Wildfires that destroy vegetation and char the ground also reduce the ability of soil to absorb water when it rains. In the Western United States it’s common for wildfires to occur in the fall dry season and be followed by winter rains. This means that properties in the impacted region become vulnerable to flooding, erosion, mudflow and debris flow damage resulting from post-wildfire rains. 
Your agent or insurer will tell you that standard home insurance policies exclude coverage for damage due to flooding, mudslides, mudflow, landslides and debris flow. But if you have proof that your property was damaged by a flood or mudflow that was triggered or “proximately caused” by an event that is covered, (fire, accidental breakage) you should provide that proof to your insurer and follow United Policyholders’ guidance on making your strongest case to get them to reverse their claim denial.
Property owners in wildfire-impacted communities have an increased risk of damage from debris, slides and mudflow, home and business owners should take preventative steps and be aware of limitations and exclusions in standard policies for those categories of damage. Using sandbags, wattles and other flood and erosion control strategies is critically important to protecting life and property in regions that have been impacted by wildfires. Check with your local government on any program or help they may offer. Insurers rarely will pay for work that’s necessary to prevent imminent damage. You should do all you can to protect your property and household.
You can (and should) buy flood insurance if you can afford it. Note: Most flood policies have a 30-day waiting period after purchase during which no claims will be covered. This is designed to prevent people from buying insurance for a loss already in progress. 
If you find yourself in a situation where a relatively recent wildfire burned hillsides and areas near your home and caused mud or debris flow that damaged your property, you can make a claim under your home policy, (even if you have no coverage for flood damage) on the grounds that the fire (a covered peril) caused the flow that caused the damage.
Professional water, soil and weather experts have long recognized that there is a “fire-flood” sequence that occurs after wildfires. If it can be shown that a wildfire (a peril covered by your homeowners policy) was the most important (in legalese “efficient proximate”) cause of damage, you have a strong argument that your insurer should cover repairs. Your success will depend on how recent and close the fire was to the origination of the mud/debris flow.
Following a tragic mudslide and debris flow that destroyed lives and homes in the town of Montecito in 2018, the California legislature clarified that if a loss results from a combination of perils, one of which is a landslide, mudslide, mudflow, or debris flow, coverage shall be provided under the same terms and conditions as they would for covered peril (fire). (Cal Ins Code § 530.5).
The California Department of Insurance issued notices in 2018 and 2021 alerting insurers that exclusions for mudflow, debris flow, mudslide, landslide, or other similar events will be unenforceable if facts establish that a covered peril (fire) was the “proximate cause” of those events.
View the 2018 CDI Alert
View the 2021 CDI Alert
If a wildfire is not determined to be the “proximate cause” of damage to your home and you have a Flood Policy issued by the National Flood Insurance Program or another flood insurance provider, you should have coverage for the damage, especially if there was extensive liquid/mud with the debris. Read “The dirt” on insurance protection for mud flow damage for more information.
 Damage-causing events are referred to as “perils.” Fire is a peril. Flooding is a peril. Policy wording determines which perils are covered and which are not. Generally speaking, ambiguities in insurance policies give the consumer the right to have an ambiguous exclusion interpreted as it makes sense to them, as long as their interpretation is reasonable.
 For more info, see:
 Post-Fire Flooding and Debris Flow, https://www.usgs.gov/centers/ca-water/science/post-fire-flooding-and-debris-flow?qt-science_center_objects=0#qt-science_center_objects