Despite their seemingly opposite nature, fires and floods are often linked to natural disasters. After all, since flames dry out plants and destroy excess plant matter, they would reduce the likelihood of flooding. But the connection between floods and fires is more nuanced than it first appears.
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- What is the reason why floods usually follow fires?
- What happens when debris flows?
- How does a debris flow work?
- Why do debris flows present such a risk?
- Connection with drought
What is the reason why floods usually follow fires?
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The NWS issues a warning because wildfires can permanently alter the environment and increase the danger of flooding for many years. In and around steep terrain, locations downstream and downhill from burned areas are most vulnerable to debris flows and flash flooding.
When the fire burns hot enough or long enough, the soils in those regions form a layer that, when it rains, actually deters water, much like rain on pavement.
Precipitation that would often be absorbed by vegetative debris in the soil and forest cover will run off quickly. Because of this, substantially less precipitation is needed to cause a flash flood, and the potential for debris flows increases due to the destruction of plant life that stabilizes the soil.
What happens when debris flows?
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The most frequent time for debris flows after wildfires is during heavy rain. A steep slope or a prolonged downpour is not necessary for debris flow. On a dry slope, it may start after a few minutes of heavy rain.
“Heavy” rain is a sudden downpour that lasts about half an hour. Precipitation rate is more important than total precipitation when it comes to debris flows.
How does a debris flow work?
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Debris flows are deadly, fast-moving landslides. They are strong mixtures of dirt, pebbles, large rocks, whole trees, and occasionally houses or cars. “Debris flows” are sometimes called “mudslides” or “mudflows.”
Although many people use the terms synonymously, experts distinguish between the three types of landslides, with debris flows being the most powerful and dangerous.
Why do debris flows present such a risk?
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Debris flows occur quickly and without warning. They can catch up to your car faster than you can run! Additionally, people need to know where and when debris flows will begin.
It could start in a creek channel, then emerge and take over a residential area. Debris flows can develop in previously unexplored areas or in areas that have never occurred.
Connection with drought
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Droughts frequently fuel fires. Although recent moderate rains may have given the impression that the drought has disappeared, it is still officially declared severe. According to FEMA, it can take up to five years for the landscape to recover from a fire in a way that reduces the risk of flooding.
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Source: vtt.edu.vn