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Coastal Hazards

Coastal Climate Change Effects

When faced with the question of how climate change will affect Oregon wetlands, the current answer seems to be "it depends". With the wide variety of ecoregions and wetland types in Oregon, climate change will probably affect wetlands in these ecoregions differently. Presently, much of the effort to assess the impacts of climate change has focused on the Oregon Coast due to the anticipated impacts of sea level rise, and increased storm intensities as the ocean warms. As our analyses and understanding increases, discussions of the effects of climate change in additional ecoregions will be added. The following discussion of the likely effects of climate change on the Oregon Coast is excerpted from:

Department of Land Conservation and Development. 2009. Climate Ready Communities: A Strategy for Adapting to Impacts of Climate Change on the Oregon Coast. Coast Oregon Coastal Management Program Salem, Oregon. Pp 11-12, 15-17, 20 [Accessed October 15, 2009].

Likely Effects of Climate Change on the Oregon Coast

The likely effects of climate change on the Oregon coast may come as no surprise to Oregonians who are familiar with winter storms and the variability of the climate and ocean conditions on the Oregon coast. The El Nio climate events of 1982-83 and 1997-98 gave Oregonians a taste of higher sea level, stronger storms, warmer ocean temperatures, and altered marine ecosystem.

Salmon River

Salmon River (Kenneth Popper,
The Nature Conservancy)

Oregon's coastal communities have begun to experience the effects climate change in the form of higher wave heights, more powerful winter storms, and major ocean shoreline erosion. Other phenomena are expected due to the Earths changing climate such as rising sea level and tidal height, hypoxic nearshore ocean waters, seasonal temperature changes, more acidic ocean waters, and changes in forest cover.

It is important that coastal communities understand the potential effects of climate change in order to take action to avoid risks, reduce damage and make choices that will maximize community resilience. This paper outlines some of the principal ways that the Oregon coast is likely to be affected.

Key Physical Changes in Oregon's Coastal Climate and Weather

Changes in Earths climate, driven by atmospheric warming caused by greenhouse gases, will affect the climate and weather of the Oregon coast in a variety of ways, some familiar, others dramatically new. Exactly how these changes will affect any particular community or region of the coast cannot now be accurately predicted. However, scientific evidence strongly suggests that coastal climate and weather are likely to change in four principal ways.

  • Temperature
    The current best estimate for future warming is about 0.5 degrees F per decade, at least in the next few decades. The Pacific Northwest is projected to have greater warming during summer than in the winter. The mean temperature may increase significantly beyond current ranges over the course of the next century
  • Storms
    Data show that both the frequency and intensity of storms have increased in recent years, and individual storms are producing higher waves and storm surges. Projected changes suggest that future winter storms may be similar to recent strong El Niño-influenced storms that accelerated coastal erosion. More frequent, longer and more intense storms will cause greater damage.
  • Sea level
    Sea level is expected to rise significantly by 2100 but how much cannot now be predicted for any given location. Average sea level rose worldwide about 6.7 inches in the 20th century. A recent report concluded that sea level could rise on the Washington coast by 22 inches by 2050 and by 50 inches by 2100. The most current projections do not include the effects of rapid ice melt being experienced in Greenland or Antarctica. Sea level rise will generate increased tidal heights in estuaries and coastal rivers that are affected by tides.
  • Precipitation
    Precipitation in the Pacific Northwest is expected to increase but to remain within historical ranges for rainfall. Winter precipitation is projected to increase, while summers will be longer and even drier than at present. For the Coast Range and lower elevations, precipitation will be mostly rain, as at present. Some research anticipates an increase in intense precipitation events.

Coastal Natural Systems

Many familiar coastal habitats, ecosystems, and natural resources will be affected by climate change. Low-lying habitats and ecosystems are especially vulnerable to floods, tides and ocean waves. Temperature and precipitation changes will affect the distribution and composition of forests, riparian areas, and other terrestrial habitats. Even rocky intertidal habitats are vulnerable to increased atmospheric and ocean temperatures.

