Flooding Could Double in High Rugged Regions

Washington state’s Cascade Mountains hold some of the Pacific Northwest’s most rugged terrain — a well-known fact to hikers, bikers, hunters and anglers who have explored these treasured areas. Understanding how climate change may affect the roads and trails needed to access these lands for recreation and management is the focus of a recent paper in Climatic Change.

To understand how climate change will impact transportation in northern Washington’s public lands including the North Cascades and Mount Rainier national parks, land managers and research scientists formed the North Cascadia Adaptation Partnership in 2010. The collaboration covers an area roughly the size of Vermont with enough roads and trails to equal a road trip from Seattle to the southern tip of South America and back again.

The team first assessed vulnerabilities based on projections from two global climate models that represent high and low-level climate change along with hydrological simulations. The researchers looked at how the climate scenarios would influence 100-year flooding events and soil moisture saturation (a rough indicator of landslide activity) when 90 percent of the snowpack had melted. The goal was to estimate when visitors would be able to access high-elevation areas.

Some basins could experience a doubling of 100-year flood frequency as soon as the 2040s, the assessment suggested. The portion of roads in mixed rain-snow basins — those that received their precipitation as a mix of rain and snow and where flooding hazards are often most pronounced —could increase from 37 percent in the Okanogan-Wenatchee National Forest today to nearly 100 percent by the 2080s.

This collaboration, in contrast to some vulnerability assessments, relied on managers’ experience and understanding of the landscape. Perhaps more importantly, it identified management responses to maintaining access. The first set of responses focused on “no-regrets” strategies — basically, activities that are high priorities, regardless of climate change. For example, many bridges and culverts already need upgrading to resist high flows or improve fish passage. Similarly, improving drainage, stabilizing slopes and restoring vegetation reduces landslide risks, particularly in places vulnerable to climate change. In the longer term, the researchers found, more extensive effort may be required, such as decommissioning or rerouting roads and trails most prone to flooding and landslides.

While this paper focuses on transportation, the collaboration looked at a much broader set of resources, including vegetation, wildlife and fish. Since 2010, this effort has been repeated in several other regions, including a project to which CIRC contributed in the Blue Mountains in northeastern Oregon and the Northern Rockies in Montana and Idaho. You can learn more about these efforts on our website.

Citation: Strauch, R.L., C. L. Raymond, R. M. Rochefort, A. F. Hamlet and C. Lauver (2015), Adapting transportation to climate change on federal lands in Washington State, U.S.A., Climatic Change, 130, 2, 185–199, doi 10.1007/s10584-015-1357-7.You can learn about this effort on the North Cascadia Adaptation Partnership’s website.

Photo Caption: Undermined Nisqually Road, Mount Rainier National Park (Photo Credit, National Park Service, this image is in the public domain.)

John Stevenson is CIRC’s Regional Extension Climate Specialist, a position jointly-funded by CIRC and Oregon Sea Grant. Follow him on Twitter @CIRC_Extension.