Get Set For Frequent Flooding In Coastal U.S. Cities

Sea level rise is increasing the odds of nuisance flooding

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A surfer rides large waves at Baker Beach in San Francisco during one of the largest storms to hit Northern California in the last five years. John Orvis/Demotix/Corbis

Over the past 170 years or so, the odds that storm water would crash over Manhattan's 5.74-foot-high Battery Park seawall lept 20-fold. In the mid-1800s the seawall would be overtopped roughly once every 100 to 400 years; between climate change and a re-engineered New York Harbor, Battery Park now faces inundation every four to five years.

New York is not the only coastal American city that faces a future of rampant flooding. And even within New York, not every part of the city is protected by a seawall. According to Climate Central, reporting on a new study, the damp future of climate change-enhanced flooding will be here for large parts of the country far sooner than scientists previously thought.

On the east, west and Gulf coasts, say scientists William Sweet and Joseph Park in their study, floods already seem to be growing more common. Based on tide gauge observations and forecasts of future climate change, the authors calculated that, in the next few decades, many U.S. cities will get hit by at least 30 days of flooding pear year on average.

The study focused on so-called “nuisance flooding,” where the water level is roughly 20 inches above high tide—rather than the more destructive levels of flooding cities might face during big storms. While these sorts of floods don't bring anywhere near the levels of devastation seen during Hurricanes Katrina or Sandy, for example, getting water in your basement 30 days a year is nothing to ignore, either.

“Impacts from recurrent coastal flooding include overwhelmed storm water drainage capacity at high tide, frequent road closures, and general deterioration and corrosion of infrastructure not designed to withstand frequent inundation or saltwater exposure,” say the authors in their study.

The 26 mainland U.S. cities looked at in the study (*list below) will all likely hit the 30 floods per year mark by 2050, or even sooner, says Climate Central:  

While most cities will reach that tipping point around 2050 unless greenhouse gas emissions are slowed, a number of locations will cross that line much sooner. Boston has nearly crossed that mark already and New York and Philadelphia are likely to reach the 30-day flood threshold at some point in the 2020s.

There's no question now that the threat of nuisance flooding will increase; instead, city leaders need to figure out what to do about it, says Climate Central.

Reaching those levels is a near guarantee due to the sea level rise already locked in. After that, the world’s choice on when or if to reduce greenhouse emissions will determine just how regular future flooding will be. In cities such as Norfolk and San Francisco, it will become a daily problem by the 2070s on the current emissions pathway, at which points seas could be up to 4 feet higher, according to recent climate projections.

*Boston, MA; Providence, RI; New London, CT; Montauk, NY; Kings Point, NY; New York City, NY; Sandy Hook, NJ; Atlantic City, NJ; Philadelphia, PA; Lewes, DE; Baltomore, MD; Annapolis, MD; Washington D.C.; Norfolk, VA; Wilmington, NC; Charleston, SC; Fort Paluski, GA; Fernandina Beach, FL; Mayport, FL; Key West, FL; St. Petersburg, FL; Galveston Bay, TX; Port Isabel, TX; La Jolla, CA; San Francisco, CA; and Seattle, WA