Landslides and Debris Flows
Climate change is expected to increase the frequency of debris flows, or fast-moving landslides or mudslides, on the slopes of San Mateo County as storms and fires become more frequent. As many South Coast and Southern San Mateo County residents learned after the 2021 CZU fires, areas with wildfire burn scars are at higher risk for debris flows during storms. Storms can also increase debris flow risk, especially when soils are already saturated. During the Winter storms of 2022-23, many landslides and debris flows occurred that cut off major roads including Highway 92. These events can occur suddenly, and debris can flow for miles and result in extensive damage.
Areas that have experienced debris flows and landslides in the past may be more likely to experience them again, especially with the increase in extreme precipitation events projected.
Rapidly moving debris and landslides can injure people, disrupt utilities, damage homes and other buildings, and block transportation corridors and transit rails, impacting both commuters and people who need to evacuate. They pose an acute threat to the safety of those who live or who are using roadways below them. The placement of roads in valleys or along the sides of slopes and roads themselves can destabilize slopes over the long term.
Members of socially vulnerable and low-income communities may have fewer resources to recover in the aftermath of debris flows. Renters can have limited control over whether or when their housing may be repaired or rebuilt. Socially vulnerable communities can be more likely to experience challenges during disasters, especially if they also lack access to transportation, lack access to cell phone or internet service, or face language barriers.
