Post-wildfire mudslides and floods were previously linked to the buildup of waxy coating over burnt soil, which prevents the ground from absorbing water. However, researchers have discovered that the flow of water originates from absorbed underground water in both unburnt and burnt regions. This suggests the surprising role that underground water accumulation plays in post-wildfire floods and mudslides.
Devastating Wildfires
Back in 2020, a mega wildfire, known as the Bobcat Fire, blazed through Los Angeles County and burnt over 115,000 acres. Over 150 structures were also damaged or destroyed, while smoke and ash rained down over residents of Los Angeles.
Science Daily explains that after the wild flames were tamed, the fire had immense potential to cause worse damage. As rainstorms surge over charred areas, mudslides, floods, and debris flow can accelerate the damage of the wildfire.
Knowing more about the accumulation of water and being able to monitor its runoff and flow in charred areas could help authorities know more about the occurrence of such post-wildfire events. With this, residents could be granted early warnings of debris flows or flash floods.
Read also: Wildfires Causes: Human-Induced Climate Change Blamed for Increasing Uncontrolled Fires Worldwide
Post-Wildfire Mudslides and Floods
Mirage News reports that it is common knowledge that vegetation loss during fire makes soil vulnerable to erosion due to the withering or death of plant roots. However, scientists have thought differently, holding that with burning leaves, the waxy coating turns into an oily and organic substance that covers the surface of the soil and produces a layer over the surface that repels water. They believed that such layers hampered the ground's absorption of water, which could have led to the fast runoff of water.
Now, a new study questions this theory. Scientists from the USC Dornsife College of Letters, Arts, and Science partnered with researchers from the US Geological Survey, the University of Michigan, and Rutgers University to know more about this. From December 2020 up to March 2022, they looked into two wet seasons that took place after the Bobcat Fire.
They specifically looked into three watersheds, which are land areas that drain snowmelt and rainfall into rivers and streams. These watersheds were in the San Gabriel Mountains in Southern Carolina. Two of these burned during the Bobcat Fire, while the other remained virtually untouched.
The researchers discovered that after the wildfire, a huge portion of the flow of water in the three watersheds, was from underground water that was absorbed. Hence, they concluded that burnt ground, which contained the waxy coating of leaves, actually absorbed water.
Earth sciences professor Joshua West, who directed the study at USC Dornsife, explains that what was surprising was that stormwater entered the ground in both watersheds that were burnt. As such, these findings go against previous notions that minimal water gets absorbed in burn watersheds due to waxy coatings.
For the unburnt watershed, the researchers observed that water was absorbed by trees, as expected. This, in turn, stopped the water from arriving at the streams.
The findings support their hypothesis that streams of water come from groundwater and rainfall, which leads to heightened flooding in burnt areas compared to unburnt ones.
Professor West explains that the abundance of water levels in areas where the Bobcat Fire burned could help with future concerns pertaining to flooding. He is sure that the findings carry vital information that the USGS could make use of to boost monitoring of burnt areas and predictions of post-wildfire mudslides and floods.
RELATED ARTICLE : The Serious Effects of Wildfires on Water and the Environment
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