An analysis of tidal levels and flood data by the news organization Reuters concludes that flooding has increased along the Eastern Seaboard over the past four decades.
During that period, the number of days a year that tidal waters reached or exceeded National Oceanic and Atmospheric Administration flood thresholds more than tripled in many places. The trend roughly tracks a global rise in sea levels, with an average rise of 8 inches in the past century, according to the 2014 National Climate Assessment.
At flood threshold, water begins pool on streets. If it rises beyond that point, it can close roads, damage property, and overwhelm drainage systems. Since 2001, water has reached flood levels an average of 20 days or more a year in Annapolis, Maryland; Wilmington, North Carolina; Washington, D.C.; Atlantic City, New Jersey; Sandy Hook, New Jersey; and Charleston, South Carolina. Before 1971, none of those locations averaged more than five days a year of flooding.
Reuters’s analysis was based on more than 25 million hourly tide-gauge readings from nearly 70 sites on the Atlantic, Gulf, and Pacific coasts and a comparison of that data to NOAA flood thresholds. Reuters then narrowed the analysis to 25 gauges with data spanning at least 50 years. The organization plans to publish a more in-depth examination of rising sea levels later this year.