The number of high-tide floods each year in some US towns may triple in the next 15 years and in 30 years a ten-fold increase compared to historic levels may be seen, scientists have warned.
Flooding during high tides is now common in some places in the US and is projected to grow to the point that sections of coastal cities may flood so often they would become unusable in the near future, scientists say.
The study by the Union of Concerned Scientists (UCS) is based on an analysis of 52 National Oceanic and Atmospheric Administration (NOAA) tide gauges in communities stretching from Portland, Maine to Freeport, Texas, using moderate sea level rise projections.
The analysis found that in the next 15 years, most of the towns analysed could see a tripling in the number of high-tide floods each year and in 30 years a ten-fold increase compared to historic levels.
The problem will rapidly worsen as sea level rises. In 15 years' time, most of the communities analysed are projected to experience at least 24 floods per year in exposed areas, the equivalent of flooding twice a month.
In 15 years' time, 15 of the communities can expect to see at least 48 floods a year, the equivalent of flooding four times a month. In 30 years' time, most of the towns analysed would see at least 48 floods a year, the equivalent of four floods a month.
In 30 years' time, half of the towns are expected to face more than 100 floods a year, the equivalent of eight floods a month, 17 towns would face at least 180 floods a year, or 15 floods each month and nine towns could see tidal flooding 240 times or more per year.
"This report shows that, within the timeframe of a 30-year mortgage, many East Coast communities will see dramatic changes in the number and severity of tidal floods each year, unless, of course, successful steps are taken to manage those floodwaters," said Erika Spanger-Siegfried, report co-author and senior analyst at UCS.
Meanwhile, with only a few exceptions, most floods that now occur at high tide are classified as "nuisance" or minor floods.
The UCS analysis found that in 15 years, the tides that cause today's nuisance floods will be capable of causing "extensive" floods in seven cities - floods that are deeper, reach further inland, last longer and threaten life and property.
Today, US cities typically only experience extensive floods during storms and when high winds push an extreme high tide further inland. In 30 years, nearly half the towns analysed would experience extensive floods with tides alone.
The study also found that along the East Coast of the US, Mid-Atlantic communities will see the greatest increase in the number of floods each year because, in addition to sea level rise, the land is sinking and ocean dynamics are changing.
The analysis projects that in 30 years' time, Annapolis, Lewisetta, Washington, DC and Wilmington would each see well over 300 flooding events per year.