  • Rivers and Streams
    • Coastal rivers: Streams that drain the Coast Range will carry increased runoff from greater winter rainfall but will become drier in summer due to decreased rainfall. More severe rainfall events in these streams may increase the frequency and severity of flooding episodes. Warmer summer temperatures and lower summer stream flows may raise water temperatures to the detriment of salmon and other cold-water species
    • Inland rivers: Snowmelt runoff is a factor in four rivers that are important to the Oregon coast and coastal fisheries: the Columbia, Umpqua, Rogue, and Klamath. For these rivers, less snow fall and more rain may alter seasonal flow regimes, resulting in lower stream flows in late spring through the summer and fall. Changes in flow regimes may affect salmonids that are adapted to these stream systems. For the Columbia River, the presence of dams and a highly-engineered hydrologic system complicate projections of impacts of climate change on the rivers natural resources and ecosystems.
  • Estuaries
    Estuaries are critical and unique habitats. Estuaries reflect a balance among competing natural forces. Sustained changes in sea level, tidal elevations, river flows, or sediment loads would necessarily alter the shape and productivity of Oregon estuaries.
    Estuarine wetlands are vulnerable to rising sea level and tidal elevations, depending on rate of sediment deposition, the nature of the shoreline, and pace of sea level rise. Freshwater tidal wetlands may be inundated more frequently by saline waters, triggering changes in wetland communities. Because most Oregon estuaries are sharply bounded by steep hillsides or dikes and levees, fringe wetlands will be unable to migrate landward and will be inundated due to increased tidal elevation. An adequate supply of sediments to the estuary could enable tidal wetland elevations to keep pace with rising tidal elevation.
    • Estuarine benthic ecosystems: Higher air temperatures can heat mudflats and raise estuarine water temperatures, especially upstream of ocean influence, thus affecting benthic communities and productivity. The loss of benthic habitat will directly affect the composition and productivity of estuarine ecosystems.
    • Ocean spits: Rising sea levels and increased storminess will likely result in the long-term movement of the sand spits that form the outer boundary of many Oregon estuaries. These forces could result in breaching of spits, as last occurred to the Tillamook spit in 1952, and which came close to occurring to the Netarts spit in 2007.
    • Invasive species: Estuaries in the Pacific Northwest have recently experienced biological invasions of non-native species that have had significant effects on estuarine communities. Such invasions may be related to climate factors.
    • Acidification: Oregon estuaries are dominated by ocean water due to high tidal flushing twice daily. As ocean waters become more acidic, estuaries will be subjected to these same acidic conditions. The effects of increased acidity on estuarine ecosystems are not yet known, but scientists are concerned about the potential effects on clams, crabs, oysters and other shellfish.
  • The Pacific Ocean
    • Ecosystem shifts: Summer winds are critical to upwelling that drives productivity of marine ecosystems. Recent El Nio events demonstrated that warmer ocean temperatures and shifting wind patterns can, from just one season to the next, affect upwelling and the production of phytoplankton, zooplankton, and forage fish. Seabirds, marine mammals, salmon and other species were adversely affected by El Nio conditions and are expected to be affected by long term shifts in climate conditions.
    • Distribution of species: Long-term changes in ocean conditions are likely to result in a northward shift in the distribution of marine species, including sea birds and marine mammals. El Nio conditions have been cited as a factor in marine mammal mortality, evidence of warm water fish in waters off Washington, and lack of seabird reproductive success.
    • Changes in upwelling: Timing of the seasonal upwelling in the Pacific off Oregon, which provides the nutritional foundation for the marine food web, is changing. A long-term shift in the timing of up-welling would have long-lasting effects on commercial and recreational fisheries in Oregon.
    • Hypoxia: While it is not clear that climate change is causing the hypoxic "dead zones" in ocean waters off Oregon, the forces causing the hypoxia are all linked to, and affected by, climate change.
    • Ocean acidification: Increasing ocean acidification due to its absorption of CO2 has the potential to reduce the ability of marine species to form shells, which in turn would have a dramatic effect on the entire marine food web. Shellfish such as clams, oysters, and crabs will be particularly sensitive to an increasingly acid environment.
  • Coastal shorelands
    • Ocean shore: The ocean shore will certainly be altered in many places due to higher sea level, higher waves, more frequent and stronger storms, and possible shifts in predominant wind directions. Beach and bluff erosion will result in shoreline retreat. Ocean shores armored with rip-rap and seawalls will be increasingly at risk over time.
    • Estuarine shores: The shorelines of estuaries will change over time as increasing tidal elevations push the "normal" shoreline farther inland. Habitats and human uses in low-lying areas adjacent to estuaries are at risk over time even if protected by bulkheads, dikes, or levees. Habitat restoration projects in coastal shorelands should consider effects of future climate change
  • Terrestrial and aquatic habitats
    • Habitat distribution and composition: Terrestrial and aquatic habitats, which reflect a balance of many factors, will be affected by changes in climate. As the suitability of habitats declines, the ranges of species will likewise shift. Salmon populations, especially, are vulnerable to increased water temperatures and other climate variables throughout their life histories.
    • Non-native species: Habitat changes in response to shifts in temperature, salinity, and precipitation will provide opportunities for invasion by non-native species that are adapted to the new habitat conditions or that out-compete native species weakened by habitat change....

