Extreme weather, climate change, and the Oso WA landslide

Over the weekend a big landslide struck Oso, WA, located on the Stillaguamish River about an hour north of Seattle. It’s a tragedy of large order, with several already confirmed dead, reports from emergency workers saying it’s worse than has yet been reported, whole neighborhoods wiped out, etc. I’ll pop in a few links down at the bottom of news reports going over these details. Instead what I want to do is focus on the big picture – to what extent was this caused by climate change, what’s the economic impact of events like this, and will events like this increase or decrease in the coming years.

Bottom line is that the Seattle Area (Oso is just north of Seattle) has had heavy rainfall this winter. The heavy rainfall caused the Oso landslide, because that vicinity was prone to landslides. In fact that very hillside had had a landslide eight years ago. And the Washington Dept of Transportation had just finished a landslide mitigation project just across the river.

The rain we did not get in California instead fell in the Northwest, thanks to a semi-permanent high pressure system in the Pacific Ocean which redirected the normal winter rains northward. As a result California is having a severe drought, while the Pacific Northwest is receiving higher than usual rainfall.

Sea-Tac airport recorded 7.22 inches of rain between March 1 and March 16, 2014, or 3 times what is normally seen. While researching this I saw plenty of news reports from the Winter of 2014 about wetter-than-usual weather. In December 2013, KOMO News wrote a piece about 2013’s weather, saying the two wettest months of 2013 were in months (September and April) that are typically dry months (for Seattle). Both of the months recorded rainfall 2-3 times the average for those months.

I wrote more details about the wetter than usual weather in the Seattle Area in a report on examiner.com

. What’s going on is changing weather patterns.

Typically, the winter months cause a lot of rain storms along the West Coast, but the usual pattern is for California to receive a lot of rain. That rain is captured in reservoirs all through California, and we drink it all summer long (when it typically doesn’t rain at all). But the last few winters have been extremely dry in California, and Gov. Brown just declared a Water Emergency because the entire state is in either moderate or heavy drought conditions.

That’s part of the changed weather pattern – California is dryer than normal. Because the new weather pattern is directing the winter storms northward, the Northwest is wetter than usual.

Obviously waterlogged hillsides can fall down and that’s what happened in Oso last weekend. The Seattle Times carried a piece discussing the history of landslides in that river valley

. It would be easy to look at that historical information and dismiss climate change effects (“that’s not climate change – that’s terrain”). However, what would be more accurate is to say Oso was vulnerable to landslides, and that heavy rains consistent with climate change weather changes triggered the landslide.

Will climate change cause more of this sort of damage? Here I am turning to a press release from 2011 posted by the Union of Concerned Scientists

. That press release discusses the mechanism of rising temperatures that lead to heavy rainfall.

Carbon dioxide from burning fossil fuels and destroyed tropical forests accumulates in the atmosphere, trapping heat that would otherwise escape into space, This trapped heat raises the planet’s average temperature. Some of the extra heat evaporates water from the ocean and soil into the atmosphere. Additionally, growing plants transfer water vapor into the atmosphere.

As average global temperatures rise, the warmer atmosphere can also hold more moisture, about 4 percent more per degree Fahrenheit temperature increase. Thus, when storms occur there is more water vapor available in the atmosphere to fall as rain, snow or hail. Worldwide, water vapor over oceans has increased by about 4 percent since 1970 according to the 2007 U.N. Intergovernmental Panel on Climate Change report, its most recent.

It only takes a small change in the amount of water vapor in the atmosphere to have a major effect. That’s because storms can draw upon water vapor from regions 10 to 25 times larger than the specific area where the rain or snow actually falls.

According to the U.S. Global Change Research Program’s (USGCRP) most recent report, scientists have observed less rain falling in light precipitation events and more rain falling in the heaviest precipitation events across the United States. From 1958 to 2007, the amount of rainfall in the heaviest 1 percent of storms increased 31 percent, on average, in the Midwest and 20 percent in the Southeast.

After a heavy precipitation event, there is less water vapor in the atmosphere, and therefore dry spells tend to be longer. In the absence of rain, extra heat exacerbates drying and can contribute to longer and more intense drought periods.

USGCRP has projected that climate change is likely to increase the disparity between light and heavy precipitation events.

That was a lot of words, but they sum up to this: When it rains, it pours.

That is, more water in the atmosphere (because of higher evaporation rates) means heavier rainfall, in places where rain falls.

Heavier rainfall is an example of the sort of increase in extreme weather that’s expected from climate change. Though, the impact of climate change is going to vary from place to place – as we saw, it’s giving California a drought while the Northwest is being inundated with rain.

It therefore seems very likely that as the temperature rises, we’ll be seeing more and more heavy rain (in some places) because the atmosphere will be holding more water.UPDATE: ThinkProgress

posted a very interesting writeup focusing on the same line of reasoning as is shown here.

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About David Herron

David Herron is a writer and software engineer living in Silicon Valley. He primarily writes about electric vehicles, clean energy systems, climate change, peak oil and related issues. When not writing he indulges in software projects and is sometimes employed as a software engineer. David has written for sites like PlugInCars and TorqueNews, and worked for companies like Sun Microsystems and Yahoo.