Monday, April 7, 2014

Heavy Rains Link Climate Change and Landslides

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 hydrological research.

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 report stated.
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 U.S.

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 explains.
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 especially prone.

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 landslides.

As explained in the British Columbia study, “Glaciers and permafrost will continue to melt, and landslide regimes will ultimately respond to all of these drivers.”

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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