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<br /> <br />5.6.2 Probability of Future Flooding <br />Globally, sea levels are rising due to thermal expansion caused by the ocean warming and <br />the melting of land‐based ice such as glaciers and polar ice caps. Regionally and locally, the <br />rate of sea level rise is affected by other processes, including changes in land elevation <br />(subsidence or uplift), coastal erosion, wind and ocean currents, ocean temperature and <br />salinity, atmospheric pressure, and large‐scale climate regimes.24 <br /> <br />The National Research Council (NRC) Sea-Level Rise for the Coasts of California, Oregon, and <br />Washington study, released June 2012, provides regionally specific sea level rise <br />projections for the Coasts of California, Oregon, and Washington. Because there is <br />significant uncertainty in how much sea level will rise, the range in projected values <br />increases over time. <br /> <br />Table 4: Regional Sea Level Rise Projections Relative to Year 2000 for the California Coast <br />South of Cape Mendocino25 <br /> Sea Level Rise (inches) <br />Year <br />NRC 2012 Projection <br />(mean ± the standard deviation <br />for the A1B Scenario26) <br />Low <br />(mean of the B1 scenario) <br />High <br />(mean of the A1F1 <br />scenario) <br />2030 5.6 (±1.9) 2 12 <br />2050 11.0 (±3.6) 5 24 <br />2100 36.1 (±10) 17 66 <br /> <br /> <br />Sea level rise has the potential to influence the impact of coastal, riverine and localized <br />nuisance flooding. In particular, without intervention rising sea levels may cause: <br />More frequent floods: Rising sea levels can lead to more frequent flooding of existing <br />flood-prone areas, including more frequent overtopping and overbank flooding of riverine <br />systems that already flood when rainfall coincides with high tides due to the increased <br />backwater effect. In addition, gravity drained and pumped systems that discharge <br />stormwater into flood control channels can have reduced performance, causing backups <br />and flooding of streets and basements. <br /> <br />24 Committee on Sea Level Rise in California, Oregon, and Washington, and Board on Earth Sciences and <br />Resources and Ocean Studies Board, Division on Earth and Life Studies, (2012) <br />25 Committee on Sea Level Rise in California, Oregon, and Washington, and Board on Earth Sciences and <br />Resources and Ocean Studies Board, Division on Earth and Life Studies, (2012). <br />26 The A1 scenario family assumes high economic growth, low population growth that peaks mid-century, and the <br />rapid introduction of more efficient technologies (A1B is balanced and A1FI is fossil fuel intensive). The B1 <br />scenario family assumes the same low population growth as the A1 scenarios, but a shift toward a lower-emission <br />service and information economy and cleaner technologies.