Preparing for Mudslides and Debris Flows Ahead of Extreme Weather


Extreme weather with heightened rainfall and potential flooding across California may bring about mudslides and debris flows. Because of this, the California Governor’s Office of Emergency Services (Cal OES) underscores the critical importance of thorough preparation.  

Unpredictable and severe weather conditions may occur and Californians are urged to be informed and prepared to effectively navigate the challenges that can accompany this weather phenomenon.  


Mudslide and debris flow events, often triggered by heavy rainfall and subsequent soil saturation, are characterized by the rapid downhill movement of soil, rocks and other debris. Understanding the intricacies and triggers of mudslides and debris flows is essential for communities situated in regions prone to these occurrences.  

In the United States, landslides and debris flows result in 25 to 50 deaths each year. The health hazards associated with landslides and mudflows include: 

  • Rapidly moving water and debris that can lead to trauma 
  • Broken electrical, water, gas and sewage lines that can result in injury or illness 
  • Disrupted roadways and railways that can endanger motorists and disrupt transport and access to health care. 


  • Mudslides: a type of landslide that result from the failure of a slope, and often occurs due to the accumulation of water from prolonged rainfall and/or saturated subsurface conditions.  
  • Debris Flows: described as a “sediment-dominated slurry,” debris flows are mostly made up of soil, resulting from short-duration, high-intensity rainfall events.  
  • A mudslide is a localized slope failure, while a debris flow is a runoff event, such as a flash flood, that entrains sediment from a broad area.  
  • Debris flows and mudslides can occur many years after wildfires. Both happen fast, so heed evacuation warnings immediately 


A critical aspect of preparedness involves a comprehensive understanding of the specific hazards associated with mudslides and debris flows. Californians should be aware of the geographical and environmental factors contributing to these events in their region. This knowledge enables individuals to make informed decisions about where to live, work, and recreate, considering the potential risks posed by natural hazards. 

To check your hazards, visit:  

Where intense wildfires occur, soils can develop a layer that repels water, like rain on pavement, due to the charred remnants of organic material. Rainfall that would normally be absorbed by the soil will instead quickly run off.  

Consequently, much less precipitation is required to produce a flash flood, and the potential for mudslides and debris flows increases with the loss of organic material that holds the soil in place. Because of this, locations that are downhill and downstream from burned areas are highly vulnerable to rain that can cause mudslides and debris flows, especially in and around steep terrain. 


Understanding environmental warning signs indicating an area may be at high risk of mudslides and debris flows is crucial for swift and effective response.  

Californians should educate themselves on environmental indicators such as: 

  • Increased slope erosion (look for new sediment deposits at the bottom of slopes) 
  • Presence of large boulders on the landscape may indicate previous high-flow events 
  • Proximity to burned watersheds 
  • Increased runoff due to prolonged drought conditions 

Recognizing these environmental indicators empowers individuals to take prompt actions to safeguard themselves, their families and their property. 


Staying informed is a cornerstone of disaster preparedness. Californians are urged to register for local emergency alerts to receive timely and accurate information about potential mudslides and debris flows in their area. This proactive step ensures that individuals can respond promptly to evolving situations, follow official guidance and evacuate to safer locations in a timely manner. 


High intensity rainfall events are the triggering force for a debris flow event. Given the dynamic nature of weather conditions leading to mudslides and debris flows, Californians in high-risk areas should monitor weather forecasts, especially during periods of high intensity rainfall. Remaining vigilant and proactive in response to changing weather conditions enhances overall preparedness and safety. 


During times of potential threat, it is crucial to heed the guidance of local authorities. Californians should stay informed about official communications, evacuation orders and safety instructions issued by emergency services. Following the directives of authorities ensures a coordinated and effective community response and could save your life.  


Severe weather conditions can create power outages. Sign up for local alerts with your utility company to stay informed about possible power outages and public safety power shutoffs in your area. For those that are at high risk and require power for medical needs contact your local utility providers for the medical baseline program which offers early notifications of possible shutoffs giving Californians time to adjust their emergency plans. Generators can also be helpful when the power goes out. Generators should be used properly, like using them outdoors and keeping them dry and protected from the elements. 


After assessing your local risks, review your insurance coverage. Ensure that you have the correct coverage for your property’s risk. Standard homeowner’s insurance may not always include floods, fires, mudslides, or earthquakes.