The recent deadly landslide in Washington state has led a number of publications to explore the possible influence of climate change. A landslide, defined as the downward movement of slope under the influence of gravity, can be triggered by a number of changes including weaknesses in composition or structure of the rock or soil and high precipitation. Rainfall, particularly heavy rainfall is the causal element that connects climate change to landslides and it is the focus of this article.
While the causal factors involved in landslides are complex, there is a
strong body of research which supports the idea that climate change will
increase the number of slides. The key factor connecting climate change to
landslides is water. This linkage has been evinced in both geological and
As University of Washington geologist Dave Montgomery explained in an interview with Earthfix, “if
the climate changes in a way that we get a lot more rainfall you would expect to
see a lot more landslides.” The relationship between increased heavy rainfalls
and climate change is widely documented. In 2007, the Intergovernmental Panel on
Climate Change (IPCC) Working Group l reported that we can expect more extreme
weather including heavy rains.
“More precipitation now falls as rain rather than snow in northern regions.
Widespread increases in heavy precipitation events have been observed,” the IPCC
These observations have been reiterated in subsequent IPCC reports including
the recently released AR5
Working Group ll. This report specifically pointed to “Increases in rainfall
and wet weather…” in North America.
Less than three years ago, the Union of Concerned Scientists reviewed how climate change contributes to heavy rainfalls.
On Saturday March 22, a rural Washington state neighborhood 55 miles
northeast of Seattle, was decimated by a landslide. A total of 50 buildings were
destroyed and 29 bodies have been recovered, 19 others are still missing, some
of whom may never be found. The mudslide on the outskirts of the town of Oso in
Washington’s North Cascade Mountains measured about a square-mile and is as much
as 70 feet deep in some places.
While it is difficult to attribute an individual landslide to climate change,
we can say with a high degree of confidence that climate change is creating the
right conditions for an increase in the number of slides we will see in the
According to a research paper titled, Effect of climate change on
landslide behavior, “It is expected that shallow slips and debris flows
will take place more frequently as a consequence of more extreme weather
events.” The report also says, “glacial retreat and the melting of permafrost
will cause more landslides, debris flows and rock falls to occur.”
The Pacific Northwest already gets a lot of rain and the levels of
precipitation appear to be on the increase. National Weather Service
meteorologist, Johnny Burg told the New York Times that this March was one of
the wettest on record in the area.
An article in the Examiner said the landslide in Washington state happened because of too much
precipitation. They pointed to the inordinate rainfall witnessed in the
months preceding the event. Going all the way back to the preceding year the
area was receiving unusual amounts of rain. The King 5 news said that Sea-Tac
airport had three times the levels of rain usually recorded from March 2013 to
March of the following year. Even the normally dry month of September was far
wetter than usual.
In an April 2013, EarthFix article Jonathan Godt, a scientist with the US
Geological Survey who has studied landslides in Western Washington said the
culprit in landslides is adding water to gravity.
“You’ve got a steep slope and gravity wants to pull everything down and when
water enters the soil it changes the stress of the soil,” Godt
Carol Lee Roalkvam, the lead on environmental policy with the Washington
State Department of Transport, who co-authored an assessment of climate change
vulnerability, also subscribes to the view that we will see more landslides
attributable to rainfall.
“We’re aware now of more upriver flooding than we’ve seen in the past,” she
says. “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.”
In an NBC News article Ermel Quevedo, principal engineer and former
CEO of Landslide Technology explained it this way, “water puts so much pressure
that the dirt starts slipping.”
As reported in a Think Progress article, more rainfall and warmer temperatures
in the Pacific Northwest are expected to increase the number of landslides. The
average annual precipitation in Washington has increased by about one third of
an inch every ten years since the beginning of the 20th century. More intense
rainfalls will further increase the likelihood of a landslide. Temperature
increases in the Pacific Northwest may also play a role in increasing the
likelihood of landslides. The University of Washington Climate Impacts Group has
predicted that we will see earlier snowmelt and more precipitation in the form
of rain rather than snow.
There may already be evidence for the beginning of a trend in the Pacific
Northwest. As reviewed in the Earthfix article, in 2013, the corridor in
Washington State running along the shores of Puget Sound between Seattle and
Everett had one of its worse years ever for slides.
In March 2013, a massive landslide pushed 200,000 cubic yards of earth down
the west side of Whidbey Island.
Another landslide occurred this March on the south shore of Shuswap Lake,
north of Salmon Arm, B.C. The 150-feet long landslide took out power lines and
blocked a road.
A chapter of a research report titled Climate Change Effects on Watershed
Processes in British Columbia, makes the point convincingly, saying, “A
changing climate…is expected to have many important effects on watershed
processes that in turn will affect values such as…slope stability.” It went on
to predict, “an increased probability of droughts, floods, and landslides.”
The Pacific Northwest is hardly the only area in the US prone to landslides.
In the San Francisco Bay area, storms have caused large numbers of slides in
recent years. While landslides can occur in all 50 states, regions like the
Appalachian Mountains, the Rocky Mountains and the Pacific Coastal Ranges have
“severe landslide problems,” according to the United States Geological Survey
(USGS). The agency lists California, Oregon, Washington, Alaska and Hawaii as
While we cannot say for sure if inordinate rainfall caused the ground
saturation which led to the landslide in Washington state. We do know with a
high degree of certainty that climate change models predict more heavy rains,
more glacial melthing and more precipitation falling as rain rather than snow.
The research indicates that this will very likely increase the frequency of
As explained in the British Columbia study, “Glaciers and permafrost will
continue to melt, and landslide regimes will ultimately respond to all of these
Landmass movements can be added to the long and growing lists of costs
associated with climate change. The USGS says that landslides already cause
several billion dollars in damages annually, and kill between 25 to 50 people
each year. Going forward, we can expect to see more landslides due to climate
change and this will increase the damage and the death toll.
Source: Global Warming is Real
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