A fatal landslide on Saturday morning tore down a small community in northwest Washington state, killing at least eight people. Officials said the cause of the landslide was ground saturation resulting from recent heavy rainfall. This March was the sixth-wettest since 1922, according to Johnny Burg, a National Weather Service meteorologist in Seattle who spoke with the New York Times, who also said the rains followed a drier-than-normal spell from October to January.
“That kind of heavy rain really saturates the ground to the point where it cannot hold any more water,” Burg told the New York Times. “And that creates instability, especially on steep hillsides.”
The mudslide measured about a square-mile and obliterated nearly 50 structures, 25 of which were single-family residences, in Arlington, a small town nestled between a river and the hills about an hour northwest of Seattle. As of Monday morning, John Pennington, Snohomish County emergency management director said that there had been 108 reports of missing people, which is different than 108 missing people. The number includes construction workers who came to the area and also people driving by, though more people were likely to be home on a Saturday morning.
Landslides are not unusual in Washington, but such a large one in close proximity to residences is more rare. Landslides cost the nation several billion dollars in damages annually according to the United States Geological Survey, and cause 25 to 50 deaths per year. The Pacific Northwest is predicted to get warmer and wetter according to climate change models, which will likely add to the economic and human costs associated with landslides in the region.
The average annual precipitation in Washington has increased by about one-third of an inch each decade since the beginning of the 20th century. Temperature averages have also increased about 1.5°F since 1920, with climate models projecting increases in annual temperature of, on average, 2.0°F by the 2020s, 3.2 °F by the 2040s, and 5.3°F by the 2080s.
“More extreme rain events –- the sudden and intense rain that we’ve been experiencing more frequently so a lot of the state routes are vulnerable to landslides today and the projections are that those will be worse,” Carol Lee Roalkvam, an environmental policy analyst with the Washington State Department of Transportation, told Oregon Public Broadcasting last year.
According to the University of Washington Climate Impacts Group, in the near future climate change will cause the region to see less snowpack, earlier snowmelt, and more winter rainfall, leading to more landslides.
“If the climate changes in a way that we get a lot more rainfall you would expect to see a lot more landslides,” Dave Montgomery, a geologist at the University of Washington, told EarthFix this week. “The character of the rainfall that we get, whether it’s more high intensity rain or more of the long soak would actually influence the type and style of landslides that we might expect to get but the short answer is, you know, if we get more rainfall we ought to expect to see more landslides and this region already is landslide-prone.”
Montgomery is concerned about public education and awareness when it comes to societal impacts of climate change. He notes that it appeared that a landslide had occurred in the region before, and wonders if the people living there knew the risk. The same informational component is important when it comes to raising awareness of the risks of living near the coast as the sea level rises; or living in heavily forested areas in the West as wildfire season grows longer and more severe; or living in already arid and overpopulated regions, like Phoenix or Las Vegas, as climate change causes them to get hotter and drier.
Flood zones are another area of risk as the U.K. has seen several months of record-setting rainfall lead to flooding disasters across the region, viewed as a forewarning of climate change’s impacts to come. A recent study found that extreme floods in Europe will become significantly more common by mid-century.
Snohomish County, the area hit by the landslide, remains under a flash flood watch at least until Monday afternoon. While flash flooding is already a concern for Washington during periods of heavy rainfall, the landslide has complicated the matter by blocking a river and creating the potential for a catastrophic flood. However the latest reports indicate that water has found a way through the debris, decreasing the risk of major flooding on top of the landslide.