californians.
Landslides are particularly threatening in regions close to mountains, where steep terrain can quickly turn heavy rainfall into deadly flows of mud and debris. The unique geography of California, with its tall mountains and rapid elevation changes, exacerbates this risk, especially as development increases in these vulnerable areas.
Wildfires have further heightened the danger. When vegetation is burned away, the soil becomes less stable and more prone to erosion. This loss of plant life means that during heavy rains, water cannot be absorbed effectively and instead runs off, picking up debris and increasing the likelihood of mudslides. Experts note that the first few years following a wildfire are the most critical for landslide risk, with areas remaining susceptible for up to five years as vegetation gradually regrows.
Meteorologists indicate that rainfall rates of half an inch per hour can trigger debris flows in recently burned areas, with higher rates leading to more severe flows. Such conditions can persist even after the rain has stopped, as saturated hillsides may collapse and cause additional hazards.
Recent history underscores the potential for catastrophe. In January 2018, a devastating debris flow in Montecito, which followed the Thomas Fire, resulted in the deaths of 23 people and significant property damage. Similarly, past incidents have demonstrated the destructive power of mudslides, with heavy rains causing landslides in areas that had not recently burned.
As Southern California prepares for this week’s storm, residents are urged to stay informed and take precautions, especially those living in high-risk areas. With the potential for significant rainfall and the accompanying risk of landslides, the community must remain vigilant as the storm approaches.