Flood After Fire
Flood After Fire Overview prepared by: https://www.fema.gov/fact-sheet/flood-risks-increase-after-fires
Floods are the most frequent and costly natural hazard in the nation. While some floods develop over time, flash floods particularly normal after wildfires can occur within minutes after the onset of a rainstorm. Even areas that are not traditionally flood-prone are at risk, due to changes to the landscape caused by fire. Residents need to protect their homes and assets with flood insurance now before a weather event occurs and it's too late. People are at greater risk of flooding due to recent wildfires that burned in their area. Flood risk remains a significant risk for ten years (or more) after a wildfire in the contributing watershed.
Understand flood-after-fire risk and approaches to risk mitigation in your community by sharing Flood after the Fire messaging from FEMA and the National Flood Insurance Program. The most important messages are:
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Buy Flood Insurance today. Only Flood Insurance Covers Flood Damage. Most standard homeowner's policies do not cover flood damage. Flood insurance is affordable, especially for homes in moderate- to low-risk areas
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The Time to Prepare is now. Gather supplies in case of a storm, strengthen your home against damage, and review your insurance coverages. It typically takes 30 days for a new flood insurance policy to go into effect, so get your policy now.
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Plan Ahead. Plan evacuation routes. Keep important papers in a safe, waterproof place. Conduct a home inventory, itemize and take pictures of possessions.
Flood After Fire: did you know wildfires dramatically alter the terrain and increase the risk of floods? Excessive amounts of rainfall can happen throughout the year. And properties directly affected by fires and those located below or downstream of burn areas are most at risk for flooding.
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During normal conditions, vegetation helps absorb rainwater but after an intense wildfire, burned vegetation and charred soil form a water repellent layer, blocking water absorption. During the next rainfall, water bounces off of the soil.
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Degree of Land Slope: Steeper slopes speed up water flow and increase flood risk.
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As a result, properties located below or downstream of the burn areas are at an increased risk for flooding.
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Flash Floods: intense rainfall can flood low-lying areas in less than six hours. Flash floods roll boulders, tear out trees and destroy buildings and bridges.
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Mudflows: rivers of liquid and flowing mud are caused by a combination of brush loss and subsequent heavy rains. Rapid snowmelt can also trigger mudflows.
The time to buy flood insurance is before the flood damage occurs. Typically, flood insurance policies have a 30-day hold time before they become effective. Contact your local insurance agent for more information or visit the National Flood Insurance Program at https://www.floodsmart.gov/wildfires.
What is a debris flow?
Debris flows are fast-moving, deadly landslides. They are powerful mixtures of mud, rocks, boulders, entire trees - and sometimes, homes or vehicles. You'll often hear "debris flows" called "mudslides" or "mudflows". Many people use the terms interchangeably, but to scientists, each is a different kind of landslide and debris flows are the most powerful and dangerous of the three.
What causes a debris flow?
Debris flows occur commonly during intense rain after wildfires. A debris flow doesn't need a long rain or a saturated slope. It can start on a dry slope after only a few minutes of intense rain.
"Intense” rain means a burst of rain at a fast rate, about half an inch in an hour. With debris flows, the rainfall rate matters more than total rainfall.
Why are debris flows so dangerous?
Debris flows are fast and unpredictable. They can travel faster than you can run - and they can catch up to your car! Also, no one can say precisely where a debris flow will start or where it will go. It may begin in a stream channel, then jump out and spread through a neighborhood. A debris flow may happen where others have occurred, or in a place that has never seen one before.
Flood after the Fire Resources Communication Resources: