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Updated 12 October, 2003

US National Assessment of
the Potential Consequences
of Climate Variability and Change
Educational Resources
Regional Paper: Pacific Northwest


 

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Coasts

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The Pacific Northwest's rich coastal ecosystems include: estuaries (where freshwater meets salt water), inland marine waters (e.g., Puget Sound), and the open coasts along the Pacific Ocean. Small cities and towns, dairy and farmlands still characterize the shorelines of the low-lying coastal estuaries of Oregon and southern Washington. These areas support extensive shellfish harvesting on their mudflats and in their shallow waters. The Puget Sound coast and the Strait of Juan de Fuca contain intense development and expensive homes, on bluffs and beaches, as well as suburban communities and the remains of once dominant forest and agricultural industries. These inland marine waters are bordered by narrow beaches backed by steep bluffs.

The open Pacific Coast is characterized by steep rocky bluffs and headlands, with occasional small pocket beaches and sandspits, in southern Washington and coastal sand dunes in central Oregon. The area is lightly developed (with some portions becoming increasingly developed) and significant portions of its land are in the hands of the public (e.g., parks) and within the boundaries of Indian reservations.

Extensive development on coastal bluffs and near beaches, mainly in Puget Sound but increasingly also along the Pacific coast, has placed considerable valuable property at risk from erosion and landslides. The low coastlines near major river-mouths are sensitive to flooding, to ocean erosion from storm waves, and to variation in the amount and type of sediment carried by the rivers, which has increased on some rivers as a result of adjacent clear-cutting, and decreased on others (including the Columbia) as a result of damming. Other stresses in coastal regions presently include loss of wetlands to development or erosion and invasion by exotic (non-native) species, particularly in the coastal estuaries.

The long-term effects of climate change on the coastal zones of the Pacific Northwest are likely to be similar and even more serious than those climate impacts already felt in the region. Some of the environmental, social and economic impacts are discussed below. Strategies that could be used to address potential affects conclude this discussion.

Environmental Impacts

Only limited amounts of long-term data are available on coastal effects of climate variability, but a few effects are evident. Severe storm surges (larger than normal waves and swells) and erosion events on the open coast occur on average every five years. These appear to be associated with El Niño events, which increase erosion, both by raising sea level for several months and by changing the direction of winds and waves from westerly to southwesterly. The 1997-1998 El Niño, for example, brought rapid erosion to a 1,000-foot built up segment of the sandspit on which Ocean Shores, Washington is situated. This erosion reversed several centuries of slow growth and required emergency construction of an armored beach fill.

One Oregon study found that construction of shore protection measures follows an ENSO cycle, increasing sharply in the years immediately following a strong El Niño. As well as causing extreme erosion events, the elevated sea level during El Niño events also increases inundation risk in the low-lying areas of southern Puget Sound such as the city of Olympia. In contrast, La Niña events bring reduced erosion on the open coastline, but the heavier than normal winter rainfalls increase soil saturation and landsliding risk on coastal bluffs. For example, the four years with highest landslide incidence in the Seattle area were all La Niña winters (1933-4, 1985-6, 1996-7, 1998-9).

There is also some suggestion of PDO effects in the coastal region, although this is still speculative. For example, the warm decade of the 1980s that followed the shift to warm-phase PDO in the late 1970s, was marked by two striking shifts in the ecosystem of Willapa Bay in southern Washington. The exotic cordgrass (Spartina), which was introduced to the bay nearly 100 years earlier, began a rapid expansion that threatened local species for the first time. After several productive decades, the condition of commercially important oysters in Willapa Bay also began a substantial decline in the late 1970s, though other factors such as pollution in the Bay could also be responsible for their decline.

Several coastal effects of future climate change have been identified, although detailed assessment of these remains to be done. Future climate warming is likely to raise mean global sea level 4 to 35 inches in the 21st century, as opposed to the 4 to 8 inch rise of the 20th century. Although absolute sea level is rising in all oceans, trends of sea level compared to changes in land levels vary greatly from place to place. The variation is partly due to regional differences in ocean circulation and heat content -- for example, one of the models projects a larger sea-level rise on the Pacific than the Atlantic coast of North America.

It is also partly due to local variation in the rate of uplift or subsidence (sinking) of the land surface itself. In the Pacific Northwest, there are basically 2 regions of uplifting land, one centered at the mouth of the Strait of Juan de Fuca, rising at 0.1 inch per year, and the other at the mouth of the Columbia River, rising by 0.06 inch per year. The southern portion of Puget Sound, on the other hand, is sinking at up to 0.08 inch per year. As a result of this subsidence, risks of sea-level rise are greatest in southern Puget Sound. Here, low-lying settlements are already at risk from projected average sea-level rise and are at even greater risk from average sea-level rise combined with storm waves.

Higher average sea level is also likely to increase erosion and sediment redistribution along the open coast. Erosion here could possibly be further increased by projected changes in prevailing wind direction that would resemble sustained El Niño conditions. In addition, projected heavier winter rainfall is likely to increase soil saturation, landsliding, and winter flooding. All these changes would increase the risk to property and infrastructure on bluffs, beachfronts, and beside rivers. Climate change could also bring continued changes in coastal and estuarine ecosystems through changes in runoff and warmer water temperatures, with possible increased risk of exotic (non-native) species introduction or health risks from shellfish contamination.

Social and Economic Impacts

The aesthetic and recreational value afforded by some coastal areas could be impacted by sea-level rise and by a potentially increased frequency or change in direction of severe storms. However, any future changes in storm frequency and direction, are still quite speculative. In fact, the warmer summers could support both positive (e.g., longer tourist seasons) and negative (e.g., fresh water stresses) aspects of seasonal visits to the communities along the Pacific Coast. As air and sea surface temperatures generally rise, the preferred location for commercial fisheries could shift, providing the possibility for new opportunities, as well as difficulties, to sustain a source of livelihood that has been a way of life in some coastal communities for many generations. Recreational fishing is enjoyed by many residents and visitors, however, it could change in certain locations if climate changes as projected. The service industries that support such tourism and outdoor recreation -- hotels, inns, restaurants, and travel services could also be affected both positively and negatively by any changes in the region's climate.

Challenges posed by regional climate changes will be felt by both private and public entities. In some locations, concerns turn to expensive properties that have been built directly along the shoreline, in low-lying areas, or on the top of unstable bluffs. These properties have the potential to be flooded, suffer storm damage, or threatened by erosion and landslides. Loss of infrastructure (stormwater or sewage treatment plants or roads, for example) located in threatened areas could cost a community a significant effort and financial loss if they needed to be protected or replaced.

An important aspect of social and economic impacts to coastal areas from climate changes relates to how coastal managers use climate information. A survey of coastal managers suggests that the coastal management system is not particularly adaptable even to current climate variability and its associated risks. For example, there appears to be little inclination to move in the direction of restricting development in vulnerable locations to avoid future problems. Many coastal managers report that they do not view the long-range threat of flooding or inundation as a significant risk to the resources they manage. Most managers reported that they are seriously constrained in their ability to incorporate climate in planning, indeed that any climate considerations are overwhelmed in their planning by the present and potential endangered listings of various salmon species.

Strategies to Address Potential Impacts on Coastal Areas

Strategies that could be useful in avoiding or mitigating climate-change impacts on the built and natural resources in coastal areas vary in their approach. At least three strategies are available to cope with the effects of climate change on the built infrastructure along the Pacific Northwest coastal areas and the retreat option assists the natural areas as well. The options include:

  • conserve remaining natural coastal areas and place less property at risk in low-lying or flood-prone areas, on beaches, or on and below unstable slopes -- in other words retreat from advancing seas and unstable areas;
  • accommodate changes imposed by a higher sea level or threat of flooding; or
  • protect areas/structures from sea-level rise, flooding, and inundation.
    • All of the above coping strategies could be more effectively applied through education efforts that help concerned parties cope with potential coastal changes. For example, all stakeholders should be informed about the risks of building in hazard-prone areas and likely changes in storm frequency, intensity, and sea level.
    • Assigning more of the risk of living in a coastal zone to property owners, could be accomplished through incorporating geological assessment into property-insurance rates.

    Specific actions that could be undertaken to facilitate coping with coastal zone changes could include the following.

    A strategy of retreat is particularly appropriate if we want to allow for ecosystem migration. Retreat could include the following actions:

    • establish setbacks in building codes that require structures vulnerable to inundation be moved if threatened (similar codes are in place in other states);
    • buy coastal land and prohibit its development;
    • include present and projected sea-level rise in planning and development, along with anticipatory building codes; and
    • remove subsidized coastal flood insurance.

    Accommodation could entail the following steps:

    • regulate building development by instituting stronger and more appropriate building codes and restricted locations; and
    • develop and offer incentives to encourage responsible decisions.

    A strategy designed to protect coastal lands along economically valuable shorelines could include efforts to:

    • nourish protective beaches; and
    • construct bulkheads and sea walls.

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