Selected References

Fourth Assessment Report: Climate Change 2007. Intergovernmental Panel on Climate Change (IPCC), three volumes and synthesis report.

Potential Consequences of Climate Variability and Change for the Pacific Northwest. 2000. Chapter 9 of the US National Assessment of the Potential Consequences of Climate Variability and Change. 34 pp.

Scenarios of future climate for the Pacific Northwest. 2008. Climate Impacts Group, Center for Science in the Earth System, Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle.

Sea Level Rise in the Coastal Waters of Washington State. 2008. University of Washington Climate Impacts Group Seattle, WA.

Scientific Consensus Statement on the Likely Impacts of Climate Change on the Pacific Northwest. 2004. Appendix C to the Oregon Strategy for Greenhouse Gas Reductions. Compiled for 2004 symposium on "Impacts of Climate Change on the Pacific Northwest."

Final Report to the Governor: A Framework for Addressing Rapid Climate Change. 2008. The Governors Climate Change Integration Group. Oregon Department of Energy. Salem, OR.

The Potential Consequences of Climate Variability and Change on Coastal Areas and Marine Resources. 2000. Report of the Coastal Areas and Marine Resources Sector Team, U.S. National Assessment of the Potential Consequences of Climate Variability and Change, U.S. Global Change Research Program. NOAA Coastal Ocean Program Decision Analysis Series No. #21. NOAA Coastal Ocean Program, Silver Spring, MD.

A Survey of Climate Change Adaptation Planning. 2007. The H. John Heinz III Center for Science, Economics and the Environment, Washington, D.C.

Preparing for Climate Change: A Guidebook for Local, Regional, and State Governments. 2007. A comprehensive guide prepared and published by King County Washington and Climate Impacts Group at the University of Washington.

Compiled by Heather Stout, Oregon Wetlands Explorer Project (2009)


Department of Land Conservation and Development. 2009. Climate Ready Communities: A Strategy for Adapting to Impact of Climate Change on the Oregon. Coast Oregon Coastal Management Program Salem, Oregon. Pp 11-12, 15-17, 20 [Accessed October 15, 2009].

Lawler, J.J., M. Mathias, A.E. Yahnke, and E. H. Girvetz. 2008. Oregon's Biodiversity in a Changing Climate. 2008. Report prepared for the Climate Leadership Initiative, University of Oregon.