Almost all states have received 400% to 600% more rain than the average since Christmas. With some areas receiving up to 30 inches. Causing widespread flooding and landslides.
SAN DIEGO — Relentless storm surges from. A series of atmospheric rivers have saturated wildfire. Scarred steep cliffs and bald cliffs along much of California’s long coastline. Causing hundreds of landslides this month.
So far debris has blocked most roads and highways. And not damaged communities like in 2018. When mudslides in Montecito killed 23 people and wiped out 130 homes. But with more rain forecast, fears will increase.
Experts say California has learned important lessons from the Montecito tragedy. And has more equipment to identify hot spots and more basins and nets to capture falling debris. Before it hits homes. Recent storms are putting those efforts to the test. As climate change creates more severe weather.
Why is California prone to mudslides?
Geologically speaking, California has relatively young mountains. Meaning much of its steep terrain is still mobile and covered in loose rock and soil that can be easily eroded. Especially when the soil is wet, according to geologists.
Almost all states have seen 400% to 600% more rainfall. Than the average since Christmas, with some areas receiving up to 30 inches. causing widespread flooding. At least 19 people have died in the Severe weather since late December.
Since New Year’s Eve, the California Department of Conservation’s landslide. Mapping team has documented more than 300 landslides.
Prolonged drought in the state has worsened the situation.
Dan Sugar, an associate professor of geosciences at the University of Calgary. Said the drought could have the opposite effect. When combined with the incredible rainfall in California in recent days. “You’d think if the soil was dry it would be able to absorb a lot of water, but when the soil gets too dry. The permeability of the soil actually decreases,” he said. As the water moves away from the hardened soil, moves downstream and gathers energy. It begins to carry soil and debris away, he said.
Added to this, the wildfires left little vegetation to hold the soil on some hillsides.
What are the most vulnerable areas?
Jeremy Lancaster, who leads the California Department. Of Conservation’s geologist and landslide mapping team. Said the most vulnerable areas are hillsides that have burned. In the past two to three years with the communities below them.
That includes areas recently burned in Napa, Mariposa and Monterey counties, he said.
In 2018, the fatal mudslide in Montecito occurred about. A month after the largest wildfire in California history. burning 280,000 acres in the same area.
On the fifth anniversary of that tragedy. The entire community was ordered to evacuate. On January 9 as rain lashed the area and debris blocked roads.
Lancaster warned that even after the rain subsides. The threat of landslides will linger. As water seeps 50 to 100 feet into the ground and destroys things. What can be done to protect the community?
California has dramatically stepped up efforts to identify hotspots since the Montecito mudslide. Lancaster said. His department constantly updates its maps so local communities are aware. And can make decisions, including whether to evacuate an entire community. The state is also working on a system to better identify how much rain can trigger landslides.
Maarten Geertsema, who studies natural hazards and terrain analysis. At the University of Northern British Columbia. Said agencies use a variety of tools to gauge. The likelihood of landslides in a given area, including terrain maps and lidar. Pulsed light from lasers that penetrates tree foliage. See the ground They can then look for early warnings. Such as in photos taken from the air over time, or from satellites. Or in data from GPS monitoring stations. Tilt meters and or other on-site instrumentation.
What is the most effective defense against mudslides?
But basins, which can must a lot of land, can also disrupt natural ecosystems and. According to experts, beaches must be replenished by collecting sediment runoff from canyons.
And they’re expensive, says Douglas Gerolmack, a professor of environmental science. And mechanical engineering at the University of Pennsylvania.