Wave Climate Change and Coastal Erosion in the US Pacific Northwest

Wave-buoy data collected off the coast of the US Pacific Northwest (Washington and Oregon) document that significant wave heights and periods have progressively increased during recent decades. The average deep-water significant wave heights during the "winter" (October through March) have increased at a rate 0.032 m/yr from 1978 through 2001, a 0.77-m change, while the increase in wave heights associated with the strongest storms has been even greater. Calculated swash runup levels on beaches, which depend on both deep-water wave heights and periods, show parallel increases; the rate of increase has been 0.010 m/yr, which would have produced more than a 6-m landward shift in the mean shoreline during the winter since the late 1970's. Such decadal trends, together with extreme-value analyses of deep-water wave parameters and swash runup levels, are being used to assess the potential for future beach and property erosion along the Pacific Northwest coast.