The Pacific Northwest will only get wetter with climate change, researchers say

Story by Cassidy Thornton

Rain, rain, here to stay — says the future forecast of the Pacific Northwest. Scientists predict climate change will make the region’s rain more extreme.

A new 2017 study provides a glimpse into this future, examining changes in land use and climate on landslides in the Pacific Northwest. This study comes just five years after a devastating landslide killed 43 people near Darrington, Washington.

Washington State University researchers warn that logged forests are more susceptible to landslides as the Pacific Northwest climate changes. The research was the first of its kind to examine the link between landslides and climate change in the Pacific Northwest.

According to their findings, landslides are becoming increasingly frequent due to land use and climate changes.

Rain plays a key role in controlling landslide activity, a 2008 study from Environmental Geology found, and due to this, landslides will likely become a common occurrence in the rainy Pacific Northwest.

The Pacific Northwest is expected to receive wetter winters under climate change, resulting in saturated, unstable soils that are more susceptible to landslides, said Jennifer Adam, the study’s co-author and associate professor in Civil and Engineering at Washington State University.

This, combined with the loss of tree’s root structures in clear-cut areas, further reduces soil stability, she added.

The core of this research focuses on human needs and environmental protections. “We try to identify win-win situations,” said Adam.

The study identifies features of vulnerable areas to help forest managers continue sustainable timber extraction under the increased risk of landslides.

To do this, researchers digitally recreated the Queets watershed in the Olympic Peninsula. The strikingly green temperate forests, steep terrain and pockets of timber production in this region were transformed into numerical values to plug into models.

They used a hydrologic model to determine the likelihood of water-induced landslides. This model took into account variations in land use, soil, landscape features and subsurface moisture.

Researchers were most concerned about wet soil conditions combined with a loss of vegetation. Characteristics prominent in the Olympic Peninsula, which receives two to six meters of rain each year on timber-harvested lands, according to the National Oceanic and Atmospheric Administration.

Most landslide studies are based on historical data, but this research also looks at future projections. Researchers used two greenhouse gas emission scenarios to represent the highest and lowest emission scenarios for 2045.

The final results were nine years in the making, said Muhammad Barik, the study’s co-author and associate scientist at Universities Space Research Association, a nonprofit research organization.

Barik explained that after compiling the results, the research team immediately began to write their publication. They were eager to publish their study as a tool, and a warning for climate change impacts.

Their study showed a seven to 11 percent increase in land highly vulnerable to landslides across the Olympic Peninsula. This means areas considered suitable for logging today could become vulnerable to landslides in the future, Adam said.

From these results, researchers created landslide susceptibility maps that pave the way for new, more informed forest management plans. The hope is that these plans will help minimize the effects of future logging-induced landslides, Adam said.

Their findings can be further used by managers of temperate rainforests and mountainous regions worldwide to better assess landslide potential.

According to Adam, this study and its result did have shortcomings.

In an ideal situation, researchers would run the model all over Washington State, but that requires significant computing resources, Adam said.

“Research around soil stability is a really fine-scale process, it requires a high level of detail and resources,” Adam said, explaining the difficulties of the study.

David Montgomery, a professor at University of Washington who was not involved in the study, said the research implemented the best-available science for exploring “what if” scenarios.

The study is already successfully opening dialogues about this issue.

After its publication, Barik was approached by forest managers asking how they can apply this new finding. “And that was the ultimate goal of our results,” Barik said.