Nuisance flooding, which causes such public inconveniences as frequent road closures, overwhelmed storm drains and compromised infrastructure, has increased on all three U.S. coasts between 300% and 925% since the 1960s due to rising sea levels, according to a National Oceanic and Atmospheric Administration report released in June.

The NOAA report, Sea Level Rise and Nuisance Flood Frequency Changes around the United States, also finds Annapolis, Md.. and Baltimore lead the list with an increase in number of flood days of more than 920% since 1960. Port Isabel, Texas, along the Gulf coast, showed an increase of 547% and nuisance flood days in San Francisco increased 364%.

The study was conducted by scientists at CO-OPS, who looked at data from 45 NOAA water level gauges with long data records around the country and compared that to reports of number of days of nuisance floods.

The report provides critical NOAA environmental data that can help coastal communities assess flooding risk, develop ways to mitigate and adapt to the effects of sea level rise and improve coastal resiliency in the face of climate- and weather-induced changes.

“As relative sea level increases, it no longer takes a strong storm or a hurricane to cause flooding,” said Dr. William Sweet, an oceanographer at NOAA’s Center for Operational Oceanographic Products and Services (CO-OPS) and the report’s lead author. “Flooding now occurs with high tides in many locations due to climate-related sea level rise, land subsidence and the loss of natural barriers.”  

The report concludes that any acceleration in sea level rise that is predicted to occur this century will further intensify nuisance flooding impacts over time, and will further reduce the time between flood events.