Cities lining the U.S. coasts should brace for a lot more flooding — from “nuisance” floods that shut down streets during high tides to deluges that take lives and wipe out infrastructure. In a new study published Wednesday, researchers from Princeton and Rutgers universities warn that the current flooding predictions, including those widely used by policy makers, don’t accurately reflect the frequency and types of floods that are likely to challenge American cities in the coming decades as global temperatures and sea levels rise.
Their research found that major coastal flooding—expected to occur only once every 100 years—will inundate coastal cities an average of 40 times more often by 2050, likely overwhelming the cities’ abilities to protect themselves.
After 2050, the picture looks worse. Major flooding could slosh through the streets of New York City every other month by the end of the century, while major floods could sweep into Seattle nearly every week…
Maya K Buchanan1,4, Michael Oppenheimer1,2 and Robert E Kopp3 Amplification of flood frequencies with local sea level rise and emerging flood regimes Published 7 June 2017 • © 2017 IOP Publishing Ltd , ,
Abstract The amplification of flood frequencies by sea level rise (SLR) is expected to become one of the most economically damaging impacts of climate change for many coastal locations. Understanding the magnitude and pattern by which the frequency of current flood levels increase is important for developing more resilient coastal settlements, particularly since flood risk management (e.g. infrastructure, insurance, communications) is often tied to estimates of flood return periods. The Intergovernmental Panel on Climate Change’s Fifth Assessment Report characterized the multiplication factor by which the frequency of flooding of a given height increases (referred to here as an amplification factor; AF). However, this characterization neither rigorously considered uncertainty in SLR nor distinguished between the amplification of different flooding levels (such as the 10% versus 0.2% annual chance floods); therefore, it may be seriously misleading. Because both historical flood frequency and projected SLR are uncertain, we combine joint probability distributions of the two to calculate AFs and their uncertainties over time. Under probabilistic relative sea level projections, while maintaining storm frequency fixed, we estimate a median 40-fold increase (ranging from 1- to 1314-fold) in the expected annual number of local 100-year floods for tide-gauge locations along the contiguous US coastline by 2050. While some places can expect disproportionate amplification of higher frequency events and thus primarily a greater number of historically precedented floods, others face amplification of lower frequency events and thus a particularly fast growing risk of historically unprecedented flooding. For example, with 50 cm of SLR, the 10%, 1%, and 0.2% annual chance floods are expected respectively to recur 108, 335, and 814 times as often in Seattle, but 148, 16, and 4 times as often in Charleston, SC